Improved ConnectionField exception message. Fixed #356

graphene/relay/connection.py

@@ -115,7 +115,7 @@ class IterableConnectionField(Field):
             connection_type = type
         assert issubclass(connection_type, Connection), (
             '{} type have to be a subclass of Connection. Received "{}".'
-        ).format(str(self), connection_type)
+        ).format(self.__class__.__name__, connection_type)
         return connection_type
 
     @classmethod

graphene/relay/node.py

@@ -12,9 +12,9 @@ def is_node(objecttype):
     '''
     Check if the given objecttype has Node as an interface
     '''
-    assert issubclass(objecttype, ObjectType), (
-        'Only ObjectTypes can have a Node interface. Received %s'
-    ) % objecttype
+    if not issubclass(objecttype, ObjectType):
+        return False
+
     for i in objecttype._meta.interfaces:
         if issubclass(i, Node):
             return True

graphene/tests/issues/test_356.py

@@ -0,0 +1,24 @@
+# https://github.com/graphql-python/graphene/issues/356
+
+import pytest
+import graphene
+from graphene import relay
+
+class SomeTypeOne(graphene.ObjectType):
+    pass
+
+class SomeTypeTwo(graphene.ObjectType):
+    pass
+
+class MyUnion(graphene.Union):
+    class Meta:
+        types = (SomeTypeOne, SomeTypeTwo)
+
+def test_issue():
+    with pytest.raises(Exception) as exc_info:
+        class Query(graphene.ObjectType):
+            things = relay.ConnectionField(MyUnion)
+
+        schema = graphene.Schema(query=Query)
+
+    assert str(exc_info.value) == 'IterableConnectionField type have to be a subclass of Connection. Received "MyUnion".'