20

I'm currently working on a small social networking application and right now I'm trying to create a model that represents friendships between users. This is what I came up with so far:

class User < ActiveRecord::Base

  # ...
  has_many :friendships
  has_many :friends, :through => :friendships

end

class Friendship < ActiveRecord::Base
  belongs_to :user
  belongs_to :friend, :class_name => 'User'
end

My friendship model has a field confirmed as boolean which I'd like to use to define a friendship as pending or confirmed.

How can I access all pending request for a certain user? Can I somehow define this using Rails' scope method? Something like

current_user.friendships.requests # => [Friendship, Friendship, ...]

would be great.

How can I make this association bidirectional? Do I simply add another friendship once one has confirmed a friend request such that my friendship table would look similar to this:

| user_id | friend_id | confirmed |
-----------------------------------
| 1       | 2         | true      |
| 2       | 1         | true      |
t6d
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5 Answers5

31

To access all pending friendships you can use an association:

has_many :pending_friends,
         :through => :friendships,
         :source => :friend,
         :conditions => "confirmed = 0"  # assuming 0 means 'pending'

To make the friendship bidirectional, you may want to replace your boolean confirmed column with a string status column that has one of the following three values: 'pending', 'requested' and 'accepted' (optionally 'rejected'). This will help keep track of who made the friendship request.

When a friendship request is sent (say from Foo to Bar), you create two friendship records (encapsulated in a transaction): one requested and one pending to reflect resp. that Bar has a requested friendship from Foo and Foo has a pending friendship with Bar.

  def self.request(user, friend)
    unless user == friend or Friendship.exists?(user, friend)
      transaction do
        create(:user => user, :friend => friend, :status => 'pending')
        create(:user => friend, :friend => user, :status => 'requested')
      end
    end
  end

When the friendship is accepted (e.g. by Bar), both friendship records are set to accepted. 

  def self.accept(user, friend)
    transaction do
      accepted_at = Time.now
      accept_one_side(user, friend, accepted_at)
      accept_one_side(friend, user, accepted_at)
    end
  end

  def self.accept_one_side(user, friend, accepted_at)
    request = find_by_user_id_and_friend_id(user, friend)
    request.status = 'accepted'
    request.accepted_at = accepted_at
    request.save!
  end

This is largely covered in chapter 14 of the Railspace book by Michael Hartl and Aurelius Prochazka. Here's the source code which should help you refine your solution.

hdtv1104
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mbreining
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  • Just to say thanks, you have helped me with the same problem, but in PHP. =) +1 – jonathancardoso Aug 25 '11 at 18:25
  • Do you know which attributes should be accessible in the Friendship Model? I am assuming only the status attribute should be accessible. Am I correct? – pratski Mar 26 '13 at 11:46
  • hi @mbreining I came across your solution today, i don't know if there is actually a more powerful solution than this, but i think it's not a good idea to create two lines for a relationship between 2 users in the Friendships table, i post a new question here if you can help http://stackoverflow.com/questions/19339596/the-best-way-to-implement-a-friendship-model-in-rails thank you – medBouzid Oct 12 '13 at 22:08
12

The ultimate reference:

http://railscasts.com/episodes/163-self-referential-association

apneadiving
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3

A short answer is yes. Just make another friendship record to represent bidirectional association.

I wrote a gem called has_friendship for this kind of problem. All you need to do is drop in has_friendship in your model, and all the associations and methods will be taken care of.

Hope this helps!

mc9
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2

Read up on this tutorial illustrating a relationship model on Rails Tutorials. It should be exactly what you are looking for.

acconrad
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1

I recommend you the book RailsSpace: Building a Social Networking Website. It clearly explains how to implement a friendship model. Though it isnt extensible to other forms of relationship but is pretty applicable for your problem.

Adi
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  • Do you know which attributes should be accessible in the Friendship Model? I am assuming only the status attribute should be accessible. Am I correct? – pratski Mar 26 '13 at 13:35