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= acts_as_network
acts_as_network is intended to simplify the definition
and storage of reciprocal relationships between entities using
ActiveRecord, exposing a "network" of 2-way connections between
records. It does this in DRY way using only <b>a single record</b>
in a <tt>has_and_belongs_to_many</tt> join table or <tt>has_many :through</tt>
join model. Thus, there is no redundancy and you need only one instance of
an association or join model to represent both directions of the relationship.
This is especially useful for social networks where
a "friend" relationship in one direction implies the reverse
relationship (when Jack is a friend of Jane then Jane should also
be a friend of Jack).
{Zetetic LLC}[http://www.zetetic.net] extracted acts_as_network from
PingMe[http://www.gopingme.com] where it drives the social
networking features of the site.
== INSTALLATION (git on edge rails)
% cd rails_project_path
% ./script/plugin install git://github.com/sjlombardo/acts_as_network.git
% rake doc:plugins
== INSTALLATION (subversion, rails <= 2.0.2))
% cd rails_project_path
% script/plugin source http://actsasnetwork.rubyforge.org/svn/plugins
% script/plugin install acts_as_network
% rake doc:plugins
== GitHub
http://github.com/sjlombardo/acts_as_network/tree/master
= INTRODUCTION
The usual way of representing network relationships in a database is
to use an intermediate, often self-referential, join table (HABTM).
For example one might define a simple person type
create_table :people, :force => true do |t|
t.column :name, :string
end
and then a join table to store the friendship relation
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
Unfortunately 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 # Jack is Janes friend
jane.friends.include?(jack) => true
Clearly Jack is Jane's friend, yet Jane is *not* Jack's friend
jack.friends.include?(jane) => false
unless you need to explicitly define the reverse relation
jack.friends << jane
Of course, this isn't horrible, and can in fact be implemented
in a fairly DRY way using association callbacks. However, things get
more complicated when you consider disassociation (what to do when Jane
doesn't want to be friends with Jack any more), or the very common
case where you want to express the relationship through a more complicated
join model via <tt>has_many :through</tt>
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 painful, and depending on
validations might require the duplication of multiple values, making the
data model decidedly un-DRY.
== Using acts_as_network
Acts As Network DRYs things up by representing only a single record
in a <tt>has_and_belongs_to_many</tt> join table or <tt>has_many :through</tt>
join model. Thus, you only need one instance of an association or join model to
represent both directions of the relationship.
== With HABTM
For a HABTM style relationship, it's as simple as
class Person < ActiveRecord::Base
acts_as_network :friends, :join_table => :friends
end
In this case <tt>acts_as_network</tt> will expose three new properies
on the Person model
me.friends_out # friends where I have originated the friendship relationship
# target in another entry (people I consider friends)
me.friends_in # friends where a different entry has originated the freindship
# with me (people who consider me a friend)
me.friends # the union of the two sets, that is all people who I consider
# friends and all those who consider me a friend
Thus
jane = Person.create(:name => 'Jane')
jack = Person.create(:name => 'Jack')
jane.friends_out << jack # Jane adds Jack as a friend
jane.friends.include?(jack) => true # Jack is Janes friend
jack.friends.include?(jane) => true # Jane is also Jack's friend!
== With a join model
This may seem more natural when considering a join style with a proper Invite model. In this case
one person will "invite" another person to be friends.
class Invite < ActiveRecord::Base
belongs_to :person
belongs_to :person_target, :class_name => 'Person', :foreign_key => 'person_id_target' # the target of the friend relationship
validates_presence_of :person, :person_target
end
class Person < ActiveRecord::Base
acts_as_network :friends, :through => :invites, :conditions => "is_accepted = 't'"
end
In this case <tt>acts_as_network</tt> implicitly defines five new properies
on the Person model
person.invites_out # has_many invites originating from me to others
person.invites_in # has_many invites orginiating 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 and all the people who have invited me
Thus
jane = Person.create(:name => 'Jane')
jack = Person.create(:name => 'Jack')
# 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
For more details and specific options see Zetetic::Acts::Network::ClassMethods
The applications of this plugin to social network situations are fairly obvious,
but it should also be usable in the general case to represent inherant
bi-directional relationships between entities.
= TESTS
The plugin's unit tests are located in +test+ directory under
<tt>vendor/plugins/acts_as_network</tt>. Run:
[%] cd vendor/plugins/acts_as_network
[%] ruby test/network_test.rb
This will create a temporary sqlite3 database, a number of tables,
fixture data, and run the tests. You can delete the sqlite database
when you are done.
[%] rm acts_as_network.test.db
The test suite requires sqlite3.
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