Ruby on Rails - 与模型的多对多关联

Question

Im trying to create a messaging system in Rails. The association of users to conversations should be of kind many to many, so that users can have multiple conversations and conversations multiple users. Therfore i created the three tables users, conversation_relations and conversations and a model for each.

the models look like:

class User < ActiveRecord::Base
    has_many :conversation_relations
    has_many :conversations, through: :conversation_relations
end

class Conversation < ActiveRecord::Base
    has_many :conversation_relations
    has_many :users, through: :conversation_relations
end

and

class ConversationRelation < ActiveRecord::Base
    belongs_to :user
    belongs_to :conversation
end

My problem is, when i try to assign multiple users to a conversation, the entry in the conversation_relations table is updated instead of creating a new entry.

eg (on console):

conversation = Conversation.create()
user1 = User.find(1)
user2 = User.find(2)
relation = ConversationRelation.new()

conversation.conversation_relations << relation
user1.conversation_relations << relation
user2.conversation_relations << relation

The problem occurs in the last line, because it updates the row created by user1.conversation_relations << relation instead of creating a new one. Do i need to change something in the models or is the assignment awkward?

Answer 1

Instead of conversation.conversation_relations << relation

you must use conversation.conversation_relations.create(params)

With the value returned by the given option you can use now << and the new conversation_relation will be added

Answer 2

Just do

user1.conversations << conversation
# or
conversation.users << user1

no need to do ConversationRelation.new, rails will take care of this