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These are my classes & relations

class User
  has_many :conversation_participants
  has_many :conversations, :through => :conversation_participants
end

class ConversationParticipant
  belongs_to :user
  belongs_to :conversation
end

class Conversation
  has_many :messages
  has_many :conversation_participants
  has_many :users, :through => :conversation_participants
end

So when I want to create a conversation between user_ids 12 and 15, I first want to check if a conversation between these two already exists. So what I need to find is this:

ConversationParticipants where user_id IN (12, 15) AND "both conversationparticipant rows have the same conversation id"

I lack the proper words to explain this query but I think everyone will get what I mean. "Does a conversation between these two users exist already?". I know neither how to do it in SQL nor Rails so any answer is appreciated.

EDIT The id of the conversation would not be known. I need to find if a conversation between those two user_ids exist.

Thanks -- Emil

Emil Ahlbäck
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2 Answers2

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class User
  has_many :conversations
  has_many :conversation_participants
  has_many :joined_conversations, :through => :conversation_participants, :source => :conversation
end

class ConversationParticipant
  belongs_to :user
  belongs_to :conversation
end

class Conversation
  belongs_to :user
  has_many :conversation_participants
  has_many :speakers, :through => :conversation_participants, :source => :user
end
VvDPzZ
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  • belongs_to :user would imply that there's a user_id column in the conversations table, which there is not. I'll add the schema sometime tonight when I'm at my computer. – Emil Ahlbäck Apr 16 '12 at 13:13
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You can try this 

 @result = ConversationParticipants.where("user_id in ? AND conversation_id=?",[1,2,3,4],2)
Kashiftufail
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