Issue #25: __model_cls__ attribute validation within metaclass

Author: boonya

domain_models/views.py

@@ -1,7 +1,25 @@
 """Contextual view module."""
 from domain_models import models
+import six
 
 
+class ContextViewMetaClass(type):
+    """Context view meta class."""
+
+    def __new__(mcs, class_name, bases, attributes):
+        """Context view class factory."""
+        if bases[0] is not object:
+            __model_cls__ = attributes.get('__model_cls__')
+            if __model_cls__ is None:
+                raise AttributeError("Attribute __model_cls__ is required.")
+            if not issubclass(__model_cls__, models.DomainModel):
+                raise TypeError("Attribute __model_cls__ must be subclass of "
+                                "DomainModel.")
+
+        return type.__new__(mcs, class_name, bases, attributes)
+
+
+@six.add_metaclass(ContextViewMetaClass)
 class ContextView(object):
     """Contextual view class."""
 
@@ -12,10 +30,6 @@ def __init__(self, model):
 
         :param model: DomainModel
         """
-        if not issubclass(self.__model_cls__, models.DomainModel):
-            raise TypeError("Attribute __model__ must be subclass of "
-                            "DomainModel")
-
         if not isinstance(model, self.__model_cls__):
             raise TypeError("\"{0}\" is not an instance of {1}".format(
                 model, self.__model_cls__))

tests/test_context_view.py

@@ -111,26 +111,6 @@ def get_data(self):
         }
 
 
-class ModelUndefinedContext(views.ContextView):
-    """Model undefined"""
-
-    def get_data(self):
-        pass
-
-
-class WrongModelContext(views.ContextView):
-    """Wrong model defined."""
-    __model_cls__ = type
-
-    def get_data(self):
-        pass
-
-
-class GetterUndefinedContext(views.ContextView):
-    """Getter undefined."""
-    __model_cls__ = Profile
-
-
 class TestContextView(unittest.TestCase):
     main_photo = Photo(id=1, title='main photo', path='path/to/the/main/photo',
                        public=True)
@@ -151,14 +131,19 @@ def test_wrong_model_passed(self):
             PublicProfile("invalid argument")
 
     def test_model_undefined(self):
-        with self.assertRaises(TypeError):
-            ModelUndefinedContext("it doesn't matter")
+        with self.assertRaises(AttributeError):
+            class ModelUndefinedContext(views.ContextView):
+                pass
 
     def test_wrong_model_defined(self):
         with self.assertRaises(TypeError):
-            WrongModelContext("it doesn't matter")
+            class WrongModelContext(views.ContextView):
+                __model_cls__ = type
 
     def test_getter_undefined(self):
+        class GetterUndefinedContext(views.ContextView):
+            __model_cls__ = Profile
+
         contextual_view = GetterUndefinedContext(self.profile)
         with self.assertRaises(NotImplementedError):
             contextual_view.get_data()