Rails has에서and_belongs_to_many 모형 만들기

$ rails g model user name:string email:string
$ rails g model group name:string description:text
$ rails g migration create_groups_users group:references user:references

class CreateGroupsUsers < ActiveRecord::Migration
  def change
    create_table :groups_users, id: false do |t|
      t.references :group, index: true, null: false
      t.references :user, index: true, null: false
    end
  end
end

$ rake db:migrate:reset

class User < ActiveRecord::Base
  has_and_belongs_to_many :groups
end

class Group < ActiveRecord::Base
  has_and_belongs_to_many :users
end

쓸 수 있는 방법

사용 방법 예

where 방법으로 축소

User.includes(:groups).where('groups.id' => 1)

User.includes(:groups).where('groups.id' => [1, 2])

사용자와 그룹 연관

new_user = User.new(:name => 'newuser', email => '[email protected]')
new_user.groups << Group.find(1)
new_user.save

컨트롤러/뷰 사용