Added ability to create topic sorts in plugins with custom_fields

lib/topic_query.rb

@@ -401,6 +401,11 @@ class TopicQuery
         return result.includes(:first_post).order("(SELECT like_count FROM posts p3 WHERE p3.topic_id = topics.id AND p3.post_number = 1) #{sort_dir}")
       end
 
+      if sort_column.start_with?('custom_fields')
+        field = sort_column.split('.')[1]
+        return result.order("(SELECT CASE WHEN EXISTS (SELECT true FROM topic_custom_fields tcf WHERE tcf.topic_id::integer = topics.id::integer AND tcf.name = '#{field}') THEN (SELECT value::integer FROM topic_custom_fields tcf WHERE tcf.topic_id::integer = topics.id::integer AND tcf.name = '#{field}') ELSE 0 END) #{sort_dir}")
+      end
+
       result.order("topics.#{sort_column} #{sort_dir}")
     end
 

spec/components/topic_query_spec.rb

@@ -232,6 +232,33 @@ describe TopicQuery do
 
           # returns the topics in reverse posters order if requested" do
           expect(ids_in_order('posters', false)).to eq([archived_topic, closed_topic, invisible_topic, future_topic, regular_topic, pinned_topic].map(&:id))
+    
+          # sets a custom field for each topic to emulate a plugin
+          regular_topic.custom_fields["sheep"] = 26
+          pinned_topic.custom_fields["sheep"] = 47
+          archived_topic.custom_fields["sheep"] = 69
+          invisible_topic.custom_fields["sheep"] = 12
+          closed_topic.custom_fields["sheep"] = 31
+          future_topic.custom_fields["sheep"] = 53
+          
+          regular_topic.save
+          pinned_topic.save
+          archived_topic.save
+          invisible_topic.save
+          closed_topic.save
+          future_topic.save
+
+          # adds the custom field as a viable sort option
+          class ::TopicQuery
+            SORTABLE_MAPPING["sheep"] = "custom_fields.sheep"
+          end
+          # returns the topics in the sheep order if requested" do
+          expect(ids_in_order('sheep')).to eq([archived_topic, future_topic, pinned_topic, closed_topic, regular_topic, invisible_topic].map(&:id))
+
+          # returns the topics in reverse sheep order if requested" do
+          expect(ids_in_order('sheep', false)).to eq([invisible_topic, regular_topic, closed_topic, pinned_topic, future_topic, archived_topic].map(&:id))
+    
+
         end
 
       end