Social Networking with Rails using acts_as_network
Update 25-APR-2008: This plugin has been updated for Rails 2.0.
Update 06-JUN-2008: This plugin now includes acts_as_union, and we moved the repository to GitHub.
When we started integrating simple social networking features into PingMe we wanted to easily represent a bi-directional relationship between users in the system. When a user signs up for PingMe they can invite another user to join them. Once an invite is accepted, the users become mutual friends, or contacts in PingMe parlance, and can send Pings to each other.
Most importantly, we wanted the relationship to be bidirectional - when Jack is a friend of Jane then Jane should also be a friend of Jack.
Unfortunately we quickly realized that this model was not going to be so easy. The usual way of representing this type of network relationship using ActiveRecord is with an intermediate HABTM join, or with a self-referential has_many :through association. For example one might define a simple person model and then a join table to store the friendship relation:
create_table :people, :force => true do |t|
t.column :name, :string
end
create_table :friends, {:id => false} do |t|
t.column :person_id, :integer, :null => false
t.column :person_id_friend, :integer, :null => false # target of the relationship
end
The problem is that this model requires two rows in the intermediate table to make a relationship bi-directional.
jane = Person.create(:name => 'Jane') jack = Person.create(:name => 'Jack') jane.friends << jack jane.friends.include?(jack) => true # Jack is Janes friend jack.friends.include?(jane) => false # Jane is NOT Jack's friend
In short, you must explicitly define the reverse relation in order for this to work.
jack.friends << jane jack.friends.include?(jane) => true # now they're buds
This can be implemented in a fairly DRY way using association callbacks as
documented in Rails Recipes,
but things start to get ugly when you want to express the relationship through a
"proper" join model (like for an Invite) using has_many :through.
create_table :invites do |t|
t.column :person_id, :integer, :null => false # source of the relationship
t.column :person_id_friend, :integer, :null => false # target of the relationship
t.column :code, :string # random invitation code
t.column :message, :text # invitation message
t.column :is_accepted, :boolean
t.column :accepted_at, :timestamp # when did they accept?
end
In this case creating a reverse relationship is much more complex and could
require the duplication of multiple values, making the data model decidedly non-DRY.
Enter acts_as_network
acts_as_network is a plugin that we developed for PingMe to resolve some of these issues. It drives the social networking features of the site. It's intended to simplify the definition and storage of reciprocal relationships between entities using ActiveRecord by exposing a "network" of 2-way connections.
What makes it special is that it does this in a DRY way using only a
single record in an intermediate has_and_belongs_to_many join table or
has_many :through join model. There is no redundancy, and you need
only one instance of an association or join model to represent both directions
of the relationship. Consider this more desirable implementation:
class Invite < ActiveRecord::Base
belongs_to :person # the source of the invite
belongs_to :person_target, # the target of the invite
:class_name => 'Person',
:foreign_key => 'person_id_target'
end
class Person < ActiveRecord::Base
acts_as_network :friends, :through => :invites, :conditions => ["is_accepted = ?", true]
end
In this case acts_as_network implicitly defines five new properties on the Person model
person.invites_out # has_many invites originating from me to others
person.invites_in # has_many invites originating from others to me
person.friends_out # has_many friends :through outbound accepted invites from me to others
person.friends_in # has_many friends :through inbound accepted invites from others to me
person.friends # the union of the two friend sets - all people who I have
# invited all the people who have invited me and
Now...
# Jane invites Jack to be friends invite = Invite.create(:person => jane, :person_target => jack, :message => "let's be friends!") jane.friends.include?(jack) => false # Jack is not yet Jane's friend jack.friends.include?(jane) => false # Jane is not yet Jack's friend either invite.is_accepted = true # Now Jack accepts the invite invite.save and jane.reload and jack.reload jane.friends.include?(jack) => true # Jack is Janes friend now jack.friends.include?(jane) => true # Jane is also Jacks friend
So much cleaner!
Most of this magic is actually accomplished with a
UnionCollection class that provides useful application-space functionality
for emulating set unions across ActiveRecord collections. Once initialized,
the UnionCollection itself will act as an array containing all of the
records from each of its member sets, but its more interesting feature
is that it will intelligently forward ActiveRecord method calls like
find, find_all_by_*, etc. to its member sets.
Check it out
Further documentation is available online, and you can easily install acts_as_network as a plugin to try it out:
% script/plugin install git://github.com/sjlombardo/acts_as_network.git % rake doc:plugins
Please check it out and let us know what you think.
Saturday, May 10, 2008
Ismael says:
I was looking for something like this. Does it support eager loading with the :include option?
I'll check it out and thanks!
Saturday, May 10, 2008
Hans says:
You should be careful with [":conditions => "is_accepted = 't'"]. This will for example not work with a MySQL database.
Instead use [":conditions => "is_accepted = ?", true], which will let Rails autogenerate the correct true value for the current database.
Saturday, May 10, 2008
Stephen says:
@Hans - you're absolutely right - I've adjusted the example. Thanks!
Saturday, May 10, 2008
Ben says:
@Hans, thanks very much! Exactly what I was looking for.
Saturday, May 10, 2008
Vicent says:
Many thanks, this plugin is excelent.
Saturday, May 10, 2008
mmo says:
I know when creating a social network site how its important to track a users id and make sure they get credit when inviting others.
Thursday, June 05, 2008
millisami says:
I found the gem I was after for such a long time when I first started my project with ASP. Then later switched to PHP then Java, but still the mystery couldn't be resolved. Now at this stage, with RoR, I'm able to get a good picture of a social-networking site.
Thanks a lot.
Friday, July 11, 2008
reeze says:
what a plugin! just I want to find! thx a lot!
Monday, July 21, 2008
Eric says:
Where can we access the version for Rails 1.2? Thanks for your help.
Monday, July 21, 2008
Eric says:
Please disregard my comment above. Just migrated to Rails 2.1.0 to try your plugin. It's pretty cool! Thanks for all the hard work.
Monday, July 21, 2008
Eric says:
Please disregard my comment above. Just migrated to Rails 2.1.0 to try your plugin. It's pretty cool! Thanks for all the hard work.
Monday, February 22, 2010
Sites Internet says:
Hy,
I would like to know how to request the date of the invite after I request friend_in.
The ideal would be to have the date of invite in the user in the array of the friend_in. Because doing so, will only be need 1 mysql request