Question

I’m setting up a Rails project for a client, and they want Users (a model) to be able to follow each other (as in Twitter). They also want to be able to keep track of when one user started following another.

Since I need to keep track of the creation date, I figured, a has_many X, :through => Y relation would be the way to go, so the Y will keep track of the date it was created.

I have my Follow model set up:

class Follow < ActiveRecord::Base
  attr_accessible :actor_id, :observer_id, :follower, :followee
  attr_readonly :actor_id, :observer_id, :follower, :followee

  belongs_to :follower, :class_name => 'User', :foreign_key => :observer_id
  belongs_to :followee, :class_name => 'User', :foreign_key => :actor_id

  validates_presence_of :follower, :followee
  validates_uniqueness_of :actor_id, :scope => :observer_id
end

The question is how do I set up the relations in the User model?

Ideally I’d like it to have the following:

• :follows would be the associated Follow objects where self is the follower (observer_id)
• :followed would be the associated Follow objects where self is the followee (actor_id)
• :following would be the associated User objects where self is the follower (observer_id)
• :followers would be the associated User objects where self is the followee (actor_id)

I’m not sure how to write the has_many :through parts, though? Should I be using :source => X or foreign_key => X? And which key (actor_id or observer_id) should I put in each?

Edit: I’m currently doing this

has_many :follows, :foreign_key => :observer_id
has_many :followed, :class_name => 'Follow', :foreign_key => :actor_id
has_many :following, :class_name => 'User', :through => :follows, :source => :followee, :uniq => true
has_many :followers, :class_name => 'User', :through => :follows, :source => :follower, :uniq => true

and it’s mostly working. All of them except :followers work fine, but user.followers is doing something weird. It seems like it’s checking whether user is followING someone, and if they are then user.followers returns an array containing only user; if they’re not, it returns an empty array.

Does anyone have any advice?

Answer 1

It looks like this is the correct format:

has_many :follows, :foreign_key => :observer_id
has_many :followed, :class_name => 'Follow', :foreign_key => :actor_id
has_many :following, :class_name => 'User', :through => :follows, :source => :followee, :uniq => true
has_many :followers, :class_name => 'User', :through => :followed, :source => :follower, :uniq => true

For Rails newbies, the :uniq => true is important (as I discovered while doing this) because it keeps has_many X, :through => Y relations from returning duplicates (that is, without it, you might get multiple distinct objects, each with their own object ID, all referring to the same record/row).