4

我有模型

class Question < ActiveRecord::Base
  WEIGHTS = %w(medium hard easy)

  belongs_to :test
  has_many :answers, :dependent => :destroy
  has_many :testing_questions
end

class Testing < ActiveRecord::Base
  belongs_to :student, :foreign_key => 'user_id'
  belongs_to :subtest
  has_many :testing_questions, :dependent => :destroy
  has_many :questions, :through => :testing_questions
end

因此，当我尝试将问题绑定到对其创建的测试时：

>> questions = Question.all
...
>> questions.count
=> 3
>> testing = Testing.create(:user_id => 3, :subtest_id => 1, :questions => questions)
  Testing Columns (0.9ms)   SHOW FIELDS FROM `testings`                              
  SQL (0.1ms)   BEGIN                                                                
  SQL (0.1ms)   COMMIT                                                               
  SQL (0.1ms)   BEGIN                                                                
  Testing Create (0.3ms)   INSERT INTO `testings` (`created_at`, `updated_at`, `user_id`, `subtest_id`) VALUES('2010-05-18 00:53:05', '2010-05-18 00:53:05', 3, 1)                                                                                                                                                        
  TestingQuestion Columns (0.9ms)   SHOW FIELDS FROM `testing_questions`                                                                                     
  TestingQuestion Create (0.3ms)   INSERT INTO `testing_questions` (`question_id`, `created_at`, `updated_at`, `testing_id`) VALUES(1, '2010-05-18 00:53:05', '2010-05-18 00:53:05', 31)                                                                                                                                  
  TestingQuestion Create (0.4ms)   INSERT INTO `testing_questions` (`question_id`, `created_at`, `updated_at`, `testing_id`) VALUES(2, '2010-05-18 00:53:05', '2010-05-18 00:53:05', 31)                                                                                                                                  
  TestingQuestion Create (0.3ms)   INSERT INTO `testing_questions` (`question_id`, `created_at`, `updated_at`, `testing_id`) VALUES(3, '2010-05-18 00:53:05', '2010-05-18 00:53:05', 31)                                                                                                                                  
  TestingQuestion Create (0.3ms)   INSERT INTO `testing_questions` (`question_id`, `created_at`, `updated_at`, `testing_id`) VALUES(1, '2010-05-18 00:53:05', '2010-05-18 00:53:05', 31)                                                                                                                                  
  TestingQuestion Create (0.3ms)   INSERT INTO `testing_questions` (`question_id`, `created_at`, `updated_at`, `testing_id`) VALUES(2, '2010-05-18 00:53:05', '2010-05-18 00:53:05', 31)                                                                                                                                  
  TestingQuestion Create (0.3ms)   INSERT INTO `testing_questions` (`question_id`, `created_at`, `updated_at`, `testing_id`) VALUES(3, '2010-05-18 00:53:05', '2010-05-18 00:53:05', 31)                                                                                                                                  
  SQL (90.2ms)   COMMIT                                                                                                                                      
=> #<Testing id: 31, subtest_id: 1, user_id: 3, created_at: "2010-05-18 00:53:05", updated_at: "2010-05-18 00:53:05">

在 testing_questions 中创建了 6 个 SQL 查询和 6 条记录。为什么？

4

5 回答 5

2

我创建了一个非常简单的示例来处理您的示例：

class Question < ActiveRecord::Base
  has_many :testing_questions
end

class Testing < ActiveRecord::Base
  has_many :testing_questions
  has_many :questions, :through => :testing_questions
end

class TestingQuestion < ActiveRecord::Base
  belongs_to :question
  belongs_to :testing
end

..然后我可以执行以下操作，并且不会创建重复记录：

Loading development environment (Rails 2.3.5)
>> q1 = Question.new
=> #<Question id: nil, title: nil, ask: nil, created_at: nil, updated_at: nil>
>> q1.title = "Dit is de eerste vraag"
=> "Dit is de eerste vraag"
>> q2 = Question.new
=> #<Question id: nil, title: nil, ask: nil, created_at: nil, updated_at: nil>
>> q2.title = "Dit is de tweede vraag"
=> "Dit is de tweede vraag"
>> q1.save
=> true
>> q2.save
=> true
>> tt = Testing.new
=> #<Testing id: nil, name: nil, description: nil, action: nil, created_at: nil, updated_at: nil>
>> tt.questions
=> []
>> tt.name = "Test1"
=> "Test1"
>> tt.questions << q1
=> [#<Question id: 1, title: "Dit is de eerste vraag", ask: nil, created_at:   "2010-05-18 19:40:54", updated_at: "2010-05-18 19:40:54">]
>> tt.questions << q2
=> [#<Question id: 1, title: "Dit is de eerste vraag", ask: nil, created_at: "2010-05-18 19:40:54", updated_at: "2010-05-18 19:40:54">, #<Question id: 2, title: "Dit is de tweede vraag", ask: nil, created_at: "2010-05-18 19:40:59", updated_at: "2010-05-18 19:40:59">]
>> tt.testing_questions
=> []
>> tt.save
=> true
>> tt.testing_questions
=> [#<TestingQuestion id: 1, question_id: 1, testing_id: 1, extra_info: nil, created_at: "2010-05-18 19:41:43", updated_at: "2010-05-18 19:41:43">, #<TestingQuestion id: 2, question_id: 2, testing_id: 1, extra_info: nil, created_at: "2010-05-18 19:41:43", updated_at: "2010-05-18 19:41:43">]
>>

实际上，这与您所拥有的完全一样，除了 TestingQuestion （您没有显示）。这有帮助吗？

于 2010-05-18T19:48:18.443 回答
0

在不查看 Rails 源代码或四处尝试的情况下，我建议尝试从 Question 类中删除 "has_many :testing_questions" 或添加 has_many ... :through 。刚才 Rails 只是与连接表有关系，但与那一侧的“真实”目标没有关系。

连接表的名称在这里应该不会造成任何问题。

于 2010-05-18T14:15:08.357 回答
0

您的questions数组包含 3 个项目。当您创建一个Testing实例并指定创建它时，:questions => questions它会将它们添加到questions关系中，但是由于这种关系是通过另一个关系，因此必须先将它们添加到另一个关系中，从而导致它们被插入两次。通常，您将有一些其他模型表示连接表，因此您将 3 条记录插入到 Questions 表中，并将 3 条记录插入到 TestingQuestions 连接表中（has_many :through）。

在我看来，这是您如何定义您的 TestingQuestions 模型的问题，您没有显示。例如，它是否指向与 Questions 模型相同的表？

于 2012-09-18T04:34:41.567 回答
0

第一个问题可能是连接表的命名

testing_questions

Rails 期望连接表的名称是按字母顺序连接的两个表名

question_testings
于 2010-05-18T06:33:17.247 回答
0

查看表结构，它是表之间的 has_and_belongs_to_many 关系，这里不需要使用 has_many 和 through 选项，因为您的连接表将没有模型（除了 ids 之外没有额外的列）。无需为连接表创建模型。

所以，我建议像这样改变你的模型



class Question < ActiveRecord::Base

  WEIGHTS = %w(medium hard easy)
  belongs_to :test

  has_many :answers, :dependent => :destroy

  has_and_belongs_to_many :question_testings 
end



class Testing < ActiveRecord::Base

  belongs_to :student, :foreign_key => 'user_id'
  belongs_to :subtest
  has_and_belongs_to_many :question_testings 
end

并将您的表名更改为 question_testings。

请查看此链接以获取更多信息http://guides.rubyonrails.org/association_basics.html#choosing-between-has-many-through-and-has-and-belongs-to-many

于 2010-05-18T12:25:29.403 回答