son_manipulator.py

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# Copyright 2009-2010 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 bson.dbref import DBRef
from bson.objectid import ObjectId
from bson.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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pymongo
Author(s): Bhaskara Marthi
autogenerated on Fri Jan 11 10:09:03 2013