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Sequel Polymorphic
==================
A simple plugin for Sequel::Model's that lets you easily create polymorphic associations.
ActiveRecord Style
------------------
class Asset < ActiveRecord::Base
belongs_to :attachable, :polymorphic => true
end
class Post < ActiveRecord::Base
has_many :assets, :as => :attachable
end
class Note < ActiveRecord::Base
has_many :assets, :as => :attachable
end
@asset.attachable = @post
@asset.attachable = @note
In Sequel you would do the following:
class Asset < Sequel::Model
many_to_one :attachable, :reciprocal=>:assets, \
:dataset=>(proc do
klass = attachable_type.constantize
klass.filter(klass.primary_key=>attachable_id)
end), \
:eager_loader=>(proc do |key_hash, assets, associations|
id_map = {}
assets.each do |asset|
asset.associations[:attachable] = nil
((id_map[asset.attachable_type] ||= {})[asset.attachable_id] ||= []) << asset
end
id_map.each do |klass_name, id_map|
klass = klass_name.constantize
klass.filter(klass.primary_key=>id_map.keys).all do |attach|
id_map[attach.pk].each do |asset|
asset.associations[:attachable] = attach
end
end
end
end)
private
def _attachable=(attachable)
self[:attachable_id] = (attachable.pk if attachable)
self[:attachable_type] = (attachable.class.name if attachable)
end
end
class Post < Sequel::Model
one_to_many :assets, :key=>:attachable_id do |ds|
ds.filter(:attachable_type=>'Post')
end
private
def _add_asset(asset)
asset.attachable_id = pk
asset.attachable_type = 'Post'
asset.save
end
def _remove_asset(asset)
asset.attachable_id = nil
asset.attachable_type = nil
asset.save
end
def _remove_all_assets
Asset.filter(:attachable_id=>pk, :attachable_type=>'Post')\
.update(:attachable_id=>nil, :attachable_type=>nil)
end
end
class Note < Sequel::Model
one_to_many :assets, :key=>:attachable_id do |ds|
ds.filter(:attachable_type=>'Note')
end
private
def _add_asset(asset)
asset.attachable_id = pk
asset.attachable_type = 'Note'
asset.save
end
def _remove_asset(asset)
asset.attachable_id = nil
asset.attachable_type = nil
asset.save
end
def _remove_all_assets
Asset.filter(:attachable_id=>pk, :attachable_type=>'Note')\
.update(:attachable_id=>nil, :attachable_type=>nil)
end
end
@asset.attachable = @post
@asset.attachable = @note
Thats quite a bit of code. With sequel_polymorphic you can now do:
class Note < Sequel::Model
is :polymorphic
one_to_many :assets, :as => :attachable
end
class Asset < Sequel::Model
is :polymorphic
many_to_one :attachable, :polymorphic => true
end
voila!
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