ruby-on-rails - 关系模型未按预期工作

Question

我使用迁移创建了以下 Active Record 架构，但关系与架构不对应。我尝试过重置、删除、创建和迁移，但在 Rails C 中，如果我创建一个用户 u.User.create!(...)，然后查询 u.groups 或 u.genres，我会得到“未定义的方法”

谢谢你的帮助

ActiveRecord::Schema.define(version: 20180603211047) do

  # These are extensions that must be enabled in order to support this database
  enable_extension "plpgsql"

  create_table "genres", force: :cascade do |t|
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
    t.string "tag"
    t.bigint "user_id"
    t.index ["user_id"], name: "index_genres_on_user_id"
  end

  create_table "genres_users", id: false, force: :cascade do |t|
    t.bigint "user_id", null: false
    t.bigint "genre_id", null: false
  end

  create_table "groups", force: :cascade do |t|
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
    t.string "name"
    t.bigint "user_id"
    t.index ["user_id"], name: "index_groups_on_user_id"
  end

  create_table "groups_users", id: false, force: :cascade do |t|
    t.bigint "user_id", null: false
    t.bigint "group_id", null: false
  end

  create_table "playlists", force: :cascade do |t|
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
    t.string "name"
    t.string "link"
    t.text "description"
    t.bigint "group_id"
    t.index ["group_id"], name: "index_playlists_on_group_id"
  end

  create_table "users", force: :cascade do |t|
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
    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.string "name"
    t.string "token"
    t.date "birthday"
    t.string "link"
    t.string "playlistId"
    t.string "country"
    t.index ["email"], name: "index_users_on_email", unique: true
    t.index ["reset_password_token"], name: "index_users_on_reset_password_token", unique: true
  end

  add_foreign_key "genres", "users"
  add_foreign_key "groups", "users"
  add_foreign_key "playlists", "groups"
end

这里是模型：

class User < ApplicationRecord
  # Include default devise modules. Others available are:
  # :confirmable, :lockable, :timeoutable and :omniauthable
  devise :database_authenticatable, :registerable,
         :recoverable, :rememberable, :trackable, :validatable
    #before_action :authenticate_user!
    has_and_belongs_to_many :genres, :through => :genres_users
    has_and_belongs_to_many :groups, :through => :groups_users
    include Enumerable
end

class Genre < ApplicationRecord
    has_and_belongs_to_many :users, :through => :genres_users
end

class Group < ApplicationRecord
    has_and_belongs_to_many :users, :through => :groups_users
    has_one :playlist
end

class Playlist < ApplicationRecord
    belongs_to :group
end

关系是组有用户，用户有流派（最喜欢的流派！），这些是通过连接表（每个用户有多个流派和每个用户多个组）具有和属于关系。每个组都有一个播放列表，并且会有多个播放列表

标签： ruby-on-railsactiverecord

Answer 1

[在OP澄清后编辑]

关系是组有用户，用户有流派（最喜欢的流派！），这些是通过连接表（每个用户有多个流派和每个用户多个组）具有和属于关系。每个组都有一个播放列表，并且会有多个播放列表

首先，您不需要user_id关于组或流派的专栏，因为这不是设置的工作方式。

class Genre < ApplicationRecord
  has_many :favorite_genres
  has_many :users, through: :favorite_genres
  [... other stuff]
end


class User < ApplicationRecord
  has_many :group_memberships
  has_many :groups, through: :group_memberships

  has_many :favorite_genres
  has_many :users, through: :favorite_genres

  [... other stuff]
end

class Group < ApplicationRecord
  has_many :group_memberships
  has_many :users, through: :group_memberships

  has_many :playlists
  [... other stuff]
end

class Playlist < ApplicationRecord
  belongs_to :group
end

class GroupMemberships < ApplicationRecord
  belongs_to :user
  belongs_to :group
  [... other stuff]
end

class FavoriteGenres < ApplicationRecord
  belongs_to :user
  belongs_to :genre
  [... other stuff]
end

因此，您将分组删除 user_id 列。连接发生在 :group_memberships（以前称为 users_groups 的表）中，它是一个 user_id、一个 group_id，然后您可以根据需要拥有其他元数据列（例如，管理员布尔/角色等）。这被称为“有很多通过”关系（http://guides.rubyonrails.org/association_basics.html#the-has-many-through-association）

同样，用户最喜欢的流派是通过直通关系设置的。因此，您将拥有一个单独的数据库表和模型文件，用于连接。

add_foreign_key我认为你在这个级别根本不需要你的电话，也不需要你的许多索引。您可能会做更多的急切加载或可能在整个连接表上添加索引，并且您会在架构中执行以下操作：

t.index ["user_id", "genre_id"], name: "index_favorite_genres_on_user_id_and_genre_id"

请记住，belongs_to现在创建了一个验证，以便在 5.x 中出现。您可以通过在模型中添加该行来覆盖它optional: true，例如belongs_to :foo, optional: true

综上所述，这是您的新架构：

create_table "genres", id: :serial, force: :cascade do |t|
  t.string "tag"
  t.datetime "created_at", null: false
  t.datetime "updated_at", null: false
end

create_table "groups", id: :serial, force: :cascade do |t|
  t.string "name"
  t.datetime "created_at", null: false
  t.datetime "updated_at", null: false
end

create_table "favorite_genres", id: false, force: :cascade do |t|
  t.bigint "user_id", null: false
  t.bigint "genre_id", null: false
end

create_table "groups_memberships", id: false, force: :cascade do |t|
  t.bigint "user_id", null: false
  t.bigint "group_id", null: false
end

create_table "playlists", id: :serial, force: :cascade do |t|
  t.datetime "created_at", null: false
  t.datetime "updated_at", null: false
  t.string "name"
  t.string "link"
  t.text "description"
  t.bigint "group_id"
  t.index ["group_id"], name: "index_playlists_on_group_id"
end

create_table "users", id: :serial, force: :cascade do |t|
  t.datetime "created_at", null: false
  t.datetime "updated_at", null: false
  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.string "name"
  t.string "token"
  t.date "birthday"
  t.string "link"
  t.string "playlistId"
  t.string "country"
  t.index ["email"], name: "index_users_on_email", unique: true
  t.index ["reset_password_token"], name: "index_users_on_reset_password_token", unique: true
end

试一试（我没有在应用程序中构建它，因此代码中可能存在一些错误），您现在应该可以运行控制台了：

u = User.create([values])
u.genres (should return nil until you create some relationships)

等等