Raise exception for models defining discriminator value, but no column

cassandra/cqlengine/models.py

@@ -796,6 +796,9 @@ class ModelMetaClass(type):
         if len(discriminator_columns) > 1:
             raise ModelDefinitionException('only one discriminator_column (polymorphic_key (deprecated)) can be defined in a model, {} found'.format(len(discriminator_columns)))
 
+        if attrs['__discriminator_value__'] and not is_polymorphic:
+            raise ModelDefinitionException('__discriminator_value__ specified, but no base columns defined with discriminator_column=True')
+
         discriminator_column_name, discriminator_column = discriminator_columns[0] if discriminator_columns else (None, None)
 
         if isinstance(discriminator_column, (columns.BaseContainerColumn, columns.Counter)):

tests/integration/cqlengine/model/test_polymorphism.py

@@ -33,6 +33,11 @@ class TestPolymorphicClassConstruction(BaseCassEngTestCase):
                 type1 = columns.Integer(polymorphic_key=True)
                 type2 = columns.Integer(polymorphic_key=True)
 
+    def test_no_polymorphic_key_column_failure(self):
+        with self.assertRaises(models.ModelDefinitionException):
+            class M(models.Model):
+                __polymorphic_key__ = 1
+
     def test_polymorphic_key_inheritance(self):
         """ Tests that polymorphic_key attribute is not inherited """
         class Base(models.Model):
@@ -264,6 +269,11 @@ class TestInheritanceClassConstruction(BaseCassEngTestCase):
                 type1 = columns.Integer(discriminator_column=True)
                 type2 = columns.Integer(discriminator_column=True)
 
+    def test_no_discriminator_column_failure(self):
+        with self.assertRaises(models.ModelDefinitionException):
+            class M(models.Model):
+                __discriminator_value__ = 1
+
     def test_discriminator_value_inheritance(self):
         """ Tests that discriminator_column attribute is not inherited """
         class Base(models.Model):