Refactor relation merging to create just one relation and then assign values,...

Refactor relation merging to create just one relation and then assign values, instead of creating multiple relation objects.

activerecord/lib/active_record/relation/spawn_methods.rb

@@ -4,30 +4,14 @@ def merge(r)
       merged_relation = clone
       return merged_relation unless r
 
-      merged_relation = merged_relation.eager_load(r.eager_load_values).preload(r.preload_values).includes(r.includes_values)
-
-      merged_relation.readonly_value = r.readonly_value unless r.readonly_value.nil?
-      merged_relation.limit_value = r.limit_value if r.limit_value.present?
-      merged_relation.lock_value = r.lock_value unless merged_relation.lock_value
-      merged_relation.offset_value = r.offset_value if r.offset_value.present?
-
-      merged_relation = merged_relation.
-        joins(r.joins_values).
-        group(r.group_values).
-        select(r.select_values).
-        from(r.from_value).
-        having(r.having_values)
-
-      merged_relation.order_values = r.order_values if r.order_values.present?
-
-      merged_relation.create_with_value = @create_with_value
-
-      if @create_with_value && r.create_with_value
-        merged_relation.create_with_value = @create_with_value.merge(r.create_with_value)
-      else
-        merged_relation.create_with_value = r.create_with_value || @create_with_value
+      (ActiveRecord::Relation::ASSOCIATION_METHODS + ActiveRecord::Relation::MULTI_VALUE_METHODS).reject {|m| [:joins, :where].include?(m)}.each do |method|
+        unless (value = r.send(:"#{method}_values")).blank?
+          merged_relation.send(:"#{method}_values=", value)
+        end
       end
 
+      merged_relation = merged_relation.joins(r.joins_values)
+
       merged_wheres = @where_values
 
       r.where_values.each do |w|
@@ -40,6 +24,14 @@ def merge(r)
 
       merged_relation.where_values = merged_wheres
 
+      ActiveRecord::Relation::SINGLE_VALUE_METHODS.reject {|m| m == :lock}.each do |method|
+        unless (value = r.send(:"#{method}_value")).nil?
+          merged_relation.send(:"#{method}_value=", value)
+        end
+      end
+
+      merged_relation.lock_value = r.lock_value unless merged_relation.lock_value
+
       merged_relation
     end