has_many ：通过未初始化的常量

Question

我已经阅读了有关 has_many 的文档和大量教程：通过 Rails 中的关系，但我终生无法掌握它。

我正在尝试将一个组添加到我的 current_user(devise) 中，并且我在 Group 和 User 之间有一个状态表（该组的用户状态是可更改的）。

现在每当我创建一个新组时，我都会收到一条错误消息 uninitialized constant Group::GroupUser

这是我的模型：

groupuser.rb

class GroupUser < ActiveRecord::Base
    belongs_to              :group
    belongs_to              :user
end

group.rb

class Group < ActiveRecord::Base
    has_many                            :clients
    has_and_belongs_to_many             :pictograms

    has_many :group_users
    has_many :users, :through => :group_users

    accepts_nested_attributes_for :clients

    validates_length_of                 :name,  :minimum => 5
    validates_presence_of               :name
    validates_presence_of               :background
    validates_presence_of               :clocktype
end

用户.rb

class User < ActiveRecord::Base
  # Include default devise modules. Others available are:
  # :token_authenticatable, :confirmable,
  # :lockable, :timeoutable and :omniauthable
  devise :database_authenticatable, :registerable,
         :recoverable, :rememberable, :trackable, :validatable


  validates_presence_of   :first_name
  validates_presence_of   :last_name
  validates               :email, presence: true, uniqueness: true

  has_many :group_users
  has_many :groups, :through => :group_users

  has_attached_file :avatar, :styles => { 
                                :medium => "300x300#", 
                                :thumb => "100x100#" 
                             }
  validates_attachment_content_type :avatar, :content_type => ['image/jpg', 'image/png', 'image/jpeg']

  validates_attachment :avatar,
                  :size => { :in => 0..1.megabytes }

  def completeName
    "#{self.first_name} #{self.last_name}"
  end
end

以及来自 schema.rb

的相关内容

  create_table "group_users", id: false, force: true do |t|
    t.integer "group_id"
    t.integer "user_id"
    t.integer "status",   default: 0
  end

  add_index "group_users", ["group_id"], name: "index_group_users_on_group_id"
  add_index "group_users", ["user_id"], name: "index_group_users_on_user_id"

  create_table "groups", force: true do |t|
    t.string   "name"
    t.integer  "clocktype"
    t.string   "background"
    t.datetime "created_at"
    t.datetime "updated_at"
  end
  create_table "users", force: true do |t|
    t.string   "first_name"
    t.string   "last_name"
    t.string   "password"
    t.string   "avatar_file_name"
    t.string   "avatar_content_type"
    t.integer  "avatar_file_size"
    t.datetime "avatar_updated_at"
    t.datetime "created_at"
    t.datetime "updated_at"
    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
    t.datetime "current_sign_in_at"
    t.datetime "last_sign_in_at"
    t.string   "current_sign_in_ip"
    t.string   "last_sign_in_ip"
  end

  add_index "users", ["email"], name: "index_users_on_email", unique: true
  add_index "users", ["reset_password_token"], name: "index_users_on_reset_password_token", unique: true

最后。 引发错误的行

@group.users << current_user

Answer 1

我看到的问题是你对GroupUser的命名

我们一直使用连接模型，并且我们也用下划线命名它们：

group_user.rb
class GroupUser < ActiveRecord::Base
  belongs_to :group
  belongs_to :user
end

未初始化的常量错误将由模型未正确加载引起，我想这将是由于命名问题。如果这不起作用，您应该在关系声明中使用 :class_name 参数引用模型：

  has_many :group_users, :class_name => 'GroupUser'
  has_many :groups, :through => :group_users

---

更新

We wanted to call extra attributes 来自 join 模型，发现是这样的：

#app/models/message.rb
has_many :image_messages, :class_name => 'ImageMessage'
has_many :images, -> { select("#{Image.table_name}.*, #{ImageMessage.table_name}.caption AS caption") }, :class_name => 'Image', :through => :image_messages, dependent: :destroy

这使用了 select 方法，您可以在创建 ActiveRecord 关联时使用该方法，就像我们 discovered from this RailsCast 一样，您可以使用它在查询中创建 alias 列

对你来说，你不妨试试这个：

#app/models/user.rb
has_many :group_users, :class_name => 'Groupuser'
has_many :groups, -> { select("#{User.table_name}.*, #{Groupuser.table_name}.status AS status") }, :class_name => 'Group', :through => :group_users, dependent: :destroy