在 Rails 中建立 has_and_belongs_to_many 关系

Question

我有一个根据 Michael Hartl RoR 教程设计的用户模型，我正在尝试创建一个新的教师模型。我希望老师有很多用户，但每个用户只有一位老师。我用

创建了教师模型

class CreateTeachers < ActiveRecord::Migration
  def change
    create_table :teachers do |t|
      t.string :name
      t.string :email
      t.string :phone
      t.references :user, index: true, foreign_key: true

      t.timestamps null: false
    end
  end
end

并将 has_one :teacher 添加到 user.rb。这是 teachers.rb 模型

class Teacher < ActiveRecord::Base
  has_and_belongs_to_many :users
  validates :user_id, presence: true
  before_save   :downcase_email
  validates :name, presence: true, 
                 length: { maximum: 50 }
  VALID_EMAIL_REGEX = /\A[\w+\-.]+@[a-z\d\-]+(\.[a-z\d\-]+)*\.[a-z]+\z/i
  validates :email, presence:   true, 
                    length: { maximum: 255 },
                    format:     { with: VALID_EMAIL_REGEX },
                    uniqueness: { case_sensitive: false }
  private

    # Converts email to all lower-case.
    def downcase_email
      self.email = email.downcase
    end
end

但是在我的 teacher_test.rb 测试文件中，事情变得有点模糊。我试试这个

def setup
  @user = users(:michael)
  @user2 = users(:archer)
  @user3 = users(:lana)
  @user4 = users(:mallory)

  @teacher = Teacher.new(name: "Phred Willard",
                         email: "pwillard@test.com",
                         phone: "1234567890",
                         user_id: [@user.id, 
                                   @user2.id,
                                   @user3.id,
                                   @user4.id])
end

test "should be valid" do
  assert @uac.valid?
end

但这完全失败了。我是否正确建立了我的关系？我显然没有正确添加用户，因为该模型未通过有效性测试。我如何向该老师添加更多用户？提前致谢。

Answer 1

你的 teacher.rb 应该是

class Teacher < ActiveRecord::Base
  has_many :users
  before_save   :downcase_email
  validates :name, presence: true, 
             length: { maximum: 50 }
  VALID_EMAIL_REGEX = /\A[\w+\-.]+@[a-z\d\-]+(\.[a-z\d\-]+)*\.[a-z]+\z/i
  validates :email, presence:   true, 
                length: { maximum: 255 },
                format:     { with: VALID_EMAIL_REGEX },
                uniqueness: { case_sensitive: false }
  private

    # Converts email to all lower-case.
    def downcase_email
      self.email = email.downcase
    end
end

和user.rb

class User < ActiveRecord::Base
  belongs_to :teacher
  # rest of your code here ....
end

用户 table 中需要 teacher_id 列。

Answer 2

I would like the teacher to have many users but each user to have only one teacher

你只需要has_many / belongs_to...

#app/models/user.rb
class User < ActiveRecord::Base
   belongs_to :teacher
end

#app/models/teacher.rb
class Teacher < ActiveRecord::Base
   has_many :users
end

您需要在 users table 中添加一个 teacher_id 列（与您现在拥有的相反）：

class UpdateUsers < ActiveRecord::Migration
  def change
    change_table :users do |t|
      t.references :teacher, index: true, foreign_key: true #-> teacher_id
    end
  end
end

--

您遇到的错误是您在 teacher 上调用 user_id；它应该是 teacher_id 用户：

@teacher = Teacher.new(name: "Phred Willard",
                     email: "pwillard@test.com",
                     phone: "1234567890",
                     user_ids: [@user.id, 
                               @user2.id,
                               @user3.id,
                               @user4.id])

这应该将 @teacher 与您列出的定义的 @users 相关联。

您还需要查看 collection_singular_ids 以获得 has_many 关联，这就是您的测试失败的原因。

在 Rails 中建立 has_and_belongs_to_many 关系

Creating a has_and_belongs_to_many relationship in Rails

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