From d1add62a0637b839de8038eba0ea57c77c3e80f1 Mon Sep 17 00:00:00 2001
From: Ross Lawley <ross.lawley@gmail.com>
Date: Wed, 1 Aug 2012 13:11:36 +0100
Subject: [PATCH] More updates

---
 mongoengine/base.py     | 22 ++++++++++++++--------
 mongoengine/queryset.py | 15 ++++++++++-----
 2 files changed, 24 insertions(+), 13 deletions(-)

diff --git a/mongoengine/base.py b/mongoengine/base.py
index 9d342e8c..f8752f36 100644
--- a/mongoengine/base.py
+++ b/mongoengine/base.py
@@ -264,7 +264,7 @@ class ComplexBaseField(BaseField):
     """
 
     field = None
-    _dereference = False
+    __dereference = False
 
     def __get__(self, instance, owner):
         """Descriptor to automatically dereference references.
@@ -276,8 +276,6 @@ class ComplexBaseField(BaseField):
         dereference = self.field is None or isinstance(self.field,
             (GenericReferenceField, ReferenceField))
         if not self._dereference and instance._initialised and dereference:
-            from dereference import DeReference
-            self._dereference = DeReference()  # Cached
             instance._data[self.name] = self._dereference(
                 instance._data.get(self.name), max_depth=1, instance=instance,
                 name=self.name
@@ -293,14 +291,13 @@ class ComplexBaseField(BaseField):
             value = BaseDict(value, instance, self.name)
             instance._data[self.name] = value
 
-        if self._dereference and instance._initialised and \
-            isinstance(value, (BaseList, BaseDict)) and not value._dereferenced:
+        if (instance._initialised and isinstance(value, (BaseList, BaseDict))
+            and not value._dereferenced):
             value = self._dereference(
                 value, max_depth=1, instance=instance, name=self.name
             )
             value._dereferenced = True
             instance._data[self.name] = value
-
         return value
 
     def __set__(self, instance, value):
@@ -441,6 +438,13 @@ class ComplexBaseField(BaseField):
 
     owner_document = property(_get_owner_document, _set_owner_document)
 
+    @property
+    def _dereference(self,):
+        if not self.__dereference:
+            from dereference import DeReference
+            self.__dereference = DeReference()  # Cached
+        return self.__dereference
+
 
 class ObjectIdField(BaseField):
     """An field wrapper around MongoDB's ObjectIds.
@@ -493,8 +497,9 @@ class DocumentMetaclass(type):
                 attrs.update(_get_mixin_fields(p_base))
             return attrs
 
-        metaclass = attrs.get('__metaclass__')
         super_new = super(DocumentMetaclass, cls).__new__
+
+        metaclass = attrs.get('__metaclass__')
         if metaclass and issubclass(metaclass, DocumentMetaclass):
             return super_new(cls, name, bases, attrs)
 
@@ -566,7 +571,8 @@ class DocumentMetaclass(type):
         attrs['_superclasses'] = superclasses
 
         if 'Document' not in _module_registry:
-            from mongoengine import Document, EmbeddedDocument, DictField
+            from mongoengine.document import Document, EmbeddedDocument
+            from mongoengine.fields import DictField
             _module_registry['Document'] = Document
             _module_registry['EmbeddedDocument'] = EmbeddedDocument
             _module_registry['DictField'] = DictField
diff --git a/mongoengine/queryset.py b/mongoengine/queryset.py
index 0d1d95b7..0e93fd2b 100644
--- a/mongoengine/queryset.py
+++ b/mongoengine/queryset.py
@@ -329,6 +329,7 @@ class QuerySet(object):
     """
 
     __already_indexed = set()
+    __dereference = False
 
     def __init__(self, document, collection):
         self._document = document
@@ -600,7 +601,6 @@ class QuerySet(object):
 
             if self._hint != -1:
                 self._cursor_obj.hint(self._hint)
-
         return self._cursor_obj
 
     @classmethod
@@ -1153,8 +1153,7 @@ class QuerySet(object):
         .. versionadded:: 0.4
         .. versionchanged:: 0.5 - Fixed handling references
         """
-        from dereference import DeReference
-        return DeReference()(self._cursor.distinct(field), 1)
+        return self._dereference(self._cursor.distinct(field), 1)
 
     def only(self, *fields):
         """Load only a subset of this document's fields. ::
@@ -1854,10 +1853,16 @@ class QuerySet(object):
 
         .. versionadded:: 0.5
         """
-        from dereference import DeReference
         # Make select related work the same for querysets
         max_depth += 1
-        return DeReference()(self, max_depth=max_depth)
+        return self._dereference(self, max_depth=max_depth)
+
+    @property
+    def _dereference(self):
+        if not self.__dereference:
+            from dereference import DeReference
+            self.__dereference = DeReference()  # Cached
+        return self.__dereference
 
 
 class QuerySetManager(object):