Active Record Associations

Active Record Associations

关联关系：1：N

class Author < ApplicationRecord
  has_many :books, dependent: :destroy
end

class Book < ApplicationRecord
  belongs_to :author
end

创建的时候，需要进行关联：

@book = Book.create(published_at: Time.now, author_id: @author.id)

@book = @author.books.create(published_at: Time.now)

这时：删除作者及其所有书籍要容易得多：

@author.destroy

对应的migration应该是这样；

class CreateBooks < ActiveRecord::Migration[7.0]
  def change
    create_table :authors do |t|
      t.string :name
      t.timestamps
    end

    create_table :books do |t|
      t.belongs_to :author
      t.datetime :published_at
      t.timestamps
    end
  end
end

关联关系  1：1

class Supplier < ApplicationRecord
  has_one :account
end

对应的migration是：

class CreateSuppliers < ActiveRecord::Migration[7.0]
  def change
    create_table :suppliers do |t|
      t.string :name
      t.timestamps
    end

    create_table :accounts do |t|
      t.belongs_to :supplier
      t.string :account_number
      t.timestamps
    end
  end
end

比较复杂的是：

has_many :through

class Physician < ApplicationRecord
  has_many :appointments
  has_many :patients, through: :appointments
end

class Appointment < ApplicationRecord
  belongs_to :physician
  belongs_to :patient
end

class Patient < ApplicationRecord
  has_many :appointments
  has_many :physicians, through: :appointments
end

对应的migrate是：

class CreateAppointments < ActiveRecord::Migration[7.0]
  def change
    create_table :physicians do |t|
      t.string :name
      t.timestamps
    end

    create_table :patients do |t|
      t.string :name
      t.timestamps
    end

    create_table :appointments do |t|
      t.belongs_to :physician
      t.belongs_to :patient
      t.datetime :appointment_date
      t.timestamps
    end
  end
end