allow unions to be used in connections

graphene/relay/connection.py

@@ -12,6 +12,7 @@ from ..types import (AbstractType, Boolean, Enum, Int, Interface, List, NonNull,
 from ..types.field import Field
 from ..types.objecttype import ObjectType, ObjectTypeMeta
 from ..types.options import Options
+from ..types import Union
 from ..utils.is_base_type import is_base_type
 from ..utils.props import props
 from .node import is_node
@@ -109,7 +110,7 @@ class IterableConnectionField(Field):
     @property
     def type(self):
         type = super(IterableConnectionField, self).type
-        if is_node(type):
+        if issubclass(type, Union) or is_node(type):
             connection_type = type.Connection
         else:
             connection_type = type

graphene/types/union.py

@@ -24,7 +24,21 @@ class UnionMeta(type):
             len(options.types) > 0
         ), 'Must provide types for Union {}.'.format(options.name)
 
-        return type.__new__(cls, name, bases, dict(attrs, _meta=options))
+        cls = type.__new__(cls, name, bases, dict(attrs, _meta=options))
+
+        get_connection = getattr(cls, 'get_connection', None)
+        if not get_connection:
+            from graphene.relay.connection import Connection
+
+            class DefaultUnionConnection(Connection):
+                class Meta:
+                    node = cls
+
+            cls.Connection = DefaultUnionConnection
+        else:
+            cls.Connection = get_connection()
+
+        return cls
 
     def __str__(cls):  # noqa: N805
         return cls._meta.name