Use linkage: always: true on belongs_to relationships to always include the type and id on the relationship hash

Author: jkeen

lib/graphiti/util/serializer_relationships.rb

@@ -49,10 +49,13 @@ def block
         data_proc_ref = data_proc
         self_ref = self
         validate_link! if eagerly_validate_links?
-
         proc do
           data { instance_eval(&data_proc_ref) }
 
+          # include relationship links for belongs_to relationships
+          # https://github.com/graphiti-api/graphiti/issues/167
+          linkage always: true if sideload_ref.type == :belongs_to
+
           if link_ref
             if @proxy.query.links?
               self_ref.send(:validate_link!) unless self_ref.send(:eagerly_validate_links?)