使用一个模型和另一个模型的两个属性在 Rails 中创建联接 Table

Question

正在尝试创建一个连接 table，该连接在一个模型上采用两个属性，并将它们与第二个模型的 ID 相关联。由于持续刷新过程，无法使用第一个模型的 ID，该过程重新排序该模型 table (ConstantlyRefreshingModels) 上的行。

class ConstantlyRefreshingModels < ApplicationRecord
  attr_accessor :home_id, :chair, :floor, :number 
  has_and_belongs_to_many :family
end 

class Family < ApplicationRecord
  attr_accessor :bread_winner
  has_and_belongs_to_many :constantlyrefreshingmodel
end

class CreateFamilyModelThatConstantlyRefreshesJoinTable < ActiveRecord::Migration[5.0]
  def change
    create_join_table :families, :constantlyrefreshingmodel
  end
end

正在寻找如下所示的联接 table：

home_id | number | family_id
-----------------------------
    2   | '3003' |    4
    1   | '2100' |    1

然后这对公开数据有效：

new_home = constantlyrefreshingmodel.where(home_id: 2)
new_home.families == 4 == true

关于创建连接 table 和声明关联有什么建议吗？

Answer 1

您需要 has_many :through Association 而不是 has_and_belongs_to_many，因为您在连接模型中有其他属性 (:number)

You should use has_many :through if you need validations, callbacks or extra attributes on the join model. Section 2.8

试试这个方法：

class Home < ApplicationRecord
  has_many :points
  has_many :families, through: :points
end

# Point is your join model, AKA ConstantlyRefreshingModel
class Point < ApplicationRecord
  belongs_to :family
  belongs_to :home

  validates :points, presence: true # Or some other validation, :number in your question.
end

class Family < ApplicationRecord
  has_many :points
  has_many :houses, through: :points
end

加入table迁移：

class CreatePoints < ActiveRecord::Migration[5.2]
  def change
    create_table :points do |t|
      t.references :home,   foreign_key: true, null: false
      t.references :family, foreign_key: true, null: false
      t.string     :points, null: false

      t.timestamps
    end
  end
end

例如有以下数据：

home_1 = Home.create(id: 1)  # home with an id of 1
home_2 = Home.create(id: 2)  # home with an id of 2

family_4 = Family.create(id: 4) # family with an id of 4
family_1 = Family.create(id: 1) # family with an id of 1

Point.create(points: "3003", home: home_2, family: family_4)
Point.create(points: "2100", home: home_1, family: family_1)

然后：

points = Point.where(home: home_2)  # you get a collection of all points assigned to house with ID: 2
points.first.family                 # family with an id of 4

揭露 :home 与 id: 2 和数字 3003 指向 id: 4

的家庭

home = Home.find(2)
home.families.ids # 4
home.points.first # 3003

要公开具有 id: 4 的家庭与 ID 为 2 且编号为 3003 的家庭相关联。

family = Family.find(4)
family.homes.ids     # 2
family.points.first  # 3003

此外，attr_accessor、attr_reader 和 attr_writer 在 Rails 5.1 中已弃用。参见 this post

使用一个模型和另一个模型的两个属性在 Rails 中创建联接 Table

Creating Join Table in Rails with One Model and Two Attributes on Another Model

model

ruby-on-rails

associations

has-and-belongs-to-many