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我有一些参加测验的用户。我跟踪他们选择的结果。我需要弄清楚如何让他们更改他们的测验提交。如果我只是将答案联系起来，他们会回答两次这个问题。建立数据很复杂，ActiveRecord 是否提供了一种方法来处理这个问题？

整个示例将在独立文件中运行。

这是我的架构：

require 'active_record'

ActiveRecord::Base.establish_connection adapter: 'sqlite3', database: ':memory:'

ActiveRecord::Schema.define do
  self.verbose = false

  create_table :users do |t|
    t.string :name
  end

  create_table :questions do |t|
    t.string :name
  end

  create_table :question_results do |t|
    t.string  :name
    t.integer :question_id
  end

  create_table :question_results_users do |t|
    t.integer :user_id
    t.integer :question_result_id
  end
end

这是我的模型：

class User < ActiveRecord::Base
  has_and_belongs_to_many :question_results
  has_many :questions, through: :question_results
end

class Question < ActiveRecord::Base
  has_many :question_results
end

class QuestionResult < ActiveRecord::Base
  belongs_to :question
  has_and_belongs_to_many :users
end

让我们提出三个问题和一些答案：

Question.create! name: "What's your favourite movie?" do |question|
  question.question_results.build name: 'Gattaca'
  question.question_results.build name: 'Super Troopers'
end

Question.create! name: 'Who do you want to be president?' do |question|
  question.question_results.build name: 'Barack Obama'
  question.question_results.build name: 'Mitt Romney'
  question.question_results.build name: 'Mickey Mouse'
end

Question.create! name: "What's your favourite colour?" do |question|
  question.question_results.build name: 'black'
  question.question_results.build name: 'green'
end

让我们创建一个用户：

jim = User.create! name: 'Jim'
jim.question_results << QuestionResult.find_by_name('Gattaca')
jim.question_results << QuestionResult.find_by_name('Barack Obama')
jim.question_results << QuestionResult.find_by_name('black')

jim.question_results                  # => [#<QuestionResult id: 1, name: "Gattaca", question_id: 1>, #<QuestionResult id: 3, name: "Barack Obama", question_id: 2>, #<QuestionResult id: 6, name: "black", question_id: 3>]
jim.question_results.map(&:question)  # => [#<Question id: 1, name: "What's your favourite movie?">, #<Question id: 2, name: "Who do you want to be president?">, #<Question id: 3, name: "What's your favourite colour?">]

现在 Jim 改变了主意，他决定喜欢 Super Troopers 并且不想投票，但他仍然喜欢黑色。我如何在不让他多次回答问题的情况下更新它？

# pretend we're in a controller here (also note that I can change the format of the data, if there is something more convenient)
posted_from_form = {
  questions: {
    Question.all[0].id => 'Super Troopers',
    Question.all[1].id => '',
    Question.all[2].id => 'black',
  }
}
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1 回答 1

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首先让我们更改数据的格式，以便结果是 id 形式而不是 name 形式：

posted_from_form = {
  questions: {
    Question.all[0].id => QuestionResult.find_by_name('Super Troopers').id.to_s,
    Question.all[1].id => '',
    Question.all[2].id => QuestionResult.find_by_name('black').id,
  }
}

然后您可以直接设置 id，ActiveRecord 将处理所有复杂性：

jim.question_result_ids = posted_from_form[:questions].values # => ["2", "", 6]
jim.question_results # => [#<QuestionResult id: 6, name: "black", question_id: 3>, #<QuestionResult id: 2, name: "Super Troopers", question_id: 1>]
于 2012-08-30T17:39:49.707 回答