添加索引

db/migrate/20200214022547_add_index_to_user_id_and_shixun_id_for_shixuns.rb

@@ -0,0 +1,12 @@
+class AddIndexToUserIdAndShixunIdForShixuns < ActiveRecord::Migration[5.2]
+  def change
+    shixun_members = ShixunMember.select("count(*) cnt, shixun_members.*").group(:user_id, :shixun_id).having("cnt > 1")
+    puts "shixun_members: #{shixun_members.map{|sm| sm.id}}"
+    shixun_members.each do |sm|
+      ShixunModify.find_by(id: sm.id).delete
+    end
+
+    add_index :shixun_members, [:user_id, :shixun_id], unique: true
+
+  end
+end