2xbelongs_to，B的独特之处

Question

def User
  has_many :conversation_participants
end

def Conversation
  has_many :conversation_participants
end

def ConversationParticipant
  belongs_to :conversation
  belongs_to :user
end

我想向ConversationParticipant添加验证，以便只存在一个对话（conversation_id）的同一用户（user_id）的一条记录。所以这将是无效的：

id  user_id  conversation_id
1   1        1
2   2        1
3   1        1 # <-- invalid
4   3        1

任何描述此问题的关键字（对于未来的Googlin'）都表示赞赏。

编辑：一些代码

c = Conversation.first
c.conversation_participants.build(:user => User.first)
c.save # => true

c.conversation_participants.build(:user => User.first)
c.save # => false

Answer 1

  

validates_uniqueness_of：user_id，：scope =＆gt; [：conversation_id]

或性感验证：

  

验证：user_id，：uniqueness =＆gt; {：scope =＆gt; [：conversation_id]}

http://ar.rubyonrails.org/classes/ActiveRecord/Validations/ClassMethods.html#M000086

Answer 2

您可以将：uniq传递给has_many：

def User
  has_many :conversation_participants, :uniq => true
end

def Conversation
  has_many :conversation_participants, :uniq => true
end

def ConversationParticipant
  belongs_to :conversation
  belongs_to :user
end

RoR Associations (uniqueness constraint is about 3/4 of the way down).