ruby-on-rails - before_destroy 不是从 update_attributes 触发的

Question

我有一个学生，他有很多类(class)。在 student#update 操作和表单中，我接受 course_ids 列表。当该列表更改时，我想调用某个函数。如果 update_attributes 创建一个 course_student，我的代码会被调用，但如果 update_attributes 破坏一个 course_student，则不会被调用。我可以让它触发，还是我必须自己检测变化？

# app/models/student.rb
class Student < ActiveRecord::Base
  belongs_to :teacher
  has_many :grades
  has_many :course_students, :dependent => :destroy
  has_many :courses, :through => :course_students
  has_many :course_efforts, :through => :course_efforts

  # Uncommenting this line has no effect:
  #accepts_nested_attributes_for :course_students, :allow_destroy => true

  #attr_accessible :first_name, :last_name, :email, :course_students_attributes

  validates_presence_of :first_name, :last_name
...
end

# app/models/course_student.rb
class CourseStudent < ActiveRecord::Base
  after_create  :reseed_queues
  before_destroy :reseed_queues

  belongs_to :course
  belongs_to :student

  private

  def reseed_queues
    logger.debug "******** attempting to reseed queues"
    self.course.course_efforts.each do |ce|
      ce.reseed
    end
  end

end

# app/controllers/students_controller.rb

  def update
    params[:student][:course_ids] ||= []
    respond_to do |format|
      if @student.update_attributes(params[:student])
        format.html { redirect_to(@student, :notice => 'Student was successfully updated.') }
        format.xml  { head :ok }
      else
        format.html { render :action => "edit" }
        format.xml  { render :xml => @student.errors, :status => :unprocessable_entity }
      end
    end
  end

Answer 1

事实证明，此行为已记录在案，就在 上。 has_many 方法。来自 API 文档:

collection=objects Replaces the collections content by deleting and adding objects as appropriate. If the :through option is true callbacks in the join models are triggered except destroy callbacks, since deletion is direct.

我不确定“因为删除是直接的”是什么意思，但我们知道了。