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# Copyright 2009 10gen, Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""Manipulators that can edit SON objects as they enter and exit a database.
New manipulators should be defined as subclasses of SONManipulator and can be
installed on a database by calling
`pymongo.database.Database.add_son_manipulator`."""
from objectid import ObjectId
from dbref import DBRef
from son import SON
class SONManipulator(object):
"""A base son manipulator.
This manipulator just saves and restores objects without changing them.
"""
def will_copy(self):
"""Will this SON manipulator make a copy of the incoming document?
Derived classes that do need to make a copy should override this
method, returning True instead of False. All non-copying manipulators
will be applied first (so that the user's document will be updated
appropriately), followed by copying manipulators.
"""
return False
def transform_incoming(self, son, collection):
"""Manipulate an incoming SON object.
:Parameters:
- `son`: the SON object to be inserted into the database
- `collection`: the collection the object is being inserted into
"""
if self.will_copy():
return SON(son)
return son
def transform_outgoing(self, son, collection):
"""Manipulate an outgoing SON object.
:Parameters:
- `son`: the SON object being retrieved from the database
- `collection`: the collection this object was stored in
"""
if self.will_copy():
return SON(son)
return son
class ObjectIdInjector(SONManipulator):
"""A son manipulator that adds the _id field if it is missing.
"""
def transform_incoming(self, son, collection):
"""Add an _id field if it is missing.
"""
if not "_id" in son:
son["_id"] = ObjectId()
return son
# This is now handled during BSON encoding (for performance reasons),
# but I'm keeping this here as a reference for those implementing new
# SONManipulators.
class ObjectIdShuffler(SONManipulator):
"""A son manipulator that moves _id to the first position.
"""
def will_copy(self):
"""We need to copy to be sure that we are dealing with SON, not a dict.
"""
return True
def transform_incoming(self, son, collection):
"""Move _id to the front if it's there.
"""
if not "_id" in son:
return son
transformed = SON({"_id": son["_id"]})
transformed.update(son)
return transformed
class NamespaceInjector(SONManipulator):
"""A son manipulator that adds the _ns field.
"""
def transform_incoming(self, son, collection):
"""Add the _ns field to the incoming object
"""
son["_ns"] = collection.name
return son
class AutoReference(SONManipulator):
"""Transparently reference and de-reference already saved embedded objects.
This manipulator should probably only be used when the NamespaceInjector is
also being used, otherwise it doesn't make too much sense - documents can
only be auto-referenced if they have an *_ns* field.
NOTE: this will behave poorly if you have a circular reference.
TODO: this only works for documents that are in the same database. To fix
this we'll need to add a DatabaseInjector that adds *_db* and then make
use of the optional *database* support for DBRefs.
"""
def __init__(self, db):
self.__database = db
def will_copy(self):
"""We need to copy so the user's document doesn't get transformed refs.
"""
return True
def transform_incoming(self, son, collection):
"""Replace embedded documents with DBRefs.
"""
def transform_value(value):
if isinstance(value, dict):
if "_id" in value and "_ns" in value:
return DBRef(value["_ns"], transform_value(value["_id"]))
else:
return transform_dict(SON(value))
elif isinstance(value, list):
return [transform_value(v) for v in value]
return value
def transform_dict(object):
for (key, value) in object.items():
object[key] = transform_value(value)
return object
return transform_dict(SON(son))
def transform_outgoing(self, son, collection):
"""Replace DBRefs with embedded documents.
"""
def transform_value(value):
if isinstance(value, DBRef):
return self.__database.dereference(value)
elif isinstance(value, list):
return [transform_value(v) for v in value]
elif isinstance(value, dict):
return transform_dict(SON(value))
return value
def transform_dict(object):
for (key, value) in object.items():
object[key] = transform_value(value)
return object
return transform_dict(SON(son))
# TODO make a generic translator for custom types. Take encode, decode,
# should_encode and should_decode functions and just encode and decode where
# necessary. See examples/custom_type.py for where this would be useful.
# Alternatively it could take a should_encode, to_binary, from_binary and
# binary subtype.
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