Allow for matches against unsaved objects in querysets (which will therefore

match nothing). This allows for some more straightforward code in the admin
interface.

Fixed #7488 (all the debugging there was done by Brian Rosner, who narrowed it
down to the item in this patch).


git-svn-id: http://code.djangoproject.com/svn/django/trunk@8061 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/db/models/sql/where.py

@@ -35,20 +35,30 @@ class WhereNode(tree.Node):
         storing any reference to field objects). Otherwise, the 'data' is
         stored unchanged and can be anything with an 'as_sql()' method.
         """
+        # Because of circular imports, we need to import this here.
+        from django.db.models.base import ObjectDoesNotExist
+
         if not isinstance(data, (list, tuple)):
             super(WhereNode, self).add(data, connector)
             return
 
         alias, col, field, lookup_type, value = data
+        try:
             if field:
                 params = field.get_db_prep_lookup(lookup_type, value)
                 db_type = field.db_type()
             else:
-            # This is possible when we add a comparison to NULL sometimes (we
+                # This is possible when we add a comparison to NULL sometimes
-            # don't really need to waste time looking up the associated field
+                # (we don't really need to waste time looking up the associated
-            # object).
+                # field object).
                 params = Field().get_db_prep_lookup(lookup_type, value)
                 db_type = None
+        except ObjectDoesNotExist:
+            # This can happen when trying to insert a reference to a null pk.
+            # We break out of the normal path and indicate there's nothing to
+            # match.
+            super(WhereNode, self).add(NothingNode(), connector)
+            return
         if isinstance(value, datetime.datetime):
             annotation = datetime.datetime
         else:
@@ -190,3 +200,14 @@ class EverythingNode(object):
 
     def relabel_aliases(self, change_map, node=None):
         return
+
+class NothingNode(object):
+    """
+    A node that matches nothing.
+    """
+    def as_sql(self, qn=None):
+        raise EmptyResultSet
+
+    def relabel_aliases(self, change_map, node=None):
+        return
+

tests/regressiontests/model_inheritance_regress/models.py

@@ -43,12 +43,17 @@ class ParkingLot(Place):
     def __unicode__(self):
         return u"%s the parking lot" % self.name
 
+class Supplier(models.Model):
+    restaurant = models.ForeignKey(Restaurant)
+
 class Parent(models.Model):
     created = models.DateTimeField(default=datetime.datetime.now)
 
 class Child(Parent):
     name = models.CharField(max_length=10)
 
+
+
 __test__ = {'API_TESTS':"""
 # Regression for #7350, #7202
 # Check that when you create a Parent object with a specific reference to an
@@ -172,4 +177,9 @@ True
 >>> r.id == r.place_ptr_id
 True
 
+# Regression test for #7488. This looks a little crazy, but it's the equivalent
+# of what the admin interface has to do for the edit-inline case.
+>>> Supplier.objects.filter(restaurant=Restaurant(name='xx', address='yy'))
+[]
+
 """}