[soc2009/multidb] Raise an exception at an attempt to do a subquery with 2 different databases. Eventually we'll just evaluate the 2 queries seperates.

git-svn-id: http://code.djangoproject.com/svn/django/branches/soc2009/multidb@11273 bcc190cf-cafb-0310-a4f2-bffc1f526a37

TODO.txt

@@ -14,12 +14,12 @@ that need to be done.  I'm trying to be as granular as possible.
 
     flush, reset, and syncdb need to not prompt the user multiple times.
 
-3)  Handle nesting of Querysets using __in across multiple dbs.
+3)  Handle backends with custom Query classes.
 
-4)  Handle backends with custom Query classes.
+4)  Wait on the merge of the m2m stuff.
 
-5)  Wait on the merge of the m2m stuff.
+5)  Fix django.contrib.gis, it's broken in all sorts of ways.
 
-6)  Fix django.contrib.gis, it's broken in all sorts of ways.
+6)  Generate SQL, instead of an error for nesting on different DBs.
 
 7) Time permitting add support for a ``DatabaseManager``.

django/db/models/fields/__init__.py

@@ -201,9 +201,9 @@ class Field(object):
             if hasattr(value, 'relabel_aliases'):
                 return value
             if hasattr(value, 'as_sql'):
-                sql, params = value.as_sql()
+                sql, params = value.as_sql(connection)
             else:
-                sql, params = value._as_sql()
+                sql, params = value._as_sql(connection)
             return QueryWrapper(('(%s)' % sql), params)
 
 

django/db/models/fields/related.py

@@ -149,9 +149,9 @@ class RelatedField(object):
             if hasattr(value, 'relabel_aliases'):
                 return value
             if hasattr(value, 'as_sql'):
-                sql, params = value.as_sql()
+                sql, params = value.as_sql(connection)
             else:
-                sql, params = value._as_sql()
+                sql, params = value._as_sql(connection)
             return QueryWrapper(('(%s)' % sql), params)
 
         # FIXME: lt and gt are explicitally allowed to make

django/db/models/query.py

@@ -745,12 +745,14 @@ class QuerySet(object):
             self.query.add_fields(field_names, False)
             self.query.set_group_by()
 
-    def _as_sql(self):
+    def _as_sql(self, connection):
         """
         Returns the internal query's SQL and parameters (as a tuple).
         """
         obj = self.values("pk")
-        return obj.query.as_nested_sql()
+        if connection.settings_dict == obj.query.connection.settings_dict:
+            return obj.query.as_nested_sql()
+        raise ValueError("Can't do subqueries with queries on different DBs.")
 
     def _validate(self):
         """
@@ -863,7 +865,7 @@ class ValuesQuerySet(QuerySet):
 
         super(ValuesQuerySet, self)._setup_aggregate_query(aggregates)
 
-    def _as_sql(self):
+    def _as_sql(self, connection):
         """
         For ValueQuerySet (and subclasses like ValuesListQuerySet), they can
         only be used as nested queries if they're already set up to select only
@@ -875,7 +877,11 @@ class ValuesQuerySet(QuerySet):
                 (not self._fields and len(self.model._meta.fields) > 1)):
             raise TypeError('Cannot use a multi-field %s as a filter value.'
                     % self.__class__.__name__)
-        return self._clone().query.as_nested_sql()
+
+        obj = self._clone()
+        if connection.settings_dict == obj.query.connection.settings_dict:
+            return obj.query.as_nested_sql()
+        raise ValueError("Can't do subqueries with queries on different DBs.")
 
     def _validate(self):
         """

tests/regressiontests/multiple_database/tests.py

@@ -93,3 +93,5 @@ if len(settings.DATABASES) > 1:
             a.delete()
             self.assertRaises(Article.DoesNotExist,
                 lambda: Article.objects.get(title="Django Rules!"))
+            self.assertRaises(ValueError,
+                lambda: list(Article.objects.get(pk__in=Article.objects.using('default'))))