Use underscore instead of downcase (#1366)

Use underscore instead of downcase for polymorphic names

Author: lgebhardt

lib/jsonapi/active_relation_resource.rb

@@ -649,7 +649,7 @@ def find_related_polymorphic_fragments(source_rids, relationship, options, conne
               end
             end
 
-            relation_position = relation_positions[row[2].downcase.pluralize]
+            relation_position = relation_positions[row[2].underscore.pluralize]
             model_fields = relation_position[:model_fields]
             cache_field = relation_position[:cache_field]
             cache_offset = relation_position[:cache_offset]

lib/jsonapi/basic_resource.rb

@@ -873,7 +873,7 @@ def _polymorphic_name
         if !_polymorphic
           ''
         else
-          @_polymorphic_name ||= _model_name.to_s.downcase
+          @_polymorphic_name ||= _model_name.to_s.underscore
         end
       end
 
@@ -927,7 +927,7 @@ def _polymorphic_types
             next unless Module === klass
             if klass < ActiveRecord::Base
               klass.reflect_on_all_associations(:has_many).select{|r| r.options[:as] }.each do |reflection|
-                (hash[reflection.options[:as]] ||= []) << klass.name.downcase
+                (hash[reflection.options[:as]] ||= []) << klass.name.underscore
               end
             end
           end

lib/jsonapi/relationship.rb

@@ -63,7 +63,7 @@ def self.polymorphic_types(name)
           next unless Module === klass
           if ActiveRecord::Base > klass
             klass.reflect_on_all_associations(:has_many).select{|r| r.options[:as] }.each do |reflection|
-              (hash[reflection.options[:as]] ||= []) << klass.name.downcase
+              (hash[reflection.options[:as]] ||= []) << klass.name.underscore
             end
           end
         end