ruby-on-rails - ActiveRecord::HasManyThroughOrderError: 不能有 has_many :through 关联

Question

在我的 Rails 应用程序中，我正在尝试创建一个系统，该系统将奖励用户取得各种成就的徽章

创建了一个表 'user_badges'

迁移:

class CreateUserBadges < ActiveRecord::Migration[5.1]
  def change
    create_table :user_badges do |t|

    t.references :user, foreign_key: true
    t.references :badge, foreign_key: true

    t.timestamps
    end
  end
end

模型用户徽章:

class UserBadge < ApplicationRecord

  belongs_to :user
  belongs_to :badge

end

модель 徽章:

class Badge < ApplicationRecord
  has_many :users, through: :user_badges
  has_many :user_badges
end

模型用户:

class User < ApplicationRecord
  ...

  has_many :badges, through: :user_badges
  has_many :user_badges

  ...
end

当我尝试为用户添加徽章时:

b = Badge.create(title: 'first')

User.last.badges << b

我收到这个错误:

ActiveRecord::HasManyThroughOrderError: Cannot have a has_many 
:through association 'User#badges' which goes through 
'User#user_badges' before the through association is defined.

还有当我简单地打电话时:

User.last.badges

同样的错误:

ActiveRecord::HasManyThroughOrderError: Cannot have a has_many 
:through association 'User#badges' which goes through 
'User#user_badges' before the through association is defined.

Answer 1

先定义has_many关联，再添加through:关联

class UserBadge < ApplicationRecord
  belongs_to :user
  belongs_to :badge
end

class Badge < ApplicationRecord
  has_many :user_badges # has_many association comes first
  has_many :users, through: :user_badges #through association comes after
end


class User < ApplicationRecord
  ...
  has_many :user_badges
  has_many :badges, through: :user_badges
  ...
end