ActiveRecord supports one-to-many polymorphic associations but not
many-to-many polymorphic associations. Thats what I wanted.
I emulate that behavior like this:
We have three models: - Article, Asset and Relationship
class Article < PolyRecord
habtm_polymorphs [:assets]
end
class Asset < PolyRecord
habtm_polymorphs [:articles]
end
class Relationship < ActiveRecord::Base
belongs_to :origin, :polymorphic => true
belongs_to :destination, :polymorphic => true
after_create :create_reverse_relationship
private
def create_reverse_relationship
rev = Relationship.new :origin => self.destination, :destination
=> self.origin
rev.save(false)
true
end
end
class PolyRecord < ActiveRecord::Base
self.abstract_class = true
def self.habtm_polymorphs(associations, options={})
associations = [associations].flatten
options[:polymorphic_join_table] ||= 'relationships'
options[:polymorphic_from] ||= 'origin'
options[:polymorphic_to] ||= 'destination'
pjoin = options[:polymorphic_join_table]
pto = options[:polymorphic_to]
pfrom = options[:polymorphic_from]
has_many pjoin, :as => pto
has_many pjoin, :as => pfrom
associations.each do |assoc|
has_many assoc, :through => pjoin, :source => pto, :source_type
=> assoc.to_s.singularize.camelize
end
after_destroy do |obj|
Relationship.delete_all({
:destination_id => obj.id,
:destination_type => obj.class.to_s
})
Relationship.delete_all({
:origin_id => obj.id,
:origin_type => obj.class.to_s
})
end
associations.each do |assoc|
define_method "#{assoc}=".to_sym do |args|
eval "self.#{assoc}.clear"
args = [args].flatten
Relationship.delete_all({
:origin_type => assoc.to_s.singularize.capitalize,
:destination_id => self.id,
:destination_type => self.class.to_s })
Relationship.destroy_all({
:origin_id => self.id,
:origin_type => self.class.to_s,
:destination_type => assoc.to_s.singularize.camelize })
eval "self.#{assoc} << args" unless args.empty?
end
end
end
end
Then you can use it like this:
@asset = Asset.new
@asset.articles = Article.first
@asset.articles = Article.all
@asset.articles << Article.new
@article.assets = @asset.articles.first.assets.last
On Feb 8, 11:18 pm, tsenart <[email protected]> wrote:
> Very cool! Thanks for the answer. But inverse associations are only a
> component of those double sided polymorphic associations.
> At the present you can only make one sided associations. Table talking
> it means the following:
>
> Single sided polymorphic:
> -----------------------------------------------
> | origin_id | destination_id | destination_type |
> -----------------------------------------------
>
> Double sided polymorphic:
> -------------------------------------------------------------
> | origin_id | origin_type | destination_id | destination_type |
> -------------------------------------------------------------
>
> This way there's only on table to track all these relations. It allows
> every model to be associated with every other model as many times as
> needed.
> For a better explanation I wrote something on Stackoverflow -> Here is
> the link
> again:http://stackoverflow.com/questions/2224994/why-are-double-sided-polym...
>
> On Feb 8, 10:12 pm, Mat Brown <[email protected]> wrote:
>
>
>
> > Inverse associations will be standard in Rails 2.3.6. For the
> > impatient, here's a backport:
>
> >http://github.com/oggy/inverse_of
>
> > Mat
>
> > On Mon, Feb 8, 2010 at 16:43, tsenart <[email protected]> wrote:
> > >http://stackoverflow.com/questions/2224994/why-are-double-sided-polym...
>
> > > --
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