Question

I have set up a twitter-like following model. Users can all subscribe to each other. I am getting an error in my users controller when trying to create the relationship.

user.rb:

has_many :subscriptions
has_many :providers, :through => :subscriptions

has_many :followings, :class_name => "Subscription"
has_many :followers, :through => :followings

subscription.rb

belongs_to :provider, :class_name => 'User', :foreign_key => "provider_id"
belongs_to :follower, :class_name => 'User', :foreign_key => "follower_id"

users_controller.rb

69 def follow
70   logger.debug params.to_yaml
71   @user = User.find(params["user_id"])
72   logger.debug @user.to_yaml
73   if current_user.providers << @user
74     flash[:notice] = "Subscribed"
75   else
76     flash[:error] = "Unable to subscribe."
77   end
78 end

This is the error when I call follow:

ActiveRecord::UnknownAttributeError (unknown attribute: user_id):
  app/controllers/users_controller.rb:73:in `follow'

I have verified that I ran rake db:migrate – the subscription table has two fields provider_id and follower_id. Can anyone help me with the error and explain why it is looking for a ‘user_id’ attribute?

Update:

show.html.erb:

<%= button_to "Subscribe", user_follow_path(@user), :remote => true %>

routes.rb:

resources :users do
  resources :locations
  resources :saved_events
  resources :saved_locations
  post "follow"
end

rake routes | grep follow:

user_follow POST     /users/:user_id/follow(.:format)                    {:action=>"follow", :controller=>"users"}

Answer 1

Using Michael Hartl’s tutorial as a guide, I came up with this solution, which fixes the data model so that collection functions work as they should.

Make the provider id accessible and remove the foreign keys in the subscription model.

subscription.rb:

attr_accessible :provider_id
belongs_to :provider, :class_name => 'User'
belongs_to :follower, :class_name => 'User'

Add foreign keys for subscriptions and reverse_subscriptions in the user model.

user.rb:

has_many :subscriptions, :foreign_key => "subscriber_id", :dependent => :destroy
has_many :subscribed_to, :through => :subscriptions, :source => :provider

has_many :reverse_subscriptions, :class_name => "Subscription", :foreign_key => "provider_id", :dependent => :destroy
has_many :followers, :through => :reverse_subscriptions

I also added helper methods to the user model.

user.rb:

def following?(provider)
  subscriptions.find_by_provider_id(provider)
end

def follow!(provider)
  subscriptions.create!(:provider_id => provider.id)
end

def unfollow!(provider)
  subscriptions.find_by_provider_id(provider).destroy
end

Then, in the controller, we can call follow! or unfollow!

user_controller.rb:

...
current_user.unfollow!(@user)
...
current_user.follow!(@user)
...