Named scopes for instances

Question

I have following relationship schema:

class Participation
 belongs_to :toon
 belongs_to :person
 validates :role, :presence => true
end
class Toon
 has_many :participations
 has_many :people, :through => :participations
end
class Person
 has_many :participations
 has_many :toons, :through => :participations
end

I want to get people association related to toon, but filtered by role attribute value. I need something like toon.people_with_role('producer').

class Toon < ActiveRecord::Base
 has_many :participations
 has_many :people, :through => :participations
 def people_with_role(role)
 Participation.where(:toon_id => self, :role => role).map(&:person) 
 end
end

It works, but I'm not sure that it is a best way to do it.

Answer 1

Here is another way to filter people by role:

class Participation < ActiveRecord::Base
 belongs_to :toon
 belongs_to :person
 validates :role, :presence => true
end
class Person < ActiveRecord::Base
 has_many :participations
 has_many :toons, :through => :participations
end
class Toon < ActiveRecord::Base
 has_many :participations
 has_many :people, :through => :participations do
 def with_role(role)
 where('participations.role' => role)
 end
 end
end

Now, you can get the people fitered by role: toon.people.with_role('producer').

• Vladimir VG: Great, I don't knew that it can be done in that way.

Answer 2

I would create a scope under 'Person' for this, that way you can chain it together with other Person scopes. something like this should work (may have slight syntax errors).

scope :for_toon_with_role, lambda { |toon, role| joins(:participations).where(:participations => {:role => role, :toon_id => toon.id }) }

That way you can call it like this:

Person.for_toon_with_role(toon, 'role').all

Check out more info on rails scopes here:rails scopes