diff --git a/app/models/exercise.rb b/app/models/exercise.rb
index af84a5c49..60409e51d 100644
--- a/app/models/exercise.rb
+++ b/app/models/exercise.rb
@@ -3,11 +3,11 @@ class Exercise < ApplicationRecord
   belongs_to :exercise_bank, optional: true
   belongs_to :user
 
-  has_many :exercise_users
-  has_many :exercise_questions
-  has_many :exercise_group_settings
+  has_many :exercise_users, :dependent => :delete_all
+  has_many :exercise_questions, :dependent => :delete_all
+  has_many :exercise_group_settings, :dependent => :delete_all
   has_many :tidings, as: :container
-  has_many :course_acts, class_name: 'CourseActivity', as: :course_act, dependent: :destroy
+  has_many :course_acts, class_name: 'CourseActivity', as: :course_act, :dependent => :delete_all
 
   scope :is_exercise_published, -> { where("exercise_status > ? ",1)}
   scope :unified_setting, -> { where("unified_setting = ?",true) }
@@ -19,13 +19,6 @@ class Exercise < ApplicationRecord
   validates :exercise_name, length: { maximum: 60, too_long: "60 characters is the maximum allowed" }
 
   after_create :create_exercise_list
-  after_destroy :destroy_other_relations
-
-  def destroy_other_relations
-    exercise_users.destroy_all
-    exercise_questions.destroy_all
-    exercise_group_settings.destroy_all
-  end
 
   def create_exercise_list
     str = ""
diff --git a/app/models/exercise_answer.rb b/app/models/exercise_answer.rb
index 96fbe17bb..11558f937 100644
--- a/app/models/exercise_answer.rb
+++ b/app/models/exercise_answer.rb
@@ -3,7 +3,7 @@ class ExerciseAnswer < ApplicationRecord
   belongs_to :user
   belongs_to :exercise_question
   belongs_to :exercise_choice, optional: true
-  has_many :exercise_answer_comments
+  has_many :exercise_answer_comments, :dependent => :delete_all
 
   scope :search_exercise_answer, lambda { |name,key| where("#{name} = ?",key)}
   scope :search_answer_users, lambda {|name,ids| where("#{name}":ids)}
@@ -11,10 +11,4 @@ class ExerciseAnswer < ApplicationRecord
   scope :exercise_answer_is_right, -> {where("score > ?",0.0)}  #判断答案是否正确，根据分数总和大于0
   scope :score_reviewed, lambda {where("score >= ?",0.0)}   #是否评分,用于判断主观题的
 
-  after_destroy :destroy_answers_relations
-
-  def destroy_answers_relations
-    exercise_answer_comments.destroy_all
-  end
-
 end
\ No newline at end of file
diff --git a/app/models/exercise_choice.rb b/app/models/exercise_choice.rb
index f4f5c5a16..72dc30c9d 100644
--- a/app/models/exercise_choice.rb
+++ b/app/models/exercise_choice.rb
@@ -1,16 +1,10 @@
 class ExerciseChoice < ApplicationRecord
 
   belongs_to :exercise_question
-  has_many :exercise_answers
-  has_many :exercise_standard_answers
+  has_many :exercise_answers, :dependent => :delete_all
+  has_many :exercise_standard_answers, :dependent => :delete_all
 
   scope :find_choice_custom, lambda {|k,v| where("#{k} = ?",v)}  #根据传入的参数查找问题
   scope :left_choice_choose, lambda {|k,v| where("#{k} > ?",v)}  #根据传入的参数查找问题
 
-  after_destroy :destroy_choices_relations
-
-  def destroy_choices_relations
-    exercise_answers.destroy_all
-    exercise_standard_answers.destroy_all
-  end
 end
\ No newline at end of file
diff --git a/app/models/exercise_question.rb b/app/models/exercise_question.rb
index c236b657c..2c9b281c3 100644
--- a/app/models/exercise_question.rb
+++ b/app/models/exercise_question.rb
@@ -4,9 +4,9 @@ class ExerciseQuestion < ApplicationRecord
   belongs_to :exercise
   belongs_to :shixun,  optional: true
 
-  has_many :exercise_choices
+  has_many :exercise_choices, :dependent => :delete_all
   has_many :exercise_answers
-  has_many :exercise_shixun_challenges
+  has_many :exercise_shixun_challenges, :dependent => :delete_all
   has_many :exercise_shixun_answers
   has_many :exercise_answer_comments
   has_many :exercise_standard_answers
@@ -15,14 +15,7 @@ class ExerciseQuestion < ApplicationRecord
   scope :find_by_custom, lambda {|k,v| where("#{k} = ?",v)}  #根据传入的参数查找问题
   scope :left_question_choose, lambda {|k,v| where("#{k} > ?",v)}  #根据传入的参数查找问题
   scope :find_objective_questions, -> {where("question_type != ?",4)}  #查找全部客观题
-  # scope :next_exercise, lambda {|k| where("question_number > ?",k).first}
-  # scope :last_exercise, lambda {|k| where("question_number < ?",k).last}
-  after_destroy :destroy_questions_relations
 
-  def destroy_questions_relations
-    exercise_choices.destroy_all
-    exercise_shixun_challenges.destroy_all
-  end
 
   def question_type_name
     case self.question_type
diff --git a/app/models/exercise_shixun_answer.rb b/app/models/exercise_shixun_answer.rb
index 72a6999d6..a9550c024 100644
--- a/app/models/exercise_shixun_answer.rb
+++ b/app/models/exercise_shixun_answer.rb
@@ -2,7 +2,7 @@ class ExerciseShixunAnswer < ApplicationRecord
   belongs_to :exercise_question
   belongs_to :user
   belongs_to :exercise_shixun_challenge
-  has_many :exercise_answer_comments
+  has_many :exercise_answer_comments, :dependent => :delete_all
   # status 0: 未通过， 1：通过
   # attr_accessible :answer_text, :score, :status
   scope :search_shixun_answers, lambda {|name,ids| where("#{name}":ids)}
@@ -10,9 +10,4 @@ class ExerciseShixunAnswer < ApplicationRecord
   scope :shixun_no_full_scores, lambda { |score| where("score > 0.0 AND score < ?",score)}
   scope :score_reviewed, lambda {where("score is not NULL AND score >= ?",0.0)}   #是否评分
 
-  after_destroy :destroy_shixun_relations
-
-  def destroy_shixun_relations
-    exercise_answer_comments.destroy_all
-  end
 end