2xbelongs_to，B唯一

Question

def User 
    has_many :conversation_participants 
end 

def Conversation 
    has_many :conversation_participants 
end 

def ConversationParticipant 
    belongs_to :conversation 
    belongs_to :user 
end 

我想將驗證添加到ConversationParticipant，以便一個對話（conversation_id）只能存在一個相同用戶（user_id）的記錄。所以這將是無效的：

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

任何關鍵字，描述這個問題（未來Googlin'）讚賞。

編輯：一些代碼

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，：範圍=> [：conversation_id]

個

或者性感驗證：

驗證：USER_ID，：唯一=> {：範圍=> [：conversation_id]}

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

Answer 2

可以傳遞一個：uniq的進入的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).