Added document mixin support

For extendable / reusable documents
Fixes #204

docs/changelog.rst

@@ -5,6 +5,7 @@ Changelog
 Changes in dev
 ==============
 
+- Added Document Mixin support
 - Fixed queryet __repr__ mid iteration
 - Added hint() support, so cantell Mongo the proper index to use for the query
 - Fixed issue with inconsitent setting of _cls breaking inherited referencing

mongoengine/base.py

@@ -389,6 +389,7 @@ class DocumentMetaclass(type):
         class_name = [name]
         superclasses = {}
         simple_class = True
+
         for base in bases:
             # Include all fields present in superclasses
             if hasattr(base, '_fields'):
@@ -397,6 +398,9 @@ class DocumentMetaclass(type):
                 # Get superclasses from superclass
                 superclasses[base._class_name] = base
                 superclasses.update(base._superclasses)
+            else:  # Add any mixin fields
+                attrs.update(dict([(k,v) for k,v in base.__dict__.items()
+                                    if issubclass(v.__class__, BaseField)]))
 
             if hasattr(base, '_meta') and not base._meta.get('abstract'):
                 # Ensure that the Document class may be subclassed -

tests/document.py

@@ -1380,6 +1380,36 @@ class DocumentTest(unittest.TestCase):
         promoted_employee.reload()
         self.assertEqual(promoted_employee.details, None)
 
+    def test_mixins_dont_add_to_types(self):
+
+        class Bob(Document): name = StringField()
+
+        Bob.drop_collection()
+
+        p = Bob(name="Rozza")
+        p.save()
+        Bob.drop_collection()
+
+        class Person(Document, Mixin):
+            pass
+
+        Person.drop_collection()
+
+        p = Person(name="Rozza")
+        p.save()
+        self.assertEquals(p._fields.keys(), ['name', 'id'])
+
+        collection = self.db[Person._meta['collection']]
+        obj = collection.find_one()
+        self.assertEquals(obj['_cls'], 'Person')
+        self.assertEquals(obj['_types'], ['Person'])
+
+
+
+        self.assertEquals(Person.objects.count(), 1)
+        rozza = Person.objects.get(name="Rozza")
+
+        Person.drop_collection()
 
     def test_save_reference(self):
         """Ensure that a document reference field may be saved in the database.

tests/fixtures.py

@@ -18,8 +18,7 @@ class PickleTest(Document):
 
 
 class Mixin(object):
-    number = IntField()
+    name = StringField()
-    string = StringField(choices=(('One', '1'), ('Two', '2')))
 
 
 class Base(Document):