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mdb-ng/lib/mdb/db.py

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#
# $Id$
#
# This file contains class definitions and interface to the database
# itself while defining objects that the database will return.
#
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import rcs, os
#
# The most generic exception that this library will raise.
#
class PVVDBError(Exception):
pass
#
# PVVMember is the class that represents a record in the database.
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# Its interface is like a dict with a few additional methods to
# talk to the database itself.
#
class PVVMember(dict):
def __init__(self, data, dbref):
# Populate the object with the fields and values provided in the
# `data' object. `dbref' is a pointer to the PVVDB instance that
# created the PVVMember instance.
pass
def save(self):
# Synchronise the object to disk via the database interface.
pass
def load(self):
# Update the object with the data on disk.
pass
def is_saved(self):
# Checks whether the objects need to be saved or loaded.
pass
#
# PVVDB is the class that interfaces to the directory structure and files.
# It also verifies the data read from the files and written to it.
#
class PVVDB:
def __init__(self, base):
# Find the record definition file, read it, verify it and
# set the legal set of fields.
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self.base = base # base database directory
self.locks = [] # list of activated locks
self.rcs = rcs.RCS() # an RCS interface function
def __del__(self):
# clean up locks and such before being deleted.
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for username in self.locks:
self.rcs.unlock(username)
def __filename(self, username):
# transform the username into a tuple with the full name of
# the databasefile and the latest revision number.
return self.rcs.rcsname(os.path.join(self.base, username))
def __format(self, file_path):
# parses and verifies the .format files for a database.
fh = file(file_path)
fmt = {}
for line in fh:
if line[0] == "#":
continue
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name, value = line.strip().split(":", 1)
value = value.split("#", 1)[0].strip()
if not value in ['scalar', 'list']:
raise PVVDBError, "%s not legal .format datatype." % value
fmt[name] = value
return fmt
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def lock(self, username, pedantic=False):
# Lock the record.
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if username in self.locks and pedantic:
raise PVVDBError, "%s already locked." % `username`
self.rcs.lock(self.__filename(username))
self.locks.append(username)
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def unlock(self, username, pedantic=False):
# Unlock the record.
pass
def load(self, username, lock=False):
# Read the record from the database. Will do an automatic lock
# if `lock' is True.
pass
def save(self, username, comment="", lock=False):
# Write the record to the database. Will automatically unlock
# the record if `lock' is True. A `comment' can be supplied that
# explains the changes made.
pass
#
# Regular interface to the database.
#
pathmap = {}
def connect(path):
# returns a PVVDB instance to that path. If asked for another
# PVVDB instance with the same path as earlier, it will return
# the same object.
if not path in pathmap:
pathmap[path] = PVVDB(path)
return pathmap[path]
def disconnect(dbo):
# do not do anything, really. PVVDB objects will clean up
# automatically when deleted. is here for future database
# systems.
pass