added default ordering to meta options, included docs and tests

docs/userguide.rst

@@ -183,6 +183,41 @@ sign. Note that direction only matters on multi-field indexes. ::
         meta = {
             'indexes': ['title', ('title', '-rating')]
         }
+        
+Ordering
+--------
+
+A default ordering can be specified for your :class:`~mongoengine.queryset.QuerySet`
+using the :attr:`ordering` attributeof :attr:`~Document.meta`. 
+Ordering will be applied when the ``QuerySet`` is created, and can be 
+overridden by subsequent calls to :meth:`~mongoengine.QuerySet.order_by`. ::
+
+    from datetime import datetime
+
+    class BlogPost(Document):
+        title = StringField()
+        published_date = DateTimeField()
+
+        meta = {
+            'ordering': ['-published_date']
+        }
+
+    blog_post_1 = BlogPost(title="Blog Post #1", published_date=datetime(2010, 1, 5, 0, 0 ,0))
+    blog_post_2 = BlogPost(title="Blog Post #2", published_date=datetime(2010, 1, 6, 0, 0 ,0))
+    blog_post_3 = BlogPost(title="Blog Post #3", published_date=datetime(2010, 1, 7, 0, 0 ,0))
+
+    blog_post_1.save()
+    blog_post_2.save()
+    blog_post_3.save()
+
+    # get the "first" BlogPost using default ordering
+    # from BlogPost.meta.ordering
+    latest_post = BlogPost.objects.first() 
+    self.assertEqual(latest_post.title, "Blog Post #3")
+
+    # override default ordering, order BlogPosts by "published_date"
+    first_post = BlogPost.objects.order_by("+published_date").first()
+    self.assertEqual(first_post.title, "Blog Post #1")
 
 Document inheritance
 --------------------

mongoengine/base.py

@@ -155,6 +155,7 @@ class TopLevelDocumentMetaclass(DocumentMetaclass):
             'allow_inheritance': True,
             'max_documents': None,
             'max_size': None,
+            'ordering': [], # default ordering applied at runtime
             'indexes': [] # indexes to be ensured at runtime
         }
 

mongoengine/queryset.py

@@ -59,7 +59,6 @@ class QuerySet(object):
         # ensure document-defined indexes are created
         if self._document._meta['indexes']:
             for key_or_list in self._document._meta['indexes']:
-                # print "key", key_or_list
                 self.ensure_index(key_or_list)
         
         query = QuerySet._transform_query(_doc_cls=self._document, **query)
@@ -70,6 +69,11 @@ class QuerySet(object):
     def _cursor(self):
         if not self._cursor_obj:
             self._cursor_obj = self._collection.find(self._query)
+            
+            # apply default ordering
+            if self._document._meta['ordering']:
+                self.order_by(*self._document._meta['ordering'])
+            
         return self._cursor_obj
 
     @classmethod

tests/queryset.py

@@ -131,6 +131,36 @@ class QuerySetTest(unittest.TestCase):
         person = self.Person.objects.with_id(person1.id)
         self.assertEqual(person.name, "User A")
 
+    def test_ordering(self):
+        """Ensure default ordering is applied and can be overridden.
+        """
+        from datetime import datetime
+
+        class BlogPost(Document):
+            title = StringField()
+            published_date = DateTimeField()
+
+            meta = {
+                'ordering': ['-published_date']
+            }
+
+        blog_post_1 = BlogPost(title="Blog Post #1", published_date=datetime(2010, 1, 5, 0, 0 ,0))
+        blog_post_2 = BlogPost(title="Blog Post #2", published_date=datetime(2010, 1, 6, 0, 0 ,0))
+        blog_post_3 = BlogPost(title="Blog Post #3", published_date=datetime(2010, 1, 7, 0, 0 ,0))
+
+        blog_post_1.save()
+        blog_post_2.save()
+        blog_post_3.save()
+        
+        # get the "first" BlogPost using default ordering
+        # from BlogPost.meta.ordering
+        latest_post = BlogPost.objects.first() 
+        self.assertEqual(latest_post.title, "Blog Post #3")
+        
+        # override default ordering, order BlogPosts by "published_date"
+        first_post = BlogPost.objects.order_by("+published_date").first()
+        self.assertEqual(first_post.title, "Blog Post #1")
+
     def test_find_embedded(self):
         """Ensure that an embedded document is properly returned from a query.
         """