ruby-on-rails - Rails 3 - dependent => :delete_all doesn't work. 为什么？

Question

我的项目中几乎没有模型。其中有一些:Qualification 和 Curriculum。 Qualification 有 child (类(class))。我想确保当我删除 Qualification 时，我删除了它的所有子项。这是我的代码:

# Table name: qualifications
#
#  id         :integer         not null, primary key
#  subject_id :integer
#  teacher_id :integer
#  created_at :datetime        not null
#  updated_at :datetime        not null
class Qualification < ActiveRecord::Base
  belongs_to :subject
  belongs_to :teacher

  has_many :curriculums, :dependent => :delete_all
  has_many :school_classes, :through => :curriculums
end

#  id               :integer         not null, primary key
#  school_class_id  :integer
#  qualification_id :integer
#  created_at       :datetime        not null
#  updated_at       :datetime        not null
class Curriculum < ActiveRecord::Base
  belongs_to :school_class
  belongs_to :qualification

  has_one :result

  has_many :timetables
end

如您所见，我尝试在资格模型中使用 :dependent => :delete_all。但它不起作用。为什么？

更新:

我在编辑时通过取消选中 View 中的复选框来删除资格:

<div class="control-group"> 
  <%= f.label :subject_ids, "Teacher can teach such subjects in the school", 
              :class => "control-label" %>               

  <div class="controls">
    <table class="table table-bordered table-striped">
      <thead>
        <tr>
          <th>Choose</th>
          <th>Subject</th>
        </tr>
      </thead>
      <tbody>
        <%= hidden_field_tag "teacher[subject_ids][]", nil %>                         <%# We use hidden field because it doesn't submit unchecked fields. So, we pass nil and nothing will be submitted.%>

        <% @subjects.each do |subject| %>                                             
          <tr>                                                                        
            <td>                                                                      
              <%= check_box_tag "teacher[subject_ids][]",                             # [] brackets tells that this is array.
                                subject.id,                                           # Value of checkbox.
                                @teacher.subject_ids.include?(subject.id),            # Here we automatically check checkboxes.
                                id: dom_id( subject ) %>                              <%# Give unique id for each value. 'dom_id' is Rails helper. We will have ids like: 'subject_1', 'subject_2' and etc. %>
            </td>                                                                     
            <td>                                                                      
              <%= label_tag dom_id( subject ), subject.subject_name %>                <%# Put name of subject. %>
            </td>
          </tr>
        <% end %>
      </tbody>
    </table>
  </div>
 </div>

这里是更多信息:

class Teacher < ActiveRecord::Base  
  has_many :qualifications
  has_many :subjects, :through => :qualifications
end

class Subject < ActiveRecord::Base
  has_many :qualifications
  has_many :teachers, :through => :qualifications  
end

这是我更新模型时的 SQL 代码:

Started PUT "/teachers/2" for 127.0.0.1 at 2012-06-03 18:34:44 +0400
Processing by TeachersController#update as HTML
  Parameters: {"utf8"=>"✓", "authenticity_token"=>"ZJNNV9/TO6k18O1Ar1kpkU+PWbd7btHm9Tc067iMNO4=", "teacher"=>{"teacher_last_name"=>"Last", "teacher_first_name"=>"First", "teacher_middle_name"=>"Middle", "teacher_sex"=>"m", "teacher_birthday"=>"1980-12-01", "teacher_phone_attributes"=>{"teacher_mobile_number"=>"88283686", "teacher_home_number"=>"5112787", "id"=>"2"}, "teacher_education_attributes"=>{"teacher_education_university"=>"Mmm", "teacher_education_year"=>"1970-01-01", "teacher_education_graduation"=>"Graduated", "teacher_education_speciality"=>"Math", "id"=>"2"}, "teacher_category"=>"1st", "subject_ids"=>["", "4", "3", "1"]}, "commit"=>"Update", "id"=>"2"}
  User Load (0.5ms)  SELECT "users".* FROM "users" WHERE "users"."id" = 2 LIMIT 1
  Teacher Load (0.4ms)  SELECT "teachers".* FROM "teachers" WHERE "teachers"."id" = $1 LIMIT 1  [["id", "2"]]
   (0.1ms)  BEGIN
  Subject Load (0.5ms)  SELECT "subjects".* FROM "subjects" WHERE "subjects"."id" IN (4, 3, 1)
  Subject Load (0.5ms)  SELECT "subjects".* FROM "subjects" INNER JOIN "qualifications" ON "subjects"."id" = "qualifications"."subject_id" WHERE "qualifications"."teacher_id" = 2
  SQL (0.4ms)  DELETE FROM "qualifications" WHERE "qualifications"."teacher_id" = 2 AND "qualifications"."subject_id" = 2
  TeacherPhone Load (0.4ms)  SELECT "teacher_phones".* FROM "teacher_phones" WHERE "teacher_phones"."teacher_id" = 2 LIMIT 1
  TeacherEducation Load (0.4ms)  SELECT "teacher_educations".* FROM "teacher_educations" WHERE "teacher_educations"."teacher_id" = 2 LIMIT 1
   (24.1ms)  COMMIT
Redirected to http://0.0.0.0:3000/teachers
Completed 302 Found in 57ms (ActiveRecord: 27.2ms)

Answer 1

尝试:

:dependent => :destroy 

代替 :dependent => :delete_all