Ticket #13640: 13640_ducktyping.diff

django/db/models/sql/query.py

@@ -14 +14 @@
 from django.db import connections, DEFAULT_DB_ALIAS
 from django.db.models import signals
 from django.db.models.fields import FieldDoesNotExist
+from django.db.models.expressions import ExpressionNode
 from django.db.models.query_utils import select_related_descend, InvalidQuery
 from django.db.models.sql import aggregates as base_aggregates_module
 from django.db.models.sql.constants import *
@@ -1002 +1003 @@
             value = True
         elif callable(value):
             value = value()
-        elif hasattr(value, 'evaluate'):
+        elif hasattr(value, 'prepare') and hasattr(value, 'evaluate')\
+             and callable(value.prepare) and callable(value.evaluate):
             # If value is a query expression, evaluate it
             value = SQLEvaluator(value, self)
             having_clause = value.contains_aggregate

tests/regressiontests/model_regress/tests.py

@@ -1 @@
-from models import Worker
+from models import Worker, Department
 from django.test import TestCase
 
 class RelatedModelOrderedLookupTest(TestCase):
@@ -14 +14 @@
 
     def test_related_lte_lookup(self):
         Worker.objects.filter(department__lte=0)
+
+
+class EvaluateMethodTest(TestCase):
+    """
+    Regression test for #13640: cannot filter by objects with 'evaluate' attr
+    """
+
+    def test_model_with_evaluate_method(self):
+        """
+        Ensures that you can filter by objects that have an 'evaluate' attr
+        """
+        dept = Department.objects.create(pk=1, name='abc')
+        dept.evaluate = 'abc'
+        Worker.objects.filter(department=dept)