Question

I have a Rails app where users can follow one another. I’ve just discovered a bug where a user can follow a person more than once.

If a user isn’t following someone, and opens the website in two different windows and clicks ‘follow’ in both windows, they are following the person twice.

In my controller I have a condition which I thought would prevent this from happening but it doesn’t work.

  def follow
   unless follows_arr.include?(params[:id])
    @r = current_user.relationships.build
    @r.friend_id = params[:id]
    @r.save
   end
  end

follows_arr is an array of the IDs of the users the current user is following (current_user.relationships.map{|u| u[:friend_id]} ). params[:id] is the ID of the person the user is trying to follow.

For some reason, the second time someone clicks follow in this situation, the controller isn’t checking the updated database and two of the same ‘relationship’ are created.

Am I doing something wrong here? Is there another way to go about this?

Thanks!

Answer 1

The “real” answer to your problem is that those types of constraints should be checked in the model, not the controller (one may even argue it should be checked at database level, but Rails is just not made that way.

You can easily use the validates_uniqueness_of method in your model, e.g.:

class Relationship < ActiveRecord::Base
   belongs_to follower
   belongs_to followed_user

  validates_uniqueness_of :followed_user, :scope => :follower
end

Which would indicate that each that the followed_user must be unique per follower.

As for your original code, it is hard to say what is going wrong. It may depend on where the follows_arr comes from – maybe it contains some cached data, or you cached the variable yourself somewhere.

But while it will be a useful learning experience figuring out why the original solution doesn’t work, for solving your original problem you’ll be better of putting the code in the model where it belongs.

If you need to do something in the controller, you can check like this:

def follow
   ...
   if current_user.save
      # In this case everything was saved all right
   else
      # the user couldn't be saved for some reason (validation failed)
   end
 end