Detect usage of a subquery as a constraint value and fail with a Data…

…baseError (other exception may get swallowed and result in an empty set being returned). See issue #8.

djangotoolbox/db/basecompiler.py

@@ -3,6 +3,7 @@
 
 from django.conf import settings
 from django.db.models.fields import NOT_PROVIDED, DecimalField
+from django.db.models.query import QuerySet
 from django.db.models.sql import aggregates as sqlaggregates
 from django.db.models.sql.compiler import SQLCompiler
 from django.db.models.sql.constants import LOOKUP_SEP, MULTI, SINGLE
@@ -211,18 +212,29 @@ def _normalize_lookup_value(self, lookup_type, value, field, annotation):
     def _get_children(self, children):
         """
         Filters out nodes of the given contraint tree not needed for
-        nonrel queries.
+        nonrel queries; checks that given constraints are supported.
         """
         result = []
         for child in children:
 
-            # Remove leafs that were automatically added by
-            # sql.Query.add_filter to handle negations of outer joins.
             if isinstance(child, tuple):
-                constraint = child[0]
-                lookup_type = child[1]
+                constraint, lookup_type, _, value = child
+
+                # When doing a lookup using a QuerySet Django would use
+                # a subquery, but this won't work for nonrel.
+                # TODO: Add a supports_subqueries feature and let
+                #       Django evaluate subqueries instead of passing
+                #       them as SQL strings (QueryWrappers) to
+                #       filtering.
+                if isinstance(value, QuerySet):
+                    raise DatabaseError("Subqueries are not supported (yet).")
+
+                # Remove leafs that were automatically added by
+                # sql.Query.add_filter to handle negations of outer
+                # joins.
                 if lookup_type == 'isnull' and constraint.field is None:
                     continue
+
             result.append(child)
         return result
 

djangotoolbox/tests.py

@@ -1,3 +1,5 @@
+from __future__ import with_statement
+
 from django.core import serializers
 from django.db import models
 from django.db.models import Q
@@ -633,3 +635,28 @@ def test_marked_strings(self):
         self.assertEqual(
             list(String.objects.filter(s__startswith=mark_for_escaping('c'))),
             [c])
+
+
+class FeaturesTest(TestCase):
+    """
+    Some things are unlikely to cause problems for SQL back-ends, but
+    require special handling in nonrel.
+    """
+
+    def test_subqueries(self):
+        """
+        Django includes SQL statements as WHERE tree values when
+        filtering using a QuerySet -- this won't "just work" with
+        nonrel back-ends.
+
+        TODO: Subqueries handling may require a bit of Django
+              changing, but should be easy to support.
+        """
+        target = Target.objects.create(index=1)
+        source = Source.objects.create(index=2, target=target)
+        targets = Target.objects.all()
+        with self.assertRaises(DatabaseError):
+            sources = Source.objects.get(target__in=targets)
+        self.assertEqual(
+            Source.objects.get(target__in=list(targets)),
+            source)