ruby-on-rails - 使用主键从数据库中的第三个模型检索数据

Question

我想使用下面架构中的主键访问当前用户的相册。我有如下用户、乐队和专辑模型......

class User < ActiveRecord::Base
  devise :database_authenticatable, :registerable,
     :recoverable, :rememberable, :trackable, :validatable

  has_many :bands
end

---

class Band < ActiveRecord::Base
  has_many :albums
  has_many :users
end

---

class Album < ActiveRecord::Base
  belongs_to :band
end

架构如下...

create_table "albums", force: true do |t|
  t.string   "name"
  t.string   "releaseDate"
  t.string   "artWorkUrl"
  t.integer  "band_id"
  t.datetime "created_at"
  t.datetime "updated_at"
end

create_table "bands", force: true do |t|
  t.string   "name"
  t.datetime "created_at"
  t.datetime "updated_at"
  t.integer  "user_id"
end

create_table "users", force: true do |t|
  t.string   "email",                  default: "", null: false
  t.string   "encrypted_password",     default: "", null: false
  t.string   "reset_password_token"
  t.datetime "reset_password_sent_at"
  t.datetime "remember_created_at"
  t.integer  "sign_in_count",          default: 0,  null: false
  t.datetime "current_sign_in_at"
  t.datetime "last_sign_in_at"
  t.string   "current_sign_in_ip"
  t.string   "last_sign_in_ip"
  t.datetime "created_at"
  t.datetime "updated_at"
end

我正在尝试在相册 Controller 中使用以下方法...

def albums
  @albums = current_user.bands.albums
end

抱歉，我确定这是一个菜鸟问题。我知道这应该是通过用户 --> 乐队 --> 专辑的简单主键访问，使用 user_id 和 band_id 但无法通过乐队填充当前用户专辑。非常感谢任何见解。

Answer 1

def albums
  band_ids = current_user.bands.map(&:id)
  @albums = Album.where(band_id: band_ids)
end

通过分离查询，您没有n+1 问题:What is SELECT N+1?