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ruby-on-rails has-many-through

创建 has_many :through 记录 2x 次

发布于 2024-09-02 02:33:29 字数 3708 浏览 6 评论 0 原文

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

所以当我尝试将问题绑定到其创建的测试时：

>> 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？

原文

I have models

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

So when I try to bind questions to testing on it's creation:

>> 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">

There are 6 SQL queries and 6 records in testing_questions are created. Why?

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最美的太阳 2024-09-09 02:33:29

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，并且不会创建重复的记录：

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，这与您的完全相同，除了测试问题（您没有展示）。这有帮助吗？

I have created a very simple example that handles your example:

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

.. and then i can just do the following, and no duplicate records are created:

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">]
>>

Actually that is completely the same as you have, except for the TestingQuestion (which you didn't show). Does that help?

回复收藏 0 原文

白云不回头 2024-09-09 02:33:29

第一个问题可能是联接表的命名

testing_questions

Rails 期望联接表的名称是按字母顺序排列的两个表名称的串联

question_testings

A first issue could be the naming of your join table

testing_questions

Rails expects the join table’s name to be a concatenation of the two table names in alphabetical order

question_testings

回复收藏 0 原文

反话 2024-09-09 02:33:29

查看表结构，它是表之间的 has_and_belongs_to_many 关系，无需在此处使用 has_many 和 through 选项，因为您的连接表不会有模型（除了 id 之外不存在额外的列）。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

类测试< ActiveRecord::Base

  属于：学生，：foreign_key => '用户身份'
  属于：子测试
  has_and_belongs_to_many :question_testings 
结尾

并将您的表名称更改为 Question_testings。

Looking at the table structure it is a has_and_belongs_to_many relations between the tables, there is no need to use has_many and through option here as your join table will not be having a model( no extra columns other than ids are present). No need to create a model for join table.

So, I suggest to change your models like this



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

and please change your table name as question_testings.

Please have a look at this link for more info http://guides.rubyonrails.org/association_basics.html#choosing-between-has-many-through-and-has-and-belongs-to-many

回复收藏 0 原文

洋洋洒洒 2024-09-09 02:33:29

在不查看 Rails 源代码或尝试的情况下，我建议尝试从 Question 类中删除“has_many :testing_questions”或添加一个 has_many ... :through 。现在 Rails 只与连接表有关系，但与那一侧的“真实”目标没有关系。

连接表的名称不应在此处引起任何问题。

回复收藏 0 原文

掀纱窥君容 2024-09-09 02:33:29

您的 questions 数组包含 3 个项目。当您创建 Testing 实例并指定使用 :questions => 创建它时； questions 它将把它们添加到 questions 关系中，但是因为这个关系是通过另一个关系实现的，所以必须先将它们添加到另一个关系中，导致它们被插入两次。通常，您会使用一些其他模型来表示连接表，以便将 3 条记录插入到 Questions 表中，并将 3 条记录插入到 TestQuestions 连接表中 (has_many :through)。

在我看来，这似乎是您如何定义 TestQuestions 模型的问题，但您尚未展示这一点。例如，它是否指向与 Questions 模型相同的表？