选用实践课程的搜索

app/controllers/subjects_controller.rb

@@ -69,7 +69,8 @@ class SubjectsController < ApplicationController
     else
       @subjects = @subjects[offset, limit]
       subject_ids = @subjects.pluck(:id)
-      @subjects = Subject.where(id: subject_ids).order("field(id,#{subject_ids.join(',')})").includes(:shixuns, :repertoire)
+      order_ids = subject_ids.size > 0 ? subject_ids.join(',') : -1
+      @subjects = Subject.where(id: subject_ids).order("field(id,#{order_ids})").includes(:shixuns, :repertoire)
     end
   end