Use subqueries to find nested members more efficiently

app/controllers/api/nodes/ways_controller.rb

@@ -10,9 +10,11 @@ module Api
       # :node_id parameter. note that this used to return deleted ways as well, but
       # this seemed not to be the expected behaviour, so it was removed.
       def index
-        way_ids = WayNode.where(:node_id => params[:node_id]).collect { |ws| ws.id[0] }.uniq
-
-        @ways = Way.where(:id => way_ids, :visible => true)
+        @ways = Way
+                .visible
+                .where(:id => WayNode.where(
+                  :node_id => params[:node_id]
+                ).select(:way_id))
 
         # Render the result
         respond_to do |format|