Added no_dereference method for querysets (#82) (#61)

docs/changelog.rst

@@ -39,6 +39,7 @@ Changes in 0.8.X
 - Added switch_collection method to document instances (#220)
 - Added support for compound primary keys (#149) (#121)
 - Fixed overriding objects with custom manager (#58)
+- Added no_dereference method for querysets (#82) (#61)
 
 Changes in 0.7.9
 ================

docs/guide/querying.rst

@@ -373,17 +373,22 @@ Turning off dereferencing
 -------------------------
 
 Sometimes for performance reasons you don't want to automatically dereference
-data .  To turn off all dereferencing you can use the
+data. To turn off dereferencing of the results of a query use
+:func:`~mongoengine.queryset.QuerySet.no_dereference` on the queryset like so::
+
+    post = Post.objects.no_dereference().first()
+    assert(isinstance(post.author, ObjectId))
+
+You can also turn off all dereferencing for a fixed period by using the
 :class:`~mongoengine.context_managers.no_dereference` context manager::
 
     with no_dereference(Post) as Post:
         post = Post.objects.first()
         assert(isinstance(post.author, ObjectId))
 
-.. note::
+    # Outside the context manager dereferencing occurs.
+    assert(isinstance(post.author, User))
 
-    :class:`~mongoengine.context_managers.no_dereference` only works on the
-    Default QuerySet manager.
 
 Advanced queries
 ================

mongoengine/base/document.py

@@ -1,3 +1,4 @@
+import copy
 import operator
 from functools import partial
 
@@ -461,9 +462,10 @@ class BaseDocument(object):
         return cls._meta.get('collection', None)
 
     @classmethod
-    def _from_son(cls, son):
+    def _from_son(cls, son, _auto_dereference=True):
         """Create an instance of a Document (subclass) from a PyMongo SON.
         """
+
         # get the class name from the document, falling back to the given
         # class if unavailable
         class_name = son.get('_cls', cls._class_name)
@@ -480,7 +482,12 @@ class BaseDocument(object):
         changed_fields = []
         errors_dict = {}
 
-        for field_name, field in cls._fields.iteritems():
+        fields = cls._fields
+        if not _auto_dereference:
+            fields = copy.copy(fields)
+
+        for field_name, field in fields.iteritems():
+            field._auto_dereference = _auto_dereference
             if field.db_field in data:
                 value = data[field.db_field]
                 try:
@@ -507,6 +514,8 @@ class BaseDocument(object):
         obj = cls(__auto_convert=False, **data)
         obj._changed_fields = changed_fields
         obj._created = False
+        if not _auto_dereference:
+            obj._fields = fields
         return obj
 
     @classmethod

mongoengine/base/fields.py

@@ -168,6 +168,7 @@ class ComplexBaseField(BaseField):
                        (self.field is None or isinstance(self.field,
                         (GenericReferenceField, ReferenceField))))
 
+        self._auto_dereference = instance._fields[self.name]._auto_dereference
         if not self.__dereference and instance._initialised and dereference:
             instance._data[self.name] = self._dereference(
                 instance._data.get(self.name), max_depth=1, instance=instance,

mongoengine/context_managers.py

@@ -93,7 +93,8 @@ class switch_collection(object):
 class no_dereference(object):
     """ no_dereference context manager.
 
-    Turns off all dereferencing in Documents::
+    Turns off all dereferencing in Documents for the duration of the context
+    manager::
 
         with no_dereference(Group) as Group:
             Group.objects.find()
@@ -118,21 +119,12 @@ class no_dereference(object):
 
     def __enter__(self):
         """ change the objects default and _auto_dereference values"""
-        if 'queryset_class' in self.cls._meta:
-            raise OperationError("no_dereference context manager only works on"
-                                 " default queryset classes")
-        objects = self.cls.__dict__['objects']
-        objects.default = QuerySetNoDeRef
-        self.cls.objects = objects
         for field in self.deref_fields:
             self.cls._fields[field]._auto_dereference = False
         return self.cls
 
     def __exit__(self, t, value, traceback):
         """ Reset the default and _auto_dereference values"""
-        objects = self.cls.__dict__['objects']
-        objects.default = QuerySet
-        self.cls.objects = objects
         for field in self.deref_fields:
             self.cls._fields[field]._auto_dereference = True
         return self.cls
@@ -145,7 +137,7 @@ class QuerySetNoDeRef(QuerySet):
 
 
 class query_counter(object):
-    """ Query_counter contextmanager to get the number of queries. """
+    """ Query_counter context manager to get the number of queries. """
 
     def __init__(self):
         """ Construct the query_counter. """

mongoengine/fields.py

@@ -777,7 +777,7 @@ class ReferenceField(BaseField):
 
         # Get value from document instance if available
         value = instance._data.get(self.name)
-
+        self._auto_dereference = instance._fields[self.name]._auto_dereference
         # Dereference DBRefs
         if self._auto_dereference and isinstance(value, DBRef):
             value = self.document_type._get_db().dereference(value)
@@ -859,7 +859,8 @@ class GenericReferenceField(BaseField):
             return self
 
         value = instance._data.get(self.name)
-        if isinstance(value, (dict, SON)):
+        self._auto_dereference = instance._fields[self.name]._auto_dereference
+        if self._auto_dereference and isinstance(value, (dict, SON)):
             instance._data[self.name] = self.dereference(value)
 
         return super(GenericReferenceField, self).__get__(instance, owner)

mongoengine/queryset/queryset.py

@@ -42,6 +42,7 @@ class QuerySet(object):
     providing :class:`~mongoengine.Document` objects as the results.
     """
     __dereference = False
+    _auto_dereference = True
 
     def __init__(self, document, collection):
         self._document = document
@@ -145,10 +146,12 @@ class QuerySet(object):
         elif isinstance(key, int):
             if queryset._scalar:
                 return queryset._get_scalar(
-                        queryset._document._from_son(queryset._cursor[key]))
+                        queryset._document._from_son(queryset._cursor[key],
+                            _auto_dereference=self._auto_dereference))
             if queryset._as_pymongo:
                 return queryset._get_as_pymongo(queryset._cursor.next())
-            return queryset._document._from_son(queryset._cursor[key])
+            return queryset._document._from_son(queryset._cursor[key],
+                            _auto_dereference=self._auto_dereference)
         raise AttributeError
 
     def __repr__(self):
@@ -515,7 +518,7 @@ class QuerySet(object):
             '_where_clause', '_loaded_fields', '_ordering', '_snapshot',
             '_timeout', '_class_check', '_slave_okay', '_read_preference',
             '_iter', '_scalar', '_as_pymongo', '_as_pymongo_coerce',
-            '_limit', '_skip', '_hint')
+            '_limit', '_skip', '_hint', '_auto_dereference')
 
         for prop in copy_props:
             val = getattr(self, prop)
@@ -1135,6 +1138,12 @@ class QuerySet(object):
             self.__dereference = _import_class('DeReference')()
         return self.__dereference
 
+    def no_dereference(self):
+        """Turn off any dereferencing."""
+        queryset = self.clone()
+        queryset._auto_dereference = False
+        return queryset
+
     # Helper Functions
 
     def _item_frequencies_map_reduce(self, field, normalize=False):

tests/queryset/queryset.py

@@ -3103,5 +3103,26 @@ class QuerySetTest(unittest.TestCase):
         self.assertEqual(results[1]['name'], 'Barack Obama')
         self.assertEqual(results[1]['price'], Decimal('2.22'))
 
+    def test_no_dereference(self):
+
+        class Organization(Document):
+            name = StringField()
+
+        class User(Document):
+            name = StringField()
+            organization = ReferenceField(Organization)
+
+        User.drop_collection()
+        Organization.drop_collection()
+
+        whitehouse = Organization(name="White House").save()
+        User(name="Bob Dole", organization=whitehouse).save()
+
+        qs = User.objects()
+        self.assertTrue(isinstance(qs.first().organization, Organization))
+        self.assertFalse(isinstance(qs.no_dereference().first().organization,
+                                    Organization))
+        self.assertTrue(isinstance(qs.first().organization, Organization))
+
 if __name__ == '__main__':
     unittest.main()