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dibbler/sqlalchemy/sql/selectable.py

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Updated SqlAlchemy + the new files
2017-04-15 18:33:29 +02:00
# sql/selectable.py
# Copyright (C) 2005-2017 the SQLAlchemy authors and contributors
# <see AUTHORS file>
#
# This module is part of SQLAlchemy and is released under
# the MIT License: http://www.opensource.org/licenses/mit-license.php
"""The :class:`.FromClause` class of SQL expression elements, representing
SQL tables and derived rowsets.
"""
from .elements import ClauseElement, TextClause, ClauseList, \
and_, Grouping, UnaryExpression, literal_column, BindParameter
from .elements import _clone, \
_literal_as_text, _interpret_as_column_or_from, _expand_cloned,\
_select_iterables, _anonymous_label, _clause_element_as_expr,\
_cloned_intersection, _cloned_difference, True_, \
_literal_as_label_reference, _literal_and_labels_as_label_reference
from .base import Immutable, Executable, _generative, \
ColumnCollection, ColumnSet, _from_objects, Generative
from . import type_api
from .. import inspection
from .. import util
from .. import exc
from operator import attrgetter
from . import operators
import operator
import collections
from .annotation import Annotated
import itertools
from sqlalchemy.sql.visitors import Visitable
def _interpret_as_from(element):
insp = inspection.inspect(element, raiseerr=False)
if insp is None:
if isinstance(element, util.string_types):
util.warn_limited(
"Textual SQL FROM expression %(expr)r should be "
"explicitly declared as text(%(expr)r), "
"or use table(%(expr)r) for more specificity",
{"expr": util.ellipses_string(element)})
return TextClause(util.text_type(element))
try:
return insp.selectable
except AttributeError:
raise exc.ArgumentError("FROM expression expected")
def _interpret_as_select(element):
element = _interpret_as_from(element)
if isinstance(element, Alias):
element = element.original
if not isinstance(element, SelectBase):
element = element.select()
return element
class _OffsetLimitParam(BindParameter):
@property
def _limit_offset_value(self):
return self.effective_value
def _offset_or_limit_clause(element, name=None, type_=None):
"""Convert the given value to an "offset or limit" clause.
This handles incoming integers and converts to an expression; if
an expression is already given, it is passed through.
"""
if element is None:
return None
elif hasattr(element, '__clause_element__'):
return element.__clause_element__()
elif isinstance(element, Visitable):
return element
else:
value = util.asint(element)
return _OffsetLimitParam(name, value, type_=type_, unique=True)
def _offset_or_limit_clause_asint(clause, attrname):
"""Convert the "offset or limit" clause of a select construct to an
integer.
This is only possible if the value is stored as a simple bound parameter.
Otherwise, a compilation error is raised.
"""
if clause is None:
return None
try:
value = clause._limit_offset_value
except AttributeError:
raise exc.CompileError(
"This SELECT structure does not use a simple "
"integer value for %s" % attrname)
else:
return util.asint(value)
def subquery(alias, *args, **kwargs):
r"""Return an :class:`.Alias` object derived
from a :class:`.Select`.
name
alias name
\*args, \**kwargs
all other arguments are delivered to the
:func:`select` function.
"""
return Select(*args, **kwargs).alias(alias)
def alias(selectable, name=None, flat=False):
"""Return an :class:`.Alias` object.
An :class:`.Alias` represents any :class:`.FromClause`
with an alternate name assigned within SQL, typically using the ``AS``
clause when generated, e.g. ``SELECT * FROM table AS aliasname``.
Similar functionality is available via the
:meth:`~.FromClause.alias` method
available on all :class:`.FromClause` subclasses.
When an :class:`.Alias` is created from a :class:`.Table` object,
this has the effect of the table being rendered
as ``tablename AS aliasname`` in a SELECT statement.
For :func:`.select` objects, the effect is that of creating a named
subquery, i.e. ``(select ...) AS aliasname``.
The ``name`` parameter is optional, and provides the name
to use in the rendered SQL. If blank, an "anonymous" name
will be deterministically generated at compile time.
Deterministic means the name is guaranteed to be unique against
other constructs used in the same statement, and will also be the
same name for each successive compilation of the same statement
object.
:param selectable: any :class:`.FromClause` subclass,
such as a table, select statement, etc.
:param name: string name to be assigned as the alias.
If ``None``, a name will be deterministically generated
at compile time.
:param flat: Will be passed through to if the given selectable
is an instance of :class:`.Join` - see :meth:`.Join.alias`
for details.
.. versionadded:: 0.9.0
"""
return _interpret_as_from(selectable).alias(name=name, flat=flat)
def lateral(selectable, name=None):
"""Return a :class:`.Lateral` object.
:class:`.Lateral` is an :class:`.Alias` subclass that represents
a subquery with the LATERAL keyword applied to it.
The special behavior of a LATERAL subquery is that it appears in the
FROM clause of an enclosing SELECT, but may correlate to other
FROM clauses of that SELECT. It is a special case of subquery
only supported by a small number of backends, currently more recent
PostgreSQL versions.
.. versionadded:: 1.1
.. seealso::
:ref:`lateral_selects` - overview of usage.
"""
return _interpret_as_from(selectable).lateral(name=name)
def tablesample(selectable, sampling, name=None, seed=None):
"""Return a :class:`.TableSample` object.
:class:`.TableSample` is an :class:`.Alias` subclass that represents
a table with the TABLESAMPLE clause applied to it.
:func:`~.expression.tablesample`
is also available from the :class:`.FromClause` class via the
:meth:`.FromClause.tablesample` method.
The TABLESAMPLE clause allows selecting a randomly selected approximate
percentage of rows from a table. It supports multiple sampling methods,
most commonly BERNOULLI and SYSTEM.
e.g.::
from sqlalchemy import func
selectable = people.tablesample(
func.bernoulli(1),
name='alias',
seed=func.random())
stmt = select([selectable.c.people_id])
Assuming ``people`` with a column ``people_id``, the above
statement would render as::
SELECT alias.people_id FROM
people AS alias TABLESAMPLE bernoulli(:bernoulli_1)
REPEATABLE (random())
.. versionadded:: 1.1
:param sampling: a ``float`` percentage between 0 and 100 or
:class:`.functions.Function`.
:param name: optional alias name
:param seed: any real-valued SQL expression. When specified, the
REPEATABLE sub-clause is also rendered.
"""
return _interpret_as_from(selectable).tablesample(
sampling, name=name, seed=seed)
class Selectable(ClauseElement):
"""mark a class as being selectable"""
__visit_name__ = 'selectable'
is_selectable = True
@property
def selectable(self):
return self
class HasPrefixes(object):
_prefixes = ()
@_generative
def prefix_with(self, *expr, **kw):
r"""Add one or more expressions following the statement keyword, i.e.
SELECT, INSERT, UPDATE, or DELETE. Generative.
This is used to support backend-specific prefix keywords such as those
provided by MySQL.
E.g.::
stmt = table.insert().prefix_with("LOW_PRIORITY", dialect="mysql")
Multiple prefixes can be specified by multiple calls
to :meth:`.prefix_with`.
:param \*expr: textual or :class:`.ClauseElement` construct which
will be rendered following the INSERT, UPDATE, or DELETE
keyword.
:param \**kw: A single keyword 'dialect' is accepted. This is an
optional string dialect name which will
limit rendering of this prefix to only that dialect.
"""
dialect = kw.pop('dialect', None)
if kw:
raise exc.ArgumentError("Unsupported argument(s): %s" %
",".join(kw))
self._setup_prefixes(expr, dialect)
def _setup_prefixes(self, prefixes, dialect=None):
self._prefixes = self._prefixes + tuple(
[(_literal_as_text(p, warn=False), dialect) for p in prefixes])
class HasSuffixes(object):
_suffixes = ()
@_generative
def suffix_with(self, *expr, **kw):
r"""Add one or more expressions following the statement as a whole.
This is used to support backend-specific suffix keywords on
certain constructs.
E.g.::
stmt = select([col1, col2]).cte().suffix_with(
"cycle empno set y_cycle to 1 default 0", dialect="oracle")
Multiple suffixes can be specified by multiple calls
to :meth:`.suffix_with`.
:param \*expr: textual or :class:`.ClauseElement` construct which
will be rendered following the target clause.
:param \**kw: A single keyword 'dialect' is accepted. This is an
optional string dialect name which will
limit rendering of this suffix to only that dialect.
"""
dialect = kw.pop('dialect', None)
if kw:
raise exc.ArgumentError("Unsupported argument(s): %s" %
",".join(kw))
self._setup_suffixes(expr, dialect)
def _setup_suffixes(self, suffixes, dialect=None):
self._suffixes = self._suffixes + tuple(
[(_literal_as_text(p, warn=False), dialect) for p in suffixes])
class FromClause(Selectable):
"""Represent an element that can be used within the ``FROM``
clause of a ``SELECT`` statement.
The most common forms of :class:`.FromClause` are the
:class:`.Table` and the :func:`.select` constructs. Key
features common to all :class:`.FromClause` objects include:
* a :attr:`.c` collection, which provides per-name access to a collection
of :class:`.ColumnElement` objects.
* a :attr:`.primary_key` attribute, which is a collection of all those
:class:`.ColumnElement` objects that indicate the ``primary_key`` flag.
* Methods to generate various derivations of a "from" clause, including
:meth:`.FromClause.alias`, :meth:`.FromClause.join`,
:meth:`.FromClause.select`.
"""
__visit_name__ = 'fromclause'
named_with_column = False
_hide_froms = []
_is_join = False
_is_select = False
_is_from_container = False
_textual = False
"""a marker that allows us to easily distinguish a :class:`.TextAsFrom`
or similar object from other kinds of :class:`.FromClause` objects."""
schema = None
"""Define the 'schema' attribute for this :class:`.FromClause`.
This is typically ``None`` for most objects except that of
:class:`.Table`, where it is taken as the value of the
:paramref:`.Table.schema` argument.
"""
def _translate_schema(self, effective_schema, map_):
return effective_schema
_memoized_property = util.group_expirable_memoized_property(["_columns"])
@util.deprecated(
'1.1',
message="``FromClause.count()`` is deprecated. Counting "
"rows requires that the correct column expression and "
"accommodations for joins, DISTINCT, etc. must be made, "
"otherwise results may not be what's expected. "
"Please use an appropriate ``func.count()`` expression "
"directly.")
@util.dependencies("sqlalchemy.sql.functions")
def count(self, functions, whereclause=None, **params):
"""return a SELECT COUNT generated against this
:class:`.FromClause`.
The function generates COUNT against the
first column in the primary key of the table, or against
the first column in the table overall. Explicit use of
``func.count()`` should be preferred::
row_count = conn.scalar(
select([func.count('*')]).select_from(table)
)
.. seealso::
:data:`.func`
"""
if self.primary_key:
col = list(self.primary_key)[0]
else:
col = list(self.columns)[0]
return Select(
[functions.func.count(col).label('tbl_row_count')],
whereclause,
from_obj=[self],
**params)
def select(self, whereclause=None, **params):
"""return a SELECT of this :class:`.FromClause`.
.. seealso::
:func:`~.sql.expression.select` - general purpose
method which allows for arbitrary column lists.
"""
return Select([self], whereclause, **params)
def join(self, right, onclause=None, isouter=False, full=False):
"""Return a :class:`.Join` from this :class:`.FromClause`
to another :class:`FromClause`.
E.g.::
from sqlalchemy import join
j = user_table.join(address_table,
user_table.c.id == address_table.c.user_id)
stmt = select([user_table]).select_from(j)
would emit SQL along the lines of::
SELECT user.id, user.name FROM user
JOIN address ON user.id = address.user_id
:param right: the right side of the join; this is any
:class:`.FromClause` object such as a :class:`.Table` object, and
may also be a selectable-compatible object such as an ORM-mapped
class.
:param onclause: a SQL expression representing the ON clause of the
join. If left at ``None``, :meth:`.FromClause.join` will attempt to
join the two tables based on a foreign key relationship.
:param isouter: if True, render a LEFT OUTER JOIN, instead of JOIN.
:param full: if True, render a FULL OUTER JOIN, instead of LEFT OUTER
JOIN. Implies :paramref:`.FromClause.join.isouter`.
.. versionadded:: 1.1
.. seealso::
:func:`.join` - standalone function
:class:`.Join` - the type of object produced
"""
return Join(self, right, onclause, isouter, full)
def outerjoin(self, right, onclause=None, full=False):
"""Return a :class:`.Join` from this :class:`.FromClause`
to another :class:`FromClause`, with the "isouter" flag set to
True.
E.g.::
from sqlalchemy import outerjoin
j = user_table.outerjoin(address_table,
user_table.c.id == address_table.c.user_id)
The above is equivalent to::
j = user_table.join(
address_table,
user_table.c.id == address_table.c.user_id,
isouter=True)
:param right: the right side of the join; this is any
:class:`.FromClause` object such as a :class:`.Table` object, and
may also be a selectable-compatible object such as an ORM-mapped
class.
:param onclause: a SQL expression representing the ON clause of the
join. If left at ``None``, :meth:`.FromClause.join` will attempt to
join the two tables based on a foreign key relationship.
:param full: if True, render a FULL OUTER JOIN, instead of
LEFT OUTER JOIN.
.. versionadded:: 1.1
.. seealso::
:meth:`.FromClause.join`
:class:`.Join`
"""
return Join(self, right, onclause, True, full)
def alias(self, name=None, flat=False):
"""return an alias of this :class:`.FromClause`.
This is shorthand for calling::
from sqlalchemy import alias
a = alias(self, name=name)
See :func:`~.expression.alias` for details.
"""
return Alias(self, name)
def lateral(self, name=None):
"""Return a LATERAL alias of this :class:`.FromClause`.
The return value is the :class:`.Lateral` construct also
provided by the top-level :func:`~.expression.lateral` function.
.. versionadded:: 1.1
.. seealso::
:ref:`lateral_selects` - overview of usage.
"""
return Lateral(self, name)
def tablesample(self, sampling, name=None, seed=None):
"""Return a TABLESAMPLE alias of this :class:`.FromClause`.
The return value is the :class:`.TableSample` construct also
provided by the top-level :func:`~.expression.tablesample` function.
.. versionadded:: 1.1
.. seealso::
:func:`~.expression.tablesample` - usage guidelines and parameters
"""
return TableSample(self, sampling, name, seed)
def is_derived_from(self, fromclause):
"""Return True if this FromClause is 'derived' from the given
FromClause.
An example would be an Alias of a Table is derived from that Table.
"""
# this is essentially an "identity" check in the base class.
# Other constructs override this to traverse through
# contained elements.
return fromclause in self._cloned_set
def _is_lexical_equivalent(self, other):
"""Return True if this FromClause and the other represent
the same lexical identity.
This tests if either one is a copy of the other, or
if they are the same via annotation identity.
"""
return self._cloned_set.intersection(other._cloned_set)
@util.dependencies("sqlalchemy.sql.util")
def replace_selectable(self, sqlutil, old, alias):
"""replace all occurrences of FromClause 'old' with the given Alias
object, returning a copy of this :class:`.FromClause`.
"""
return sqlutil.ClauseAdapter(alias).traverse(self)
def correspond_on_equivalents(self, column, equivalents):
"""Return corresponding_column for the given column, or if None
search for a match in the given dictionary.
"""
col = self.corresponding_column(column, require_embedded=True)
if col is None and col in equivalents:
for equiv in equivalents[col]:
nc = self.corresponding_column(equiv, require_embedded=True)
if nc:
return nc
return col
def corresponding_column(self, column, require_embedded=False):
"""Given a :class:`.ColumnElement`, return the exported
:class:`.ColumnElement` object from this :class:`.Selectable`
which corresponds to that original
:class:`~sqlalchemy.schema.Column` via a common ancestor
column.
:param column: the target :class:`.ColumnElement` to be matched
:param require_embedded: only return corresponding columns for
the given :class:`.ColumnElement`, if the given
:class:`.ColumnElement` is actually present within a sub-element
of this :class:`.FromClause`. Normally the column will match if
it merely shares a common ancestor with one of the exported
columns of this :class:`.FromClause`.
"""
def embedded(expanded_proxy_set, target_set):
for t in target_set.difference(expanded_proxy_set):
if not set(_expand_cloned([t])
).intersection(expanded_proxy_set):
return False
return True
# don't dig around if the column is locally present
if self.c.contains_column(column):
return column
col, intersect = None, None
target_set = column.proxy_set
cols = self.c._all_columns
for c in cols:
expanded_proxy_set = set(_expand_cloned(c.proxy_set))
i = target_set.intersection(expanded_proxy_set)
if i and (not require_embedded
or embedded(expanded_proxy_set, target_set)):
if col is None:
# no corresponding column yet, pick this one.
col, intersect = c, i
elif len(i) > len(intersect):
# 'c' has a larger field of correspondence than
# 'col'. i.e. selectable.c.a1_x->a1.c.x->table.c.x
# matches a1.c.x->table.c.x better than
# selectable.c.x->table.c.x does.
col, intersect = c, i
elif i == intersect:
# they have the same field of correspondence. see
# which proxy_set has fewer columns in it, which
# indicates a closer relationship with the root
# column. Also take into account the "weight"
# attribute which CompoundSelect() uses to give
# higher precedence to columns based on vertical
# position in the compound statement, and discard
# columns that have no reference to the target
# column (also occurs with CompoundSelect)
col_distance = util.reduce(
operator.add,
[sc._annotations.get('weight', 1) for sc in
col.proxy_set if sc.shares_lineage(column)])
c_distance = util.reduce(
operator.add,
[sc._annotations.get('weight', 1) for sc in
c.proxy_set if sc.shares_lineage(column)])
if c_distance < col_distance:
col, intersect = c, i
return col
@property
def description(self):
"""a brief description of this FromClause.
Used primarily for error message formatting.
"""
return getattr(self, 'name', self.__class__.__name__ + " object")
def _reset_exported(self):
"""delete memoized collections when a FromClause is cloned."""
self._memoized_property.expire_instance(self)
@_memoized_property
def columns(self):
"""A named-based collection of :class:`.ColumnElement` objects
maintained by this :class:`.FromClause`.
The :attr:`.columns`, or :attr:`.c` collection, is the gateway
to the construction of SQL expressions using table-bound or
other selectable-bound columns::
select([mytable]).where(mytable.c.somecolumn == 5)
"""
if '_columns' not in self.__dict__:
self._init_collections()
self._populate_column_collection()
return self._columns.as_immutable()
@_memoized_property
def primary_key(self):
"""Return the collection of Column objects which comprise the
primary key of this FromClause."""
self._init_collections()
self._populate_column_collection()
return self.primary_key
@_memoized_property
def foreign_keys(self):
"""Return the collection of ForeignKey objects which this
FromClause references."""
self._init_collections()
self._populate_column_collection()
return self.foreign_keys
c = property(attrgetter('columns'),
doc="An alias for the :attr:`.columns` attribute.")
_select_iterable = property(attrgetter('columns'))
def _init_collections(self):
assert '_columns' not in self.__dict__
assert 'primary_key' not in self.__dict__
assert 'foreign_keys' not in self.__dict__
self._columns = ColumnCollection()
self.primary_key = ColumnSet()
self.foreign_keys = set()
@property
def _cols_populated(self):
return '_columns' in self.__dict__
def _populate_column_collection(self):
"""Called on subclasses to establish the .c collection.
Each implementation has a different way of establishing
this collection.
"""
def _refresh_for_new_column(self, column):
"""Given a column added to the .c collection of an underlying
selectable, produce the local version of that column, assuming this
selectable ultimately should proxy this column.
this is used to "ping" a derived selectable to add a new column
to its .c. collection when a Column has been added to one of the
Table objects it ultimtely derives from.
If the given selectable hasn't populated its .c. collection yet,
it should at least pass on the message to the contained selectables,
but it will return None.
This method is currently used by Declarative to allow Table
columns to be added to a partially constructed inheritance
mapping that may have already produced joins. The method
isn't public right now, as the full span of implications
and/or caveats aren't yet clear.
It's also possible that this functionality could be invoked by
default via an event, which would require that
selectables maintain a weak referencing collection of all
derivations.
"""
if not self._cols_populated:
return None
elif (column.key in self.columns and
self.columns[column.key] is column):
return column
else:
return None
class Join(FromClause):
"""represent a ``JOIN`` construct between two :class:`.FromClause`
elements.
The public constructor function for :class:`.Join` is the module-level
:func:`.join()` function, as well as the :meth:`.FromClause.join` method
of any :class:`.FromClause` (e.g. such as :class:`.Table`).
.. seealso::
:func:`.join`
:meth:`.FromClause.join`
"""
__visit_name__ = 'join'
_is_join = True
def __init__(self, left, right, onclause=None, isouter=False, full=False):
"""Construct a new :class:`.Join`.
The usual entrypoint here is the :func:`~.expression.join`
function or the :meth:`.FromClause.join` method of any
:class:`.FromClause` object.
"""
self.left = _interpret_as_from(left)
self.right = _interpret_as_from(right).self_group()
if onclause is None:
self.onclause = self._match_primaries(self.left, self.right)
else:
self.onclause = onclause
self.isouter = isouter
self.full = full
@classmethod
def _create_outerjoin(cls, left, right, onclause=None, full=False):
"""Return an ``OUTER JOIN`` clause element.
The returned object is an instance of :class:`.Join`.
Similar functionality is also available via the
:meth:`~.FromClause.outerjoin()` method on any
:class:`.FromClause`.
:param left: The left side of the join.
:param right: The right side of the join.
:param onclause: Optional criterion for the ``ON`` clause, is
derived from foreign key relationships established between
left and right otherwise.
To chain joins together, use the :meth:`.FromClause.join` or
:meth:`.FromClause.outerjoin` methods on the resulting
:class:`.Join` object.
"""
return cls(left, right, onclause, isouter=True, full=full)
@classmethod
def _create_join(cls, left, right, onclause=None, isouter=False,
full=False):
"""Produce a :class:`.Join` object, given two :class:`.FromClause`
expressions.
E.g.::
j = join(user_table, address_table,
user_table.c.id == address_table.c.user_id)
stmt = select([user_table]).select_from(j)
would emit SQL along the lines of::
SELECT user.id, user.name FROM user
JOIN address ON user.id = address.user_id
Similar functionality is available given any
:class:`.FromClause` object (e.g. such as a :class:`.Table`) using
the :meth:`.FromClause.join` method.
:param left: The left side of the join.
:param right: the right side of the join; this is any
:class:`.FromClause` object such as a :class:`.Table` object, and
may also be a selectable-compatible object such as an ORM-mapped
class.
:param onclause: a SQL expression representing the ON clause of the
join. If left at ``None``, :meth:`.FromClause.join` will attempt to
join the two tables based on a foreign key relationship.
:param isouter: if True, render a LEFT OUTER JOIN, instead of JOIN.
:param full: if True, render a FULL OUTER JOIN, instead of JOIN.
.. versionadded:: 1.1
.. seealso::
:meth:`.FromClause.join` - method form, based on a given left side
:class:`.Join` - the type of object produced
"""
return cls(left, right, onclause, isouter, full)
@property
def description(self):
return "Join object on %s(%d) and %s(%d)" % (
self.left.description,
id(self.left),
self.right.description,
id(self.right))
def is_derived_from(self, fromclause):
return fromclause is self or \
self.left.is_derived_from(fromclause) or \
self.right.is_derived_from(fromclause)
def self_group(self, against=None):
return FromGrouping(self)
@util.dependencies("sqlalchemy.sql.util")
def _populate_column_collection(self, sqlutil):
columns = [c for c in self.left.columns] + \
[c for c in self.right.columns]
self.primary_key.extend(sqlutil.reduce_columns(
(c for c in columns if c.primary_key), self.onclause))
self._columns.update((col._label, col) for col in columns)
self.foreign_keys.update(itertools.chain(
*[col.foreign_keys for col in columns]))
def _refresh_for_new_column(self, column):
col = self.left._refresh_for_new_column(column)
if col is None:
col = self.right._refresh_for_new_column(column)
if col is not None:
if self._cols_populated:
self._columns[col._label] = col
self.foreign_keys.update(col.foreign_keys)
if col.primary_key:
self.primary_key.add(col)
return col
return None
def _copy_internals(self, clone=_clone, **kw):
self._reset_exported()
self.left = clone(self.left, **kw)
self.right = clone(self.right, **kw)
self.onclause = clone(self.onclause, **kw)
def get_children(self, **kwargs):
return self.left, self.right, self.onclause
def _match_primaries(self, left, right):
if isinstance(left, Join):
left_right = left.right
else:
left_right = None
return self._join_condition(left, right, a_subset=left_right)
@classmethod
def _join_condition(cls, a, b, ignore_nonexistent_tables=False,
a_subset=None,
consider_as_foreign_keys=None):
"""create a join condition between two tables or selectables.
e.g.::
join_condition(tablea, tableb)
would produce an expression along the lines of::
tablea.c.id==tableb.c.tablea_id
The join is determined based on the foreign key relationships
between the two selectables. If there are multiple ways
to join, or no way to join, an error is raised.
:param ignore_nonexistent_tables: Deprecated - this
flag is no longer used. Only resolution errors regarding
the two given tables are propagated.
:param a_subset: An optional expression that is a sub-component
of ``a``. An attempt will be made to join to just this sub-component
first before looking at the full ``a`` construct, and if found
will be successful even if there are other ways to join to ``a``.
This allows the "right side" of a join to be passed thereby
providing a "natural join".
"""
constraints = cls._joincond_scan_left_right(
a, a_subset, b, consider_as_foreign_keys)
if len(constraints) > 1:
cls._joincond_trim_constraints(
a, b, constraints, consider_as_foreign_keys)
if len(constraints) == 0:
if isinstance(b, FromGrouping):
hint = " Perhaps you meant to convert the right side to a "\
"subquery using alias()?"
else:
hint = ""
raise exc.NoForeignKeysError(
"Can't find any foreign key relationships "
"between '%s' and '%s'.%s" %
(a.description, b.description, hint))
crit = [(x == y) for x, y in list(constraints.values())[0]]
if len(crit) == 1:
return (crit[0])
else:
return and_(*crit)
@classmethod
def _joincond_scan_left_right(
cls, a, a_subset, b, consider_as_foreign_keys):
constraints = collections.defaultdict(list)
for left in (a_subset, a):
if left is None:
continue
for fk in sorted(
b.foreign_keys,
key=lambda fk: fk.parent._creation_order):
if consider_as_foreign_keys is not None and \
fk.parent not in consider_as_foreign_keys:
continue
try:
col = fk.get_referent(left)
except exc.NoReferenceError as nrte:
if nrte.table_name == left.name:
raise
else:
continue
if col is not None:
constraints[fk.constraint].append((col, fk.parent))
if left is not b:
for fk in sorted(
left.foreign_keys,
key=lambda fk: fk.parent._creation_order):
if consider_as_foreign_keys is not None and \
fk.parent not in consider_as_foreign_keys:
continue
try:
col = fk.get_referent(b)
except exc.NoReferenceError as nrte:
if nrte.table_name == b.name:
raise
else:
continue
if col is not None:
constraints[fk.constraint].append((col, fk.parent))
if constraints:
break
return constraints
@classmethod
def _joincond_trim_constraints(
cls, a, b, constraints, consider_as_foreign_keys):
# more than one constraint matched. narrow down the list
# to include just those FKCs that match exactly to
# "consider_as_foreign_keys".
if consider_as_foreign_keys:
for const in list(constraints):
if set(f.parent for f in const.elements) != set(
consider_as_foreign_keys):
del constraints[const]
# if still multiple constraints, but
# they all refer to the exact same end result, use it.
if len(constraints) > 1:
dedupe = set(tuple(crit) for crit in constraints.values())
if len(dedupe) == 1:
key = list(constraints)[0]
constraints = {key: constraints[key]}
if len(constraints) != 1:
raise exc.AmbiguousForeignKeysError(
"Can't determine join between '%s' and '%s'; "
"tables have more than one foreign key "
"constraint relationship between them. "
"Please specify the 'onclause' of this "
"join explicitly." % (a.description, b.description))
def select(self, whereclause=None, **kwargs):
r"""Create a :class:`.Select` from this :class:`.Join`.
The equivalent long-hand form, given a :class:`.Join` object
``j``, is::
from sqlalchemy import select
j = select([j.left, j.right], **kw).\
where(whereclause).\
select_from(j)
:param whereclause: the WHERE criterion that will be sent to
the :func:`select()` function
:param \**kwargs: all other kwargs are sent to the
underlying :func:`select()` function.
"""
collist = [self.left, self.right]
return Select(collist, whereclause, from_obj=[self], **kwargs)
@property
def bind(self):
return self.left.bind or self.right.bind
@util.dependencies("sqlalchemy.sql.util")
def alias(self, sqlutil, name=None, flat=False):
r"""return an alias of this :class:`.Join`.
The default behavior here is to first produce a SELECT
construct from this :class:`.Join`, then to produce an
:class:`.Alias` from that. So given a join of the form::
j = table_a.join(table_b, table_a.c.id == table_b.c.a_id)
The JOIN by itself would look like::
table_a JOIN table_b ON table_a.id = table_b.a_id
Whereas the alias of the above, ``j.alias()``, would in a
SELECT context look like::
(SELECT table_a.id AS table_a_id, table_b.id AS table_b_id,
table_b.a_id AS table_b_a_id
FROM table_a
JOIN table_b ON table_a.id = table_b.a_id) AS anon_1
The equivalent long-hand form, given a :class:`.Join` object
``j``, is::
from sqlalchemy import select, alias
j = alias(
select([j.left, j.right]).\
select_from(j).\
with_labels(True).\
correlate(False),
name=name
)
The selectable produced by :meth:`.Join.alias` features the same
columns as that of the two individual selectables presented under
a single name - the individual columns are "auto-labeled", meaning
the ``.c.`` collection of the resulting :class:`.Alias` represents
the names of the individual columns using a
``<tablename>_<columname>`` scheme::
j.c.table_a_id
j.c.table_b_a_id
:meth:`.Join.alias` also features an alternate
option for aliasing joins which produces no enclosing SELECT and
does not normally apply labels to the column names. The
``flat=True`` option will call :meth:`.FromClause.alias`
against the left and right sides individually.
Using this option, no new ``SELECT`` is produced;
we instead, from a construct as below::
j = table_a.join(table_b, table_a.c.id == table_b.c.a_id)
j = j.alias(flat=True)
we get a result like this::
table_a AS table_a_1 JOIN table_b AS table_b_1 ON
table_a_1.id = table_b_1.a_id
The ``flat=True`` argument is also propagated to the contained
selectables, so that a composite join such as::
j = table_a.join(
table_b.join(table_c,
table_b.c.id == table_c.c.b_id),
table_b.c.a_id == table_a.c.id
).alias(flat=True)
Will produce an expression like::
table_a AS table_a_1 JOIN (
table_b AS table_b_1 JOIN table_c AS table_c_1
ON table_b_1.id = table_c_1.b_id
) ON table_a_1.id = table_b_1.a_id
The standalone :func:`~.expression.alias` function as well as the
base :meth:`.FromClause.alias` method also support the ``flat=True``
argument as a no-op, so that the argument can be passed to the
``alias()`` method of any selectable.
.. versionadded:: 0.9.0 Added the ``flat=True`` option to create
"aliases" of joins without enclosing inside of a SELECT
subquery.
:param name: name given to the alias.
:param flat: if True, produce an alias of the left and right
sides of this :class:`.Join` and return the join of those
two selectables. This produces join expression that does not
include an enclosing SELECT.
.. versionadded:: 0.9.0
.. seealso::
:func:`~.expression.alias`
"""
if flat:
assert name is None, "Can't send name argument with flat"
left_a, right_a = self.left.alias(flat=True), \
self.right.alias(flat=True)
adapter = sqlutil.ClauseAdapter(left_a).\
chain(sqlutil.ClauseAdapter(right_a))
return left_a.join(right_a, adapter.traverse(self.onclause),
isouter=self.isouter, full=self.full)
else:
return self.select(use_labels=True, correlate=False).alias(name)
@property
def _hide_froms(self):
return itertools.chain(*[_from_objects(x.left, x.right)
for x in self._cloned_set])
@property
def _from_objects(self):
return [self] + \
self.onclause._from_objects + \
self.left._from_objects + \
self.right._from_objects
class Alias(FromClause):
"""Represents an table or selectable alias (AS).
Represents an alias, as typically applied to any table or
sub-select within a SQL statement using the ``AS`` keyword (or
without the keyword on certain databases such as Oracle).
This object is constructed from the :func:`~.expression.alias` module
level function as well as the :meth:`.FromClause.alias` method available
on all :class:`.FromClause` subclasses.
"""
__visit_name__ = 'alias'
named_with_column = True
_is_from_container = True
def __init__(self, selectable, name=None):
baseselectable = selectable
while isinstance(baseselectable, Alias):
baseselectable = baseselectable.element
self.original = baseselectable
self.supports_execution = baseselectable.supports_execution
if self.supports_execution:
self._execution_options = baseselectable._execution_options
self.element = selectable
if name is None:
if self.original.named_with_column:
name = getattr(self.original, 'name', None)
name = _anonymous_label('%%(%d %s)s' % (id(self), name
or 'anon'))
self.name = name
def self_group(self, target=None):
if isinstance(target, CompoundSelect) and \
isinstance(self.original, Select) and \
self.original._needs_parens_for_grouping():
return FromGrouping(self)
return super(Alias, self).self_group(target)
@property
def description(self):
if util.py3k:
return self.name
else:
return self.name.encode('ascii', 'backslashreplace')
def as_scalar(self):
try:
return self.element.as_scalar()
except AttributeError:
raise AttributeError("Element %s does not support "
"'as_scalar()'" % self.element)
def is_derived_from(self, fromclause):
if fromclause in self._cloned_set:
return True
return self.element.is_derived_from(fromclause)
def _populate_column_collection(self):
for col in self.element.columns._all_columns:
col._make_proxy(self)
def _refresh_for_new_column(self, column):
col = self.element._refresh_for_new_column(column)
if col is not None:
if not self._cols_populated:
return None
else:
return col._make_proxy(self)
else:
return None
def _copy_internals(self, clone=_clone, **kw):
# don't apply anything to an aliased Table
# for now. May want to drive this from
# the given **kw.
if isinstance(self.element, TableClause):
return
self._reset_exported()
self.element = clone(self.element, **kw)
baseselectable = self.element
while isinstance(baseselectable, Alias):
baseselectable = baseselectable.element
self.original = baseselectable
def get_children(self, column_collections=True, **kw):
if column_collections:
for c in self.c:
yield c
yield self.element
@property
def _from_objects(self):
return [self]
@property
def bind(self):
return self.element.bind
class Lateral(Alias):
"""Represent a LATERAL subquery.
This object is constructed from the :func:`~.expression.lateral` module
level function as well as the :meth:`.FromClause.lateral` method available
on all :class:`.FromClause` subclasses.
While LATERAL is part of the SQL standard, curently only more recent
PostgreSQL versions provide support for this keyword.
.. versionadded:: 1.1
.. seealso::
:ref:`lateral_selects` - overview of usage.
"""
__visit_name__ = 'lateral'
class TableSample(Alias):
"""Represent a TABLESAMPLE clause.
This object is constructed from the :func:`~.expression.tablesample` module
level function as well as the :meth:`.FromClause.tablesample` method available
on all :class:`.FromClause` subclasses.
.. versionadded:: 1.1
.. seealso::
:func:`~.expression.tablesample`
"""
__visit_name__ = 'tablesample'
def __init__(self, selectable, sampling,
name=None,
seed=None):
self.sampling = sampling
self.seed = seed
super(TableSample, self).__init__(selectable, name=name)
@util.dependencies("sqlalchemy.sql.functions")
def _get_method(self, functions):
if isinstance(self.sampling, functions.Function):
return self.sampling
else:
return functions.func.system(self.sampling)
class CTE(Generative, HasSuffixes, Alias):
"""Represent a Common Table Expression.
The :class:`.CTE` object is obtained using the
:meth:`.SelectBase.cte` method from any selectable.
See that method for complete examples.
.. versionadded:: 0.7.6
"""
__visit_name__ = 'cte'
def __init__(self, selectable,
name=None,
recursive=False,
_cte_alias=None,
_restates=frozenset(),
_suffixes=None):
self.recursive = recursive
self._cte_alias = _cte_alias
self._restates = _restates
if _suffixes:
self._suffixes = _suffixes
super(CTE, self).__init__(selectable, name=name)
def _copy_internals(self, clone=_clone, **kw):
super(CTE, self)._copy_internals(clone, **kw)
if self._cte_alias is not None:
self._cte_alias = self
self._restates = frozenset([
clone(elem, **kw) for elem in self._restates
])
@util.dependencies("sqlalchemy.sql.dml")
def _populate_column_collection(self, dml):
if isinstance(self.element, dml.UpdateBase):
for col in self.element._returning:
col._make_proxy(self)
else:
for col in self.element.columns._all_columns:
col._make_proxy(self)
def alias(self, name=None, flat=False):
return CTE(
self.original,
name=name,
recursive=self.recursive,
_cte_alias=self,
_suffixes=self._suffixes
)
def union(self, other):
return CTE(
self.original.union(other),
name=self.name,
recursive=self.recursive,
_restates=self._restates.union([self]),
_suffixes=self._suffixes
)
def union_all(self, other):
return CTE(
self.original.union_all(other),
name=self.name,
recursive=self.recursive,
_restates=self._restates.union([self]),
_suffixes=self._suffixes
)
class HasCTE(object):
"""Mixin that declares a class to include CTE support.
.. versionadded:: 1.1
"""
def cte(self, name=None, recursive=False):
r"""Return a new :class:`.CTE`, or Common Table Expression instance.
Common table expressions are a SQL standard whereby SELECT
statements can draw upon secondary statements specified along
with the primary statement, using a clause called "WITH".
Special semantics regarding UNION can also be employed to
allow "recursive" queries, where a SELECT statement can draw
upon the set of rows that have previously been selected.
CTEs can also be applied to DML constructs UPDATE, INSERT
and DELETE on some databases, both as a source of CTE rows
when combined with RETURNING, as well as a consumer of
CTE rows.
SQLAlchemy detects :class:`.CTE` objects, which are treated
similarly to :class:`.Alias` objects, as special elements
to be delivered to the FROM clause of the statement as well
as to a WITH clause at the top of the statement.
.. versionchanged:: 1.1 Added support for UPDATE/INSERT/DELETE as
CTE, CTEs added to UPDATE/INSERT/DELETE.
:param name: name given to the common table expression. Like
:meth:`._FromClause.alias`, the name can be left as ``None``
in which case an anonymous symbol will be used at query
compile time.
:param recursive: if ``True``, will render ``WITH RECURSIVE``.
A recursive common table expression is intended to be used in
conjunction with UNION ALL in order to derive rows
from those already selected.
The following examples include two from PostgreSQL's documentation at
http://www.postgresql.org/docs/current/static/queries-with.html,
as well as additional examples.
Example 1, non recursive::
from sqlalchemy import (Table, Column, String, Integer,
MetaData, select, func)
metadata = MetaData()
orders = Table('orders', metadata,
Column('region', String),
Column('amount', Integer),
Column('product', String),
Column('quantity', Integer)
)
regional_sales = select([
orders.c.region,
func.sum(orders.c.amount).label('total_sales')
]).group_by(orders.c.region).cte("regional_sales")
top_regions = select([regional_sales.c.region]).\
where(
regional_sales.c.total_sales >
select([
func.sum(regional_sales.c.total_sales)/10
])
).cte("top_regions")
statement = select([
orders.c.region,
orders.c.product,
func.sum(orders.c.quantity).label("product_units"),
func.sum(orders.c.amount).label("product_sales")
]).where(orders.c.region.in_(
select([top_regions.c.region])
)).group_by(orders.c.region, orders.c.product)
result = conn.execute(statement).fetchall()
Example 2, WITH RECURSIVE::
from sqlalchemy import (Table, Column, String, Integer,
MetaData, select, func)
metadata = MetaData()
parts = Table('parts', metadata,
Column('part', String),
Column('sub_part', String),
Column('quantity', Integer),
)
included_parts = select([
parts.c.sub_part,
parts.c.part,
parts.c.quantity]).\
where(parts.c.part=='our part').\
cte(recursive=True)
incl_alias = included_parts.alias()
parts_alias = parts.alias()
included_parts = included_parts.union_all(
select([
parts_alias.c.sub_part,
parts_alias.c.part,
parts_alias.c.quantity
]).
where(parts_alias.c.part==incl_alias.c.sub_part)
)
statement = select([
included_parts.c.sub_part,
func.sum(included_parts.c.quantity).
label('total_quantity')
]).\
group_by(included_parts.c.sub_part)
result = conn.execute(statement).fetchall()
Example 3, an upsert using UPDATE and INSERT with CTEs::
from datetime import date
from sqlalchemy import (MetaData, Table, Column, Integer,
Date, select, literal, and_, exists)
metadata = MetaData()
visitors = Table('visitors', metadata,
Column('product_id', Integer, primary_key=True),
Column('date', Date, primary_key=True),
Column('count', Integer),
)
# add 5 visitors for the product_id == 1
product_id = 1
day = date.today()
count = 5
update_cte = (
visitors.update()
.where(and_(visitors.c.product_id == product_id,
visitors.c.date == day))
.values(count=visitors.c.count + count)
.returning(literal(1))
.cte('update_cte')
)
upsert = visitors.insert().from_select(
[visitors.c.product_id, visitors.c.date, visitors.c.count],
select([literal(product_id), literal(day), literal(count)])
.where(~exists(update_cte.select()))
)
connection.execute(upsert)
.. seealso::
:meth:`.orm.query.Query.cte` - ORM version of
:meth:`.HasCTE.cte`.
"""
return CTE(self, name=name, recursive=recursive)
class FromGrouping(FromClause):
"""Represent a grouping of a FROM clause"""
__visit_name__ = 'grouping'
def __init__(self, element):
self.element = element
def _init_collections(self):
pass
@property
def columns(self):
return self.element.columns
@property
def primary_key(self):
return self.element.primary_key
@property
def foreign_keys(self):
return self.element.foreign_keys
def is_derived_from(self, element):
return self.element.is_derived_from(element)
def alias(self, **kw):
return FromGrouping(self.element.alias(**kw))
@property
def _hide_froms(self):
return self.element._hide_froms
def get_children(self, **kwargs):
return self.element,
def _copy_internals(self, clone=_clone, **kw):
self.element = clone(self.element, **kw)
@property
def _from_objects(self):
return self.element._from_objects
def __getattr__(self, attr):
return getattr(self.element, attr)
def __getstate__(self):
return {'element': self.element}
def __setstate__(self, state):
self.element = state['element']
class TableClause(Immutable, FromClause):
"""Represents a minimal "table" construct.
This is a lightweight table object that has only a name and a
collection of columns, which are typically produced
by the :func:`.expression.column` function::
from sqlalchemy import table, column
user = table("user",
column("id"),
column("name"),
column("description"),
)
The :class:`.TableClause` construct serves as the base for
the more commonly used :class:`~.schema.Table` object, providing
the usual set of :class:`~.expression.FromClause` services including
the ``.c.`` collection and statement generation methods.
It does **not** provide all the additional schema-level services
of :class:`~.schema.Table`, including constraints, references to other
tables, or support for :class:`.MetaData`-level services. It's useful
on its own as an ad-hoc construct used to generate quick SQL
statements when a more fully fledged :class:`~.schema.Table`
is not on hand.
"""
__visit_name__ = 'table'
named_with_column = True
implicit_returning = False
""":class:`.TableClause` doesn't support having a primary key or column
-level defaults, so implicit returning doesn't apply."""
_autoincrement_column = None
"""No PK or default support so no autoincrement column."""
def __init__(self, name, *columns):
"""Produce a new :class:`.TableClause`.
The object returned is an instance of :class:`.TableClause`, which
represents the "syntactical" portion of the schema-level
:class:`~.schema.Table` object.
It may be used to construct lightweight table constructs.
.. versionchanged:: 1.0.0 :func:`.expression.table` can now
be imported from the plain ``sqlalchemy`` namespace like any
other SQL element.
:param name: Name of the table.
:param columns: A collection of :func:`.expression.column` constructs.
"""
super(TableClause, self).__init__()
self.name = self.fullname = name
self._columns = ColumnCollection()
self.primary_key = ColumnSet()
self.foreign_keys = set()
for c in columns:
self.append_column(c)
def _init_collections(self):
pass
@util.memoized_property
def description(self):
if util.py3k:
return self.name
else:
return self.name.encode('ascii', 'backslashreplace')
def append_column(self, c):
self._columns[c.key] = c
c.table = self
def get_children(self, column_collections=True, **kwargs):
if column_collections:
return [c for c in self.c]
else:
return []
@util.dependencies("sqlalchemy.sql.dml")
def insert(self, dml, values=None, inline=False, **kwargs):
"""Generate an :func:`.insert` construct against this
:class:`.TableClause`.
E.g.::
table.insert().values(name='foo')
See :func:`.insert` for argument and usage information.
"""
return dml.Insert(self, values=values, inline=inline, **kwargs)
@util.dependencies("sqlalchemy.sql.dml")
def update(
self, dml, whereclause=None, values=None, inline=False, **kwargs):
"""Generate an :func:`.update` construct against this
:class:`.TableClause`.
E.g.::
table.update().where(table.c.id==7).values(name='foo')
See :func:`.update` for argument and usage information.
"""
return dml.Update(self, whereclause=whereclause,
values=values, inline=inline, **kwargs)
@util.dependencies("sqlalchemy.sql.dml")
def delete(self, dml, whereclause=None, **kwargs):
"""Generate a :func:`.delete` construct against this
:class:`.TableClause`.
E.g.::
table.delete().where(table.c.id==7)
See :func:`.delete` for argument and usage information.
"""
return dml.Delete(self, whereclause, **kwargs)
@property
def _from_objects(self):
return [self]
class ForUpdateArg(ClauseElement):
@classmethod
def parse_legacy_select(self, arg):
"""Parse the for_update argument of :func:`.select`.
:param mode: Defines the lockmode to use.
``None`` - translates to no lockmode
``'update'`` - translates to ``FOR UPDATE``
(standard SQL, supported by most dialects)
``'nowait'`` - translates to ``FOR UPDATE NOWAIT``
(supported by Oracle, PostgreSQL 8.1 upwards)
``'read'`` - translates to ``LOCK IN SHARE MODE`` (for MySQL),
and ``FOR SHARE`` (for PostgreSQL)
``'read_nowait'`` - translates to ``FOR SHARE NOWAIT``
(supported by PostgreSQL). ``FOR SHARE`` and
``FOR SHARE NOWAIT`` (PostgreSQL).
"""
if arg in (None, False):
return None
nowait = read = False
if arg == 'nowait':
nowait = True
elif arg == 'read':
read = True
elif arg == 'read_nowait':
read = nowait = True
elif arg is not True:
raise exc.ArgumentError("Unknown for_update argument: %r" % arg)
return ForUpdateArg(read=read, nowait=nowait)
@property
def legacy_for_update_value(self):
if self.read and not self.nowait:
return "read"
elif self.read and self.nowait:
return "read_nowait"
elif self.nowait:
return "nowait"
else:
return True
def _copy_internals(self, clone=_clone, **kw):
if self.of is not None:
self.of = [clone(col, **kw) for col in self.of]
def __init__(
self, nowait=False, read=False, of=None,
skip_locked=False, key_share=False):
"""Represents arguments specified to :meth:`.Select.for_update`.
.. versionadded:: 0.9.0
"""
self.nowait = nowait
self.read = read
self.skip_locked = skip_locked
self.key_share = key_share
if of is not None:
self.of = [_interpret_as_column_or_from(elem)
for elem in util.to_list(of)]
else:
self.of = None
class SelectBase(HasCTE, Executable, FromClause):
"""Base class for SELECT statements.
This includes :class:`.Select`, :class:`.CompoundSelect` and
:class:`.TextAsFrom`.
"""
def as_scalar(self):
"""return a 'scalar' representation of this selectable, which can be
used as a column expression.
Typically, a select statement which has only one column in its columns
clause is eligible to be used as a scalar expression.
The returned object is an instance of
:class:`ScalarSelect`.
"""
return ScalarSelect(self)
def label(self, name):
"""return a 'scalar' representation of this selectable, embedded as a
subquery with a label.
.. seealso::
:meth:`~.SelectBase.as_scalar`.
"""
return self.as_scalar().label(name)
@_generative
@util.deprecated('0.6',
message="``autocommit()`` is deprecated. Use "
":meth:`.Executable.execution_options` with the "
"'autocommit' flag.")
def autocommit(self):
"""return a new selectable with the 'autocommit' flag set to
True.
"""
self._execution_options = \
self._execution_options.union({'autocommit': True})
def _generate(self):
"""Override the default _generate() method to also clear out
exported collections."""
s = self.__class__.__new__(self.__class__)
s.__dict__ = self.__dict__.copy()
s._reset_exported()
return s
@property
def _from_objects(self):
return [self]
class GenerativeSelect(SelectBase):
"""Base class for SELECT statements where additional elements can be
added.
This serves as the base for :class:`.Select` and :class:`.CompoundSelect`
where elements such as ORDER BY, GROUP BY can be added and column
rendering can be controlled. Compare to :class:`.TextAsFrom`, which,
while it subclasses :class:`.SelectBase` and is also a SELECT construct,
represents a fixed textual string which cannot be altered at this level,
only wrapped as a subquery.
.. versionadded:: 0.9.0 :class:`.GenerativeSelect` was added to
provide functionality specific to :class:`.Select` and
:class:`.CompoundSelect` while allowing :class:`.SelectBase` to be
used for other SELECT-like objects, e.g. :class:`.TextAsFrom`.
"""
_order_by_clause = ClauseList()
_group_by_clause = ClauseList()
_limit_clause = None
_offset_clause = None
_for_update_arg = None
def __init__(self,
use_labels=False,
for_update=False,
limit=None,
offset=None,
order_by=None,
group_by=None,
bind=None,
autocommit=None):
self.use_labels = use_labels
if for_update is not False:
self._for_update_arg = (ForUpdateArg.
parse_legacy_select(for_update))
if autocommit is not None:
util.warn_deprecated('autocommit on select() is '
'deprecated. Use .execution_options(a'
'utocommit=True)')
self._execution_options = \
self._execution_options.union(
{'autocommit': autocommit})
if limit is not None:
self._limit_clause = _offset_or_limit_clause(limit)
if offset is not None:
self._offset_clause = _offset_or_limit_clause(offset)
self._bind = bind
if order_by is not None:
self._order_by_clause = ClauseList(
*util.to_list(order_by),
_literal_as_text=_literal_and_labels_as_label_reference)
if group_by is not None:
self._group_by_clause = ClauseList(
*util.to_list(group_by),
_literal_as_text=_literal_as_label_reference)
@property
def for_update(self):
"""Provide legacy dialect support for the ``for_update`` attribute.
"""
if self._for_update_arg is not None:
return self._for_update_arg.legacy_for_update_value
else:
return None
@for_update.setter
def for_update(self, value):
self._for_update_arg = ForUpdateArg.parse_legacy_select(value)
@_generative
def with_for_update(self, nowait=False, read=False, of=None,
skip_locked=False, key_share=False):
"""Specify a ``FOR UPDATE`` clause for this :class:`.GenerativeSelect`.
E.g.::
stmt = select([table]).with_for_update(nowait=True)
On a database like PostgreSQL or Oracle, the above would render a
statement like::
SELECT table.a, table.b FROM table FOR UPDATE NOWAIT
on other backends, the ``nowait`` option is ignored and instead
would produce::
SELECT table.a, table.b FROM table FOR UPDATE
When called with no arguments, the statement will render with
the suffix ``FOR UPDATE``. Additional arguments can then be
provided which allow for common database-specific
variants.
:param nowait: boolean; will render ``FOR UPDATE NOWAIT`` on Oracle
and PostgreSQL dialects.
:param read: boolean; will render ``LOCK IN SHARE MODE`` on MySQL,
``FOR SHARE`` on PostgreSQL. On PostgreSQL, when combined with
``nowait``, will render ``FOR SHARE NOWAIT``.
:param of: SQL expression or list of SQL expression elements
(typically :class:`.Column` objects or a compatible expression) which
will render into a ``FOR UPDATE OF`` clause; supported by PostgreSQL
and Oracle. May render as a table or as a column depending on
backend.
:param skip_locked: boolean, will render ``FOR UPDATE SKIP LOCKED``
on Oracle and PostgreSQL dialects or ``FOR SHARE SKIP LOCKED`` if
``read=True`` is also specified.
.. versionadded:: 1.1.0
:param key_share: boolean, will render ``FOR NO KEY UPDATE``,
or if combined with ``read=True`` will render ``FOR KEY SHARE``,
on the PostgreSQL dialect.
.. versionadded:: 1.1.0
"""
self._for_update_arg = ForUpdateArg(nowait=nowait, read=read, of=of,
skip_locked=skip_locked,
key_share=key_share)
@_generative
def apply_labels(self):
"""return a new selectable with the 'use_labels' flag set to True.
This will result in column expressions being generated using labels
against their table name, such as "SELECT somecolumn AS
tablename_somecolumn". This allows selectables which contain multiple
FROM clauses to produce a unique set of column names regardless of
name conflicts among the individual FROM clauses.
"""
self.use_labels = True
@property
def _limit(self):
"""Get an integer value for the limit. This should only be used
by code that cannot support a limit as a BindParameter or
other custom clause as it will throw an exception if the limit
isn't currently set to an integer.
"""
return _offset_or_limit_clause_asint(self._limit_clause, "limit")
@property
def _simple_int_limit(self):
"""True if the LIMIT clause is a simple integer, False
if it is not present or is a SQL expression.
"""
return isinstance(self._limit_clause, _OffsetLimitParam)
@property
def _simple_int_offset(self):
"""True if the OFFSET clause is a simple integer, False
if it is not present or is a SQL expression.
"""
return isinstance(self._offset_clause, _OffsetLimitParam)
@property
def _offset(self):
"""Get an integer value for the offset. This should only be used
by code that cannot support an offset as a BindParameter or
other custom clause as it will throw an exception if the
offset isn't currently set to an integer.
"""
return _offset_or_limit_clause_asint(self._offset_clause, "offset")
@_generative
def limit(self, limit):
"""return a new selectable with the given LIMIT criterion
applied.
This is a numerical value which usually renders as a ``LIMIT``
expression in the resulting select. Backends that don't
support ``LIMIT`` will attempt to provide similar
functionality.
.. versionchanged:: 1.0.0 - :meth:`.Select.limit` can now
accept arbitrary SQL expressions as well as integer values.
:param limit: an integer LIMIT parameter, or a SQL expression
that provides an integer result.
"""
self._limit_clause = _offset_or_limit_clause(limit)
@_generative
def offset(self, offset):
"""return a new selectable with the given OFFSET criterion
applied.
This is a numeric value which usually renders as an ``OFFSET``
expression in the resulting select. Backends that don't
support ``OFFSET`` will attempt to provide similar
functionality.
.. versionchanged:: 1.0.0 - :meth:`.Select.offset` can now
accept arbitrary SQL expressions as well as integer values.
:param offset: an integer OFFSET parameter, or a SQL expression
that provides an integer result.
"""
self._offset_clause = _offset_or_limit_clause(offset)
@_generative
def order_by(self, *clauses):
"""return a new selectable with the given list of ORDER BY
criterion applied.
The criterion will be appended to any pre-existing ORDER BY
criterion.
"""
self.append_order_by(*clauses)
@_generative
def group_by(self, *clauses):
"""return a new selectable with the given list of GROUP BY
criterion applied.
The criterion will be appended to any pre-existing GROUP BY
criterion.
"""
self.append_group_by(*clauses)
def append_order_by(self, *clauses):
"""Append the given ORDER BY criterion applied to this selectable.
The criterion will be appended to any pre-existing ORDER BY criterion.
This is an **in-place** mutation method; the
:meth:`~.GenerativeSelect.order_by` method is preferred, as it
provides standard :term:`method chaining`.
"""
if len(clauses) == 1 and clauses[0] is None:
self._order_by_clause = ClauseList()
else:
if getattr(self, '_order_by_clause', None) is not None:
clauses = list(self._order_by_clause) + list(clauses)
self._order_by_clause = ClauseList(
*clauses,
_literal_as_text=_literal_and_labels_as_label_reference)
def append_group_by(self, *clauses):
"""Append the given GROUP BY criterion applied to this selectable.
The criterion will be appended to any pre-existing GROUP BY criterion.
This is an **in-place** mutation method; the
:meth:`~.GenerativeSelect.group_by` method is preferred, as it
provides standard :term:`method chaining`.
"""
if len(clauses) == 1 and clauses[0] is None:
self._group_by_clause = ClauseList()
else:
if getattr(self, '_group_by_clause', None) is not None:
clauses = list(self._group_by_clause) + list(clauses)
self._group_by_clause = ClauseList(
*clauses, _literal_as_text=_literal_as_label_reference)
@property
def _label_resolve_dict(self):
raise NotImplementedError()
def _copy_internals(self, clone=_clone, **kw):
if self._limit_clause is not None:
self._limit_clause = clone(self._limit_clause, **kw)
if self._offset_clause is not None:
self._offset_clause = clone(self._offset_clause, **kw)
class CompoundSelect(GenerativeSelect):
"""Forms the basis of ``UNION``, ``UNION ALL``, and other
SELECT-based set operations.
.. seealso::
:func:`.union`
:func:`.union_all`
:func:`.intersect`
:func:`.intersect_all`
:func:`.except`
:func:`.except_all`
"""
__visit_name__ = 'compound_select'
UNION = util.symbol('UNION')
UNION_ALL = util.symbol('UNION ALL')
EXCEPT = util.symbol('EXCEPT')
EXCEPT_ALL = util.symbol('EXCEPT ALL')
INTERSECT = util.symbol('INTERSECT')
INTERSECT_ALL = util.symbol('INTERSECT ALL')
_is_from_container = True
def __init__(self, keyword, *selects, **kwargs):
self._auto_correlate = kwargs.pop('correlate', False)
self.keyword = keyword
self.selects = []
numcols = None
# some DBs do not like ORDER BY in the inner queries of a UNION, etc.
for n, s in enumerate(selects):
s = _clause_element_as_expr(s)
if not numcols:
numcols = len(s.c._all_columns)
elif len(s.c._all_columns) != numcols:
raise exc.ArgumentError(
'All selectables passed to '
'CompoundSelect must have identical numbers of '
'columns; select #%d has %d columns, select '
'#%d has %d' %
(1, len(self.selects[0].c._all_columns),
n + 1, len(s.c._all_columns))
)
self.selects.append(s.self_group(self))
GenerativeSelect.__init__(self, **kwargs)
@property
def _label_resolve_dict(self):
d = dict(
(c.key, c) for c in self.c
)
return d, d, d
@classmethod
def _create_union(cls, *selects, **kwargs):
r"""Return a ``UNION`` of multiple selectables.
The returned object is an instance of
:class:`.CompoundSelect`.
A similar :func:`union()` method is available on all
:class:`.FromClause` subclasses.
\*selects
a list of :class:`.Select` instances.
\**kwargs
available keyword arguments are the same as those of
:func:`select`.
"""
return CompoundSelect(CompoundSelect.UNION, *selects, **kwargs)
@classmethod
def _create_union_all(cls, *selects, **kwargs):
r"""Return a ``UNION ALL`` of multiple selectables.
The returned object is an instance of
:class:`.CompoundSelect`.
A similar :func:`union_all()` method is available on all
:class:`.FromClause` subclasses.
\*selects
a list of :class:`.Select` instances.
\**kwargs
available keyword arguments are the same as those of
:func:`select`.
"""
return CompoundSelect(CompoundSelect.UNION_ALL, *selects, **kwargs)
@classmethod
def _create_except(cls, *selects, **kwargs):
r"""Return an ``EXCEPT`` of multiple selectables.
The returned object is an instance of
:class:`.CompoundSelect`.
\*selects
a list of :class:`.Select` instances.
\**kwargs
available keyword arguments are the same as those of
:func:`select`.
"""
return CompoundSelect(CompoundSelect.EXCEPT, *selects, **kwargs)
@classmethod
def _create_except_all(cls, *selects, **kwargs):
r"""Return an ``EXCEPT ALL`` of multiple selectables.
The returned object is an instance of
:class:`.CompoundSelect`.
\*selects
a list of :class:`.Select` instances.
\**kwargs
available keyword arguments are the same as those of
:func:`select`.
"""
return CompoundSelect(CompoundSelect.EXCEPT_ALL, *selects, **kwargs)
@classmethod
def _create_intersect(cls, *selects, **kwargs):
r"""Return an ``INTERSECT`` of multiple selectables.
The returned object is an instance of
:class:`.CompoundSelect`.
\*selects
a list of :class:`.Select` instances.
\**kwargs
available keyword arguments are the same as those of
:func:`select`.
"""
return CompoundSelect(CompoundSelect.INTERSECT, *selects, **kwargs)
@classmethod
def _create_intersect_all(cls, *selects, **kwargs):
r"""Return an ``INTERSECT ALL`` of multiple selectables.
The returned object is an instance of
:class:`.CompoundSelect`.
\*selects
a list of :class:`.Select` instances.
\**kwargs
available keyword arguments are the same as those of
:func:`select`.
"""
return CompoundSelect(
CompoundSelect.INTERSECT_ALL, *selects, **kwargs)
def _scalar_type(self):
return self.selects[0]._scalar_type()
def self_group(self, against=None):
return FromGrouping(self)
def is_derived_from(self, fromclause):
for s in self.selects:
if s.is_derived_from(fromclause):
return True
return False
def _populate_column_collection(self):
for cols in zip(*[s.c._all_columns for s in self.selects]):
# this is a slightly hacky thing - the union exports a
# column that resembles just that of the *first* selectable.
# to get at a "composite" column, particularly foreign keys,
# you have to dig through the proxies collection which we
# generate below. We may want to improve upon this, such as
# perhaps _make_proxy can accept a list of other columns
# that are "shared" - schema.column can then copy all the
# ForeignKeys in. this would allow the union() to have all
# those fks too.
proxy = cols[0]._make_proxy(
self, name=cols[0]._label if self.use_labels else None,
key=cols[0]._key_label if self.use_labels else None)
# hand-construct the "_proxies" collection to include all
# derived columns place a 'weight' annotation corresponding
# to how low in the list of select()s the column occurs, so
# that the corresponding_column() operation can resolve
# conflicts
proxy._proxies = [
c._annotate({'weight': i + 1}) for (i, c) in enumerate(cols)]
def _refresh_for_new_column(self, column):
for s in self.selects:
s._refresh_for_new_column(column)
if not self._cols_populated:
return None
raise NotImplementedError("CompoundSelect constructs don't support "
"addition of columns to underlying "
"selectables")
def _copy_internals(self, clone=_clone, **kw):
super(CompoundSelect, self)._copy_internals(clone, **kw)
self._reset_exported()
self.selects = [clone(s, **kw) for s in self.selects]
if hasattr(self, '_col_map'):
del self._col_map
for attr in (
'_order_by_clause', '_group_by_clause', '_for_update_arg'):
if getattr(self, attr) is not None:
setattr(self, attr, clone(getattr(self, attr), **kw))
def get_children(self, column_collections=True, **kwargs):
return (column_collections and list(self.c) or []) \
+ [self._order_by_clause, self._group_by_clause] \
+ list(self.selects)
def bind(self):
if self._bind:
return self._bind
for s in self.selects:
e = s.bind
if e:
return e
else:
return None
def _set_bind(self, bind):
self._bind = bind
bind = property(bind, _set_bind)
class Select(HasPrefixes, HasSuffixes, GenerativeSelect):
"""Represents a ``SELECT`` statement.
"""
__visit_name__ = 'select'
_prefixes = ()
_suffixes = ()
_hints = util.immutabledict()
_statement_hints = ()
_distinct = False
_from_cloned = None
_correlate = ()
_correlate_except = None
_memoized_property = SelectBase._memoized_property
_is_select = True
def __init__(self,
columns=None,
whereclause=None,
from_obj=None,
distinct=False,
having=None,
correlate=True,
prefixes=None,
suffixes=None,
**kwargs):
"""Construct a new :class:`.Select`.
Similar functionality is also available via the
:meth:`.FromClause.select` method on any :class:`.FromClause`.
All arguments which accept :class:`.ClauseElement` arguments also
accept string arguments, which will be converted as appropriate into
either :func:`text()` or :func:`literal_column()` constructs.
.. seealso::
:ref:`coretutorial_selecting` - Core Tutorial description of
:func:`.select`.
:param columns:
A list of :class:`.ColumnElement` or :class:`.FromClause`
objects which will form the columns clause of the resulting
statement. For those objects that are instances of
:class:`.FromClause` (typically :class:`.Table` or :class:`.Alias`
objects), the :attr:`.FromClause.c` collection is extracted
to form a collection of :class:`.ColumnElement` objects.
This parameter will also accept :class:`.Text` constructs as
given, as well as ORM-mapped classes.
.. note::
The :paramref:`.select.columns` parameter is not available
in the method form of :func:`.select`, e.g.
:meth:`.FromClause.select`.
.. seealso::
:meth:`.Select.column`
:meth:`.Select.with_only_columns`
:param whereclause:
A :class:`.ClauseElement` expression which will be used to form the
``WHERE`` clause. It is typically preferable to add WHERE
criterion to an existing :class:`.Select` using method chaining
with :meth:`.Select.where`.
.. seealso::
:meth:`.Select.where`
:param from_obj:
A list of :class:`.ClauseElement` objects which will be added to the
``FROM`` clause of the resulting statement. This is equivalent
to calling :meth:`.Select.select_from` using method chaining on
an existing :class:`.Select` object.
.. seealso::
:meth:`.Select.select_from` - full description of explicit
FROM clause specification.
:param autocommit:
Deprecated. Use ``.execution_options(autocommit=<True|False>)``
to set the autocommit option.
.. seealso::
:meth:`.Executable.execution_options`
:param bind=None:
an :class:`~.Engine` or :class:`~.Connection` instance
to which the
resulting :class:`.Select` object will be bound. The
:class:`.Select` object will otherwise automatically bind to
whatever :class:`~.base.Connectable` instances can be located within
its contained :class:`.ClauseElement` members.
:param correlate=True:
indicates that this :class:`.Select` object should have its
contained :class:`.FromClause` elements "correlated" to an enclosing
:class:`.Select` object. It is typically preferable to specify
correlations on an existing :class:`.Select` construct using
:meth:`.Select.correlate`.
.. seealso::
:meth:`.Select.correlate` - full description of correlation.
:param distinct=False:
when ``True``, applies a ``DISTINCT`` qualifier to the columns
clause of the resulting statement.
The boolean argument may also be a column expression or list
of column expressions - this is a special calling form which
is understood by the PostgreSQL dialect to render the
``DISTINCT ON (<columns>)`` syntax.
``distinct`` is also available on an existing :class:`.Select`
object via the :meth:`~.Select.distinct` method.
.. seealso::
:meth:`.Select.distinct`
:param for_update=False:
when ``True``, applies ``FOR UPDATE`` to the end of the
resulting statement.
.. deprecated:: 0.9.0 - use
:meth:`.Select.with_for_update` to specify the
structure of the ``FOR UPDATE`` clause.
``for_update`` accepts various string values interpreted by
specific backends, including:
* ``"read"`` - on MySQL, translates to ``LOCK IN SHARE MODE``;
on PostgreSQL, translates to ``FOR SHARE``.
* ``"nowait"`` - on PostgreSQL and Oracle, translates to
``FOR UPDATE NOWAIT``.
* ``"read_nowait"`` - on PostgreSQL, translates to
``FOR SHARE NOWAIT``.
.. seealso::
:meth:`.Select.with_for_update` - improved API for
specifying the ``FOR UPDATE`` clause.
:param group_by:
a list of :class:`.ClauseElement` objects which will comprise the
``GROUP BY`` clause of the resulting select. This parameter
is typically specified more naturally using the
:meth:`.Select.group_by` method on an existing :class:`.Select`.
.. seealso::
:meth:`.Select.group_by`
:param having:
a :class:`.ClauseElement` that will comprise the ``HAVING`` clause
of the resulting select when ``GROUP BY`` is used. This parameter
is typically specified more naturally using the
:meth:`.Select.having` method on an existing :class:`.Select`.
.. seealso::
:meth:`.Select.having`
:param limit=None:
a numerical value which usually renders as a ``LIMIT``
expression in the resulting select. Backends that don't
support ``LIMIT`` will attempt to provide similar
functionality. This parameter is typically specified more naturally
using the :meth:`.Select.limit` method on an existing
:class:`.Select`.
.. seealso::
:meth:`.Select.limit`
:param offset=None:
a numeric value which usually renders as an ``OFFSET``
expression in the resulting select. Backends that don't
support ``OFFSET`` will attempt to provide similar
functionality. This parameter is typically specified more naturally
using the :meth:`.Select.offset` method on an existing
:class:`.Select`.
.. seealso::
:meth:`.Select.offset`
:param order_by:
a scalar or list of :class:`.ClauseElement` objects which will
comprise the ``ORDER BY`` clause of the resulting select.
This parameter is typically specified more naturally using the
:meth:`.Select.order_by` method on an existing :class:`.Select`.
.. seealso::
:meth:`.Select.order_by`
:param use_labels=False:
when ``True``, the statement will be generated using labels
for each column in the columns clause, which qualify each
column with its parent table's (or aliases) name so that name
conflicts between columns in different tables don't occur.
The format of the label is <tablename>_<column>. The "c"
collection of the resulting :class:`.Select` object will use these
names as well for targeting column members.
This parameter can also be specified on an existing
:class:`.Select` object using the :meth:`.Select.apply_labels`
method.
.. seealso::
:meth:`.Select.apply_labels`
"""
self._auto_correlate = correlate
if distinct is not False:
if distinct is True:
self._distinct = True
else:
self._distinct = [
_literal_as_text(e)
for e in util.to_list(distinct)
]
if from_obj is not None:
self._from_obj = util.OrderedSet(
_interpret_as_from(f)
for f in util.to_list(from_obj))
else:
self._from_obj = util.OrderedSet()
try:
cols_present = bool(columns)
except TypeError:
raise exc.ArgumentError("columns argument to select() must "
"be a Python list or other iterable")
if cols_present:
self._raw_columns = []
for c in columns:
c = _interpret_as_column_or_from(c)
if isinstance(c, ScalarSelect):
c = c.self_group(against=operators.comma_op)
self._raw_columns.append(c)
else:
self._raw_columns = []
if whereclause is not None:
self._whereclause = _literal_as_text(
whereclause).self_group(against=operators._asbool)
else:
self._whereclause = None
if having is not None:
self._having = _literal_as_text(
having).self_group(against=operators._asbool)
else:
self._having = None
if prefixes:
self._setup_prefixes(prefixes)
if suffixes:
self._setup_suffixes(suffixes)
GenerativeSelect.__init__(self, **kwargs)
@property
def _froms(self):
# would love to cache this,
# but there's just enough edge cases, particularly now that
# declarative encourages construction of SQL expressions
# without tables present, to just regen this each time.
froms = []
seen = set()
translate = self._from_cloned
for item in itertools.chain(
_from_objects(*self._raw_columns),
_from_objects(self._whereclause)
if self._whereclause is not None else (),
self._from_obj
):
if item is self:
raise exc.InvalidRequestError(
"select() construct refers to itself as a FROM")
if translate and item in translate:
item = translate[item]
if not seen.intersection(item._cloned_set):
froms.append(item)
seen.update(item._cloned_set)
return froms
def _get_display_froms(self, explicit_correlate_froms=None,
implicit_correlate_froms=None):
"""Return the full list of 'from' clauses to be displayed.
Takes into account a set of existing froms which may be
rendered in the FROM clause of enclosing selects; this Select
may want to leave those absent if it is automatically
correlating.
"""
froms = self._froms
toremove = set(itertools.chain(*[
_expand_cloned(f._hide_froms)
for f in froms]))
if toremove:
# if we're maintaining clones of froms,
# add the copies out to the toremove list. only include
# clones that are lexical equivalents.
if self._from_cloned:
toremove.update(
self._from_cloned[f] for f in
toremove.intersection(self._from_cloned)
if self._from_cloned[f]._is_lexical_equivalent(f)
)
# filter out to FROM clauses not in the list,
# using a list to maintain ordering
froms = [f for f in froms if f not in toremove]
if self._correlate:
to_correlate = self._correlate
if to_correlate:
froms = [
f for f in froms if f not in
_cloned_intersection(
_cloned_intersection(
froms, explicit_correlate_froms or ()),
to_correlate
)
]
if self._correlate_except is not None:
froms = [
f for f in froms if f not in
_cloned_difference(
_cloned_intersection(
froms, explicit_correlate_froms or ()),
self._correlate_except
)
]
if self._auto_correlate and \
implicit_correlate_froms and \
len(froms) > 1:
froms = [
f for f in froms if f not in
_cloned_intersection(froms, implicit_correlate_froms)
]
if not len(froms):
raise exc.InvalidRequestError("Select statement '%s"
"' returned no FROM clauses "
"due to auto-correlation; "
"specify correlate(<tables>) "
"to control correlation "
"manually." % self)
return froms
def _scalar_type(self):
elem = self._raw_columns[0]
cols = list(elem._select_iterable)
return cols[0].type
@property
def froms(self):
"""Return the displayed list of FromClause elements."""
return self._get_display_froms()
def with_statement_hint(self, text, dialect_name='*'):
"""add a statement hint to this :class:`.Select`.
This method is similar to :meth:`.Select.with_hint` except that
it does not require an individual table, and instead applies to the
statement as a whole.
Hints here are specific to the backend database and may include
directives such as isolation levels, file directives, fetch directives,
etc.
.. versionadded:: 1.0.0
.. seealso::
:meth:`.Select.with_hint`
"""
return self.with_hint(None, text, dialect_name)
@_generative
def with_hint(self, selectable, text, dialect_name='*'):
r"""Add an indexing or other executional context hint for the given
selectable to this :class:`.Select`.
The text of the hint is rendered in the appropriate
location for the database backend in use, relative
to the given :class:`.Table` or :class:`.Alias` passed as the
``selectable`` argument. The dialect implementation
typically uses Python string substitution syntax
with the token ``%(name)s`` to render the name of
the table or alias. E.g. when using Oracle, the
following::
select([mytable]).\
with_hint(mytable, "index(%(name)s ix_mytable)")
Would render SQL as::
select /*+ index(mytable ix_mytable) */ ... from mytable
The ``dialect_name`` option will limit the rendering of a particular
hint to a particular backend. Such as, to add hints for both Oracle
and Sybase simultaneously::
select([mytable]).\
with_hint(mytable, "index(%(name)s ix_mytable)", 'oracle').\
with_hint(mytable, "WITH INDEX ix_mytable", 'sybase')
.. seealso::
:meth:`.Select.with_statement_hint`
"""
if selectable is None:
self._statement_hints += ((dialect_name, text), )
else:
self._hints = self._hints.union(
{(selectable, dialect_name): text})
@property
def type(self):
raise exc.InvalidRequestError("Select objects don't have a type. "
"Call as_scalar() on this Select "
"object to return a 'scalar' version "
"of this Select.")
@_memoized_property.method
def locate_all_froms(self):
"""return a Set of all FromClause elements referenced by this Select.
This set is a superset of that returned by the ``froms`` property,
which is specifically for those FromClause elements that would
actually be rendered.
"""
froms = self._froms
return froms + list(_from_objects(*froms))
@property
def inner_columns(self):
"""an iterator of all ColumnElement expressions which would
be rendered into the columns clause of the resulting SELECT statement.
"""
return _select_iterables(self._raw_columns)
@_memoized_property
def _label_resolve_dict(self):
with_cols = dict(
(c._resolve_label or c._label or c.key, c)
for c in _select_iterables(self._raw_columns)
if c._allow_label_resolve)
only_froms = dict(
(c.key, c) for c in
_select_iterables(self.froms) if c._allow_label_resolve)
only_cols = with_cols.copy()
for key, value in only_froms.items():
with_cols.setdefault(key, value)
return with_cols, only_froms, only_cols
def is_derived_from(self, fromclause):
if self in fromclause._cloned_set:
return True
for f in self.locate_all_froms():
if f.is_derived_from(fromclause):
return True
return False
def _copy_internals(self, clone=_clone, **kw):
super(Select, self)._copy_internals(clone, **kw)
# Select() object has been cloned and probably adapted by the
# given clone function. Apply the cloning function to internal
# objects
# 1. keep a dictionary of the froms we've cloned, and what
# they've become. This is consulted later when we derive
# additional froms from "whereclause" and the columns clause,
# which may still reference the uncloned parent table.
# as of 0.7.4 we also put the current version of _froms, which
# gets cleared on each generation. previously we were "baking"
# _froms into self._from_obj.
self._from_cloned = from_cloned = dict(
(f, clone(f, **kw)) for f in self._from_obj.union(self._froms))
# 3. update persistent _from_obj with the cloned versions.
self._from_obj = util.OrderedSet(from_cloned[f] for f in
self._from_obj)
# the _correlate collection is done separately, what can happen
# here is the same item is _correlate as in _from_obj but the
# _correlate version has an annotation on it - (specifically
# RelationshipProperty.Comparator._criterion_exists() does
# this). Also keep _correlate liberally open with its previous
# contents, as this set is used for matching, not rendering.
self._correlate = set(clone(f) for f in
self._correlate).union(self._correlate)
# 4. clone other things. The difficulty here is that Column
# objects are not actually cloned, and refer to their original
# .table, resulting in the wrong "from" parent after a clone
# operation. Hence _from_cloned and _from_obj supersede what is
# present here.
self._raw_columns = [clone(c, **kw) for c in self._raw_columns]
for attr in '_whereclause', '_having', '_order_by_clause', \
'_group_by_clause', '_for_update_arg':
if getattr(self, attr) is not None:
setattr(self, attr, clone(getattr(self, attr), **kw))
# erase exported column list, _froms collection,
# etc.
self._reset_exported()
def get_children(self, column_collections=True, **kwargs):
"""return child elements as per the ClauseElement specification."""
return (column_collections and list(self.columns) or []) + \
self._raw_columns + list(self._froms) + \
[x for x in
(self._whereclause, self._having,
self._order_by_clause, self._group_by_clause)
if x is not None]
@_generative
def column(self, column):
"""return a new select() construct with the given column expression
added to its columns clause.
"""
self.append_column(column)
@util.dependencies("sqlalchemy.sql.util")
def reduce_columns(self, sqlutil, only_synonyms=True):
"""Return a new :func`.select` construct with redundantly
named, equivalently-valued columns removed from the columns clause.
"Redundant" here means two columns where one refers to the
other either based on foreign key, or via a simple equality
comparison in the WHERE clause of the statement. The primary purpose
of this method is to automatically construct a select statement
with all uniquely-named columns, without the need to use
table-qualified labels as :meth:`.apply_labels` does.
When columns are omitted based on foreign key, the referred-to
column is the one that's kept. When columns are omitted based on
WHERE eqivalence, the first column in the columns clause is the
one that's kept.
:param only_synonyms: when True, limit the removal of columns
to those which have the same name as the equivalent. Otherwise,
all columns that are equivalent to another are removed.
.. versionadded:: 0.8
"""
return self.with_only_columns(
sqlutil.reduce_columns(
self.inner_columns,
only_synonyms=only_synonyms,
*(self._whereclause, ) + tuple(self._from_obj)
)
)
@_generative
def with_only_columns(self, columns):
r"""Return a new :func:`.select` construct with its columns
clause replaced with the given columns.
.. versionchanged:: 0.7.3
Due to a bug fix, this method has a slight
behavioral change as of version 0.7.3.
Prior to version 0.7.3, the FROM clause of
a :func:`.select` was calculated upfront and as new columns
were added; in 0.7.3 and later it's calculated
at compile time, fixing an issue regarding late binding
of columns to parent tables. This changes the behavior of
:meth:`.Select.with_only_columns` in that FROM clauses no
longer represented in the new list are dropped,
but this behavior is more consistent in
that the FROM clauses are consistently derived from the
current columns clause. The original intent of this method
is to allow trimming of the existing columns list to be fewer
columns than originally present; the use case of replacing
the columns list with an entirely different one hadn't
been anticipated until 0.7.3 was released; the usage
guidelines below illustrate how this should be done.
This method is exactly equivalent to as if the original
:func:`.select` had been called with the given columns
clause. I.e. a statement::
s = select([table1.c.a, table1.c.b])
s = s.with_only_columns([table1.c.b])
should be exactly equivalent to::
s = select([table1.c.b])
This means that FROM clauses which are only derived
from the column list will be discarded if the new column
list no longer contains that FROM::
>>> table1 = table('t1', column('a'), column('b'))
>>> table2 = table('t2', column('a'), column('b'))
>>> s1 = select([table1.c.a, table2.c.b])
>>> print s1
SELECT t1.a, t2.b FROM t1, t2
>>> s2 = s1.with_only_columns([table2.c.b])
>>> print s2
SELECT t2.b FROM t1
The preferred way to maintain a specific FROM clause
in the construct, assuming it won't be represented anywhere
else (i.e. not in the WHERE clause, etc.) is to set it using
:meth:`.Select.select_from`::
>>> s1 = select([table1.c.a, table2.c.b]).\
... select_from(table1.join(table2,
... table1.c.a==table2.c.a))
>>> s2 = s1.with_only_columns([table2.c.b])
>>> print s2
SELECT t2.b FROM t1 JOIN t2 ON t1.a=t2.a
Care should also be taken to use the correct
set of column objects passed to :meth:`.Select.with_only_columns`.
Since the method is essentially equivalent to calling the
:func:`.select` construct in the first place with the given
columns, the columns passed to :meth:`.Select.with_only_columns`
should usually be a subset of those which were passed
to the :func:`.select` construct, not those which are available
from the ``.c`` collection of that :func:`.select`. That
is::
s = select([table1.c.a, table1.c.b]).select_from(table1)
s = s.with_only_columns([table1.c.b])
and **not**::
# usually incorrect
s = s.with_only_columns([s.c.b])
The latter would produce the SQL::
SELECT b
FROM (SELECT t1.a AS a, t1.b AS b
FROM t1), t1
Since the :func:`.select` construct is essentially being
asked to select both from ``table1`` as well as itself.
"""
self._reset_exported()
rc = []
for c in columns:
c = _interpret_as_column_or_from(c)
if isinstance(c, ScalarSelect):
c = c.self_group(against=operators.comma_op)
rc.append(c)
self._raw_columns = rc
@_generative
def where(self, whereclause):
"""return a new select() construct with the given expression added to
its WHERE clause, joined to the existing clause via AND, if any.
"""
self.append_whereclause(whereclause)
@_generative
def having(self, having):
"""return a new select() construct with the given expression added to
its HAVING clause, joined to the existing clause via AND, if any.
"""
self.append_having(having)
@_generative
def distinct(self, *expr):
r"""Return a new select() construct which will apply DISTINCT to its
columns clause.
:param \*expr: optional column expressions. When present,
the PostgreSQL dialect will render a ``DISTINCT ON (<expressions>>)``
construct.
"""
if expr:
expr = [_literal_as_label_reference(e) for e in expr]
if isinstance(self._distinct, list):
self._distinct = self._distinct + expr
else:
self._distinct = expr
else:
self._distinct = True
@_generative
def select_from(self, fromclause):
r"""return a new :func:`.select` construct with the
given FROM expression
merged into its list of FROM objects.
E.g.::
table1 = table('t1', column('a'))
table2 = table('t2', column('b'))
s = select([table1.c.a]).\
select_from(
table1.join(table2, table1.c.a==table2.c.b)
)
The "from" list is a unique set on the identity of each element,
so adding an already present :class:`.Table` or other selectable
will have no effect. Passing a :class:`.Join` that refers
to an already present :class:`.Table` or other selectable will have
the effect of concealing the presence of that selectable as
an individual element in the rendered FROM list, instead
rendering it into a JOIN clause.
While the typical purpose of :meth:`.Select.select_from` is to
replace the default, derived FROM clause with a join, it can
also be called with individual table elements, multiple times
if desired, in the case that the FROM clause cannot be fully
derived from the columns clause::
select([func.count('*')]).select_from(table1)
"""
self.append_from(fromclause)
@_generative
def correlate(self, *fromclauses):
r"""return a new :class:`.Select` which will correlate the given FROM
clauses to that of an enclosing :class:`.Select`.
Calling this method turns off the :class:`.Select` object's
default behavior of "auto-correlation". Normally, FROM elements
which appear in a :class:`.Select` that encloses this one via
its :term:`WHERE clause`, ORDER BY, HAVING or
:term:`columns clause` will be omitted from this :class:`.Select`
object's :term:`FROM clause`.
Setting an explicit correlation collection using the
:meth:`.Select.correlate` method provides a fixed list of FROM objects
that can potentially take place in this process.
When :meth:`.Select.correlate` is used to apply specific FROM clauses
for correlation, the FROM elements become candidates for
correlation regardless of how deeply nested this :class:`.Select`
object is, relative to an enclosing :class:`.Select` which refers to
the same FROM object. This is in contrast to the behavior of
"auto-correlation" which only correlates to an immediate enclosing
:class:`.Select`. Multi-level correlation ensures that the link
between enclosed and enclosing :class:`.Select` is always via
at least one WHERE/ORDER BY/HAVING/columns clause in order for
correlation to take place.
If ``None`` is passed, the :class:`.Select` object will correlate
none of its FROM entries, and all will render unconditionally
in the local FROM clause.
:param \*fromclauses: a list of one or more :class:`.FromClause`
constructs, or other compatible constructs (i.e. ORM-mapped
classes) to become part of the correlate collection.
.. versionchanged:: 0.8.0 ORM-mapped classes are accepted by
:meth:`.Select.correlate`.
.. versionchanged:: 0.8.0 The :meth:`.Select.correlate` method no
longer unconditionally removes entries from the FROM clause;
instead, the candidate FROM entries must also be matched by a FROM
entry located in an enclosing :class:`.Select`, which ultimately
encloses this one as present in the WHERE clause, ORDER BY clause,
HAVING clause, or columns clause of an enclosing :meth:`.Select`.
.. versionchanged:: 0.8.2 explicit correlation takes place
via any level of nesting of :class:`.Select` objects; in previous
0.8 versions, correlation would only occur relative to the
immediate enclosing :class:`.Select` construct.
.. seealso::
:meth:`.Select.correlate_except`
:ref:`correlated_subqueries`
"""
self._auto_correlate = False
if fromclauses and fromclauses[0] is None:
self._correlate = ()
else:
self._correlate = set(self._correlate).union(
_interpret_as_from(f) for f in fromclauses)
@_generative
def correlate_except(self, *fromclauses):
r"""return a new :class:`.Select` which will omit the given FROM
clauses from the auto-correlation process.
Calling :meth:`.Select.correlate_except` turns off the
:class:`.Select` object's default behavior of
"auto-correlation" for the given FROM elements. An element
specified here will unconditionally appear in the FROM list, while
all other FROM elements remain subject to normal auto-correlation
behaviors.
.. versionchanged:: 0.8.2 The :meth:`.Select.correlate_except`
method was improved to fully prevent FROM clauses specified here
from being omitted from the immediate FROM clause of this
:class:`.Select`.
If ``None`` is passed, the :class:`.Select` object will correlate
all of its FROM entries.
.. versionchanged:: 0.8.2 calling ``correlate_except(None)`` will
correctly auto-correlate all FROM clauses.
:param \*fromclauses: a list of one or more :class:`.FromClause`
constructs, or other compatible constructs (i.e. ORM-mapped
classes) to become part of the correlate-exception collection.
.. seealso::
:meth:`.Select.correlate`
:ref:`correlated_subqueries`
"""
self._auto_correlate = False
if fromclauses and fromclauses[0] is None:
self._correlate_except = ()
else:
self._correlate_except = set(self._correlate_except or ()).union(
_interpret_as_from(f) for f in fromclauses)
def append_correlation(self, fromclause):
"""append the given correlation expression to this select()
construct.
This is an **in-place** mutation method; the
:meth:`~.Select.correlate` method is preferred, as it provides
standard :term:`method chaining`.
"""
self._auto_correlate = False
self._correlate = set(self._correlate).union(
_interpret_as_from(f) for f in fromclause)
def append_column(self, column):
"""append the given column expression to the columns clause of this
select() construct.
This is an **in-place** mutation method; the
:meth:`~.Select.column` method is preferred, as it provides standard
:term:`method chaining`.
"""
self._reset_exported()
column = _interpret_as_column_or_from(column)
if isinstance(column, ScalarSelect):
column = column.self_group(against=operators.comma_op)
self._raw_columns = self._raw_columns + [column]
def append_prefix(self, clause):
"""append the given columns clause prefix expression to this select()
construct.
This is an **in-place** mutation method; the
:meth:`~.Select.prefix_with` method is preferred, as it provides
standard :term:`method chaining`.
"""
clause = _literal_as_text(clause)
self._prefixes = self._prefixes + (clause,)
def append_whereclause(self, whereclause):
"""append the given expression to this select() construct's WHERE
criterion.
The expression will be joined to existing WHERE criterion via AND.
This is an **in-place** mutation method; the
:meth:`~.Select.where` method is preferred, as it provides standard
:term:`method chaining`.
"""
self._reset_exported()
self._whereclause = and_(
True_._ifnone(self._whereclause), whereclause)
def append_having(self, having):
"""append the given expression to this select() construct's HAVING
criterion.
The expression will be joined to existing HAVING criterion via AND.
This is an **in-place** mutation method; the
:meth:`~.Select.having` method is preferred, as it provides standard
:term:`method chaining`.
"""
self._reset_exported()
self._having = and_(True_._ifnone(self._having), having)
def append_from(self, fromclause):
"""append the given FromClause expression to this select() construct's
FROM clause.
This is an **in-place** mutation method; the
:meth:`~.Select.select_from` method is preferred, as it provides
standard :term:`method chaining`.
"""
self._reset_exported()
fromclause = _interpret_as_from(fromclause)
self._from_obj = self._from_obj.union([fromclause])
@_memoized_property
def _columns_plus_names(self):
if self.use_labels:
names = set()
def name_for_col(c):
if c._label is None or not c._render_label_in_columns_clause:
return (None, c)
name = c._label
if name in names:
name = c.anon_label
else:
names.add(name)
return name, c
return [
name_for_col(c)
for c in util.unique_list(
_select_iterables(self._raw_columns))
]
else:
return [
(None, c)
for c in util.unique_list(
_select_iterables(self._raw_columns))
]
def _populate_column_collection(self):
for name, c in self._columns_plus_names:
if not hasattr(c, '_make_proxy'):
continue
if name is None:
key = None
elif self.use_labels:
key = c._key_label
if key is not None and key in self.c:
key = c.anon_label
else:
key = None
c._make_proxy(self, key=key,
name=name,
name_is_truncatable=True)
def _refresh_for_new_column(self, column):
for fromclause in self._froms:
col = fromclause._refresh_for_new_column(column)
if col is not None:
if col in self.inner_columns and self._cols_populated:
our_label = col._key_label if self.use_labels else col.key
if our_label not in self.c:
return col._make_proxy(
self,
name=col._label if self.use_labels else None,
key=col._key_label if self.use_labels else None,
name_is_truncatable=True)
return None
return None
def _needs_parens_for_grouping(self):
return (
self._limit_clause is not None or
self._offset_clause is not None or
bool(self._order_by_clause.clauses)
)
def self_group(self, against=None):
"""return a 'grouping' construct as per the ClauseElement
specification.
This produces an element that can be embedded in an expression. Note
that this method is called automatically as needed when constructing
expressions and should not require explicit use.
"""
if isinstance(against, CompoundSelect) and \
not self._needs_parens_for_grouping():
return self
return FromGrouping(self)
def union(self, other, **kwargs):
"""return a SQL UNION of this select() construct against the given
selectable."""
return CompoundSelect._create_union(self, other, **kwargs)
def union_all(self, other, **kwargs):
"""return a SQL UNION ALL of this select() construct against the given
selectable.
"""
return CompoundSelect._create_union_all(self, other, **kwargs)
def except_(self, other, **kwargs):
"""return a SQL EXCEPT of this select() construct against the given
selectable."""
return CompoundSelect._create_except(self, other, **kwargs)
def except_all(self, other, **kwargs):
"""return a SQL EXCEPT ALL of this select() construct against the
given selectable.
"""
return CompoundSelect._create_except_all(self, other, **kwargs)
def intersect(self, other, **kwargs):
"""return a SQL INTERSECT of this select() construct against the given
selectable.
"""
return CompoundSelect._create_intersect(self, other, **kwargs)
def intersect_all(self, other, **kwargs):
"""return a SQL INTERSECT ALL of this select() construct against the
given selectable.
"""
return CompoundSelect._create_intersect_all(self, other, **kwargs)
def bind(self):
if self._bind:
return self._bind
froms = self._froms
if not froms:
for c in self._raw_columns:
e = c.bind
if e:
self._bind = e
return e
else:
e = list(froms)[0].bind
if e:
self._bind = e
return e
return None
def _set_bind(self, bind):
self._bind = bind
bind = property(bind, _set_bind)
class ScalarSelect(Generative, Grouping):
_from_objects = []
_is_from_container = True
def __init__(self, element):
self.element = element
self.type = element._scalar_type()
@property
def columns(self):
raise exc.InvalidRequestError('Scalar Select expression has no '
'columns; use this object directly '
'within a column-level expression.')
c = columns
@_generative
def where(self, crit):
"""Apply a WHERE clause to the SELECT statement referred to
by this :class:`.ScalarSelect`.
"""
self.element = self.element.where(crit)
def self_group(self, **kwargs):
return self
class Exists(UnaryExpression):
"""Represent an ``EXISTS`` clause.
"""
__visit_name__ = UnaryExpression.__visit_name__
_from_objects = []
def __init__(self, *args, **kwargs):
"""Construct a new :class:`.Exists` against an existing
:class:`.Select` object.
Calling styles are of the following forms::
# use on an existing select()
s = select([table.c.col1]).where(table.c.col2==5)
s = exists(s)
# construct a select() at once
exists(['*'], **select_arguments).where(criterion)
# columns argument is optional, generates "EXISTS (SELECT *)"
# by default.
exists().where(table.c.col2==5)
"""
if args and isinstance(args[0], (SelectBase, ScalarSelect)):
s = args[0]
else:
if not args:
args = ([literal_column('*')],)
s = Select(*args, **kwargs).as_scalar().self_group()
UnaryExpression.__init__(self, s, operator=operators.exists,
type_=type_api.BOOLEANTYPE,
wraps_column_expression=True)
def select(self, whereclause=None, **params):
return Select([self], whereclause, **params)
def correlate(self, *fromclause):
e = self._clone()
e.element = self.element.correlate(*fromclause).self_group()
return e
def correlate_except(self, *fromclause):
e = self._clone()
e.element = self.element.correlate_except(*fromclause).self_group()
return e
def select_from(self, clause):
"""return a new :class:`.Exists` construct, applying the given
expression to the :meth:`.Select.select_from` method of the select
statement contained.
"""
e = self._clone()
e.element = self.element.select_from(clause).self_group()
return e
def where(self, clause):
"""return a new exists() construct with the given expression added to
its WHERE clause, joined to the existing clause via AND, if any.
"""
e = self._clone()
e.element = self.element.where(clause).self_group()
return e
class TextAsFrom(SelectBase):
"""Wrap a :class:`.TextClause` construct within a :class:`.SelectBase`
interface.
This allows the :class:`.TextClause` object to gain a ``.c`` collection
and other FROM-like capabilities such as :meth:`.FromClause.alias`,
:meth:`.SelectBase.cte`, etc.
The :class:`.TextAsFrom` construct is produced via the
:meth:`.TextClause.columns` method - see that method for details.
.. versionadded:: 0.9.0
.. seealso::
:func:`.text`
:meth:`.TextClause.columns`
"""
__visit_name__ = "text_as_from"
_textual = True
def __init__(self, text, columns, positional=False):
self.element = text
self.column_args = columns
self.positional = positional
@property
def _bind(self):
return self.element._bind
@_generative
def bindparams(self, *binds, **bind_as_values):
self.element = self.element.bindparams(*binds, **bind_as_values)
def _populate_column_collection(self):
for c in self.column_args:
c._make_proxy(self)
def _copy_internals(self, clone=_clone, **kw):
self._reset_exported()
self.element = clone(self.element, **kw)
def _scalar_type(self):
return self.column_args[0].type
class AnnotatedFromClause(Annotated):
def __init__(self, element, values):
# force FromClause to generate their internal
# collections into __dict__
element.c
Annotated.__init__(self, element, values)