试卷的答案增加索引

app/controllers/exercise_answers_controller.rb

@@ -4,7 +4,6 @@ class ExerciseAnswersController < ApplicationController
   include ExercisesHelper
 
   def create  #每一次答案的点击，请求一次，实训题不在这里回答
-    ActiveRecord::Base.transaction do
     begin
       q_type = @exercise_question.question_type  #试卷的类型
       choice_id = params[:exercise_choice_id].present? ? params[:exercise_choice_id] : ""
@@ -31,8 +30,8 @@ class ExerciseAnswersController < ApplicationController
 
           ea_ids = ea.pluck(:exercise_choice_id)
           common_answer_ids = choice_ids & ea_ids   #已经存在的试卷选项id
-            new_ids = choice_ids - common_answer_ids   # 新增的id
-            old_ids = ea_ids - common_answer_ids  #没有选择的，则删掉
+          new_ids = (choice_ids - common_answer_ids).uniq   # 新增的id
+          old_ids = (ea_ids - common_answer_ids).uniq  #没有选择的，则删掉
           if new_ids.size > 0
             new_ids.each do |e|
               answer_option = {
@@ -84,7 +83,6 @@ class ExerciseAnswersController < ApplicationController
       raise ActiveRecord::Rollback
     end
   end
-  end
 
   private
 

db/migrate/20191203032557_add_uniq_index_to_exercise_answer.rb

@@ -0,0 +1,17 @@
+class AddUniqIndexToExerciseAnswer < ActiveRecord::Migration[5.2]
+  def change
+    remove_index :exercise_answers, column: [:exercise_question_id, :user_id]
+
+    change_column_default :exercise_answers, :exercise_choice_id, from: nil, to: -1
+    ExerciseAnswer.where(exercise_choice_id: nil).update_all(exercise_choice_id: -1)
+
+    sql = %Q(delete from exercise_answers where (exercise_question_id, user_id, exercise_choice_id) in
+            (select * from (select exercise_question_id, user_id, exercise_choice_id from exercise_answers group by exercise_question_id, user_id, exercise_choice_id having count(*) > 1) a)
+            and id not in (select * from (select min(id) from exercise_answers group by exercise_question_id, user_id, exercise_choice_id having count(*) > 1 order by id) b))
+    ActiveRecord::Base.connection.execute sql
+
+    add_index :exercise_answers, [:exercise_question_id, :user_id, :exercise_choice_id], name: 'exercise_choice_index', unique: true
+
+
+  end
+end