Ticket #9961: 9961_r17068.diff

django/db/models/query.py

@@ -657 +657 @@
         If fields are specified, they must be ForeignKey fields and only those
         related objects are included in the selection.
         """
-        depth = kwargs.pop('depth', 0)
+        depth = kwargs.pop('depth', None)
         if kwargs:
             raise TypeError('Unexpected keyword arguments to select_related: %s'
                     % (kwargs.keys(),))
@@ -668 +668 @@
             obj.query.add_select_related(fields)
         else:
             obj.query.select_related = True
-        if depth:
+        if depth is not None:
             obj.query.max_depth = depth
         return obj
 
@@ -1217 +1217 @@
     # situations).
     value_annotation = False
 
-def get_klass_info(klass, max_depth=0, cur_depth=0, requested=None,
+def get_klass_info(klass, max_depth=None, cur_depth=0, requested=None,
                    only_load=None, local_only=False):
     """
     Helper function that recursively returns an information for a klass, to be
@@ -1241 +1241 @@
      * local_only - Only populate local fields. This is used when
        following reverse select-related relations
     """
-    if max_depth and requested is None and cur_depth > max_depth:
+    if max_depth is not None and requested is None and cur_depth > max_depth:
         # We've recursed deeply enough; stop now.
         return None
 

django/db/models/sql/compiler.py

@@ -517 +517 @@
         (for example, cur_depth=1 means we are looking at models with direct
         connections to the root model).
         """
-        if not restricted and self.query.max_depth and cur_depth > self.query.max_depth:
+        if not restricted and self.query.max_depth is not None and cur_depth > self.query.max_depth:
             # We've recursed far enough; bail out.
             return
 

docs/ref/models/querysets.txt

@@ -642 +642 @@
     p = b.author         # Doesn't hit the database.
     c = p.hometown       # Requires a database call.
 
+You can also use the ``depth`` argument to cancel an existing 
+``select_related()`` on the query by setting ``depth`` to "0". For example 
+these three queries are equivalent::
+
+    b = Book.objects.get(id=4)
+    b = Book.objects.select_related(depth=0).get(id=4)
+    b = Book.objects.select_related('author').select_related(depth=0).get(id=4)
+
 Sometimes you only want to access specific models that are related to your root
 model, not all of the related models. In these cases, you can pass the related
 field names to ``select_related()`` and it will only follow those relations.

tests/modeltests/select_related/tests.py

@@ -160 +160 @@
             Species.objects.select_related,
             'genus__family__order', depth=4
         )
+
+    def test_depth_zero(self):
+        with self.assertNumQueries(9):
+            world = Species.objects.all().select_related(depth=0)
+            families = [o.genus.family.name for o in world]
+            self.assertEqual(sorted(families), [
+                'Amanitacae',
+                'Drosophilidae',
+                'Fabaceae',
+                'Hominidae',
+            ])
+
+    def test_reset_depth(self):
+        with self.assertNumQueries(9):
+            world = Species.objects.all().select_related('genus').select_related(depth=0)
+            families = [o.genus.family.name for o in world]
+            self.assertEqual(sorted(families), [
+                'Amanitacae',
+                'Drosophilidae',
+                'Fabaceae',
+                'Hominidae',
+            ])
+