On Tuesday 12 May 2009, Matt Jones wrote: > Haven't tried it, but have you considered switching the association > extension to a regular named_scope on Person? For simpler cases, I > know that the named_scope code is smart enough to use the scope > conditions to instantiate objects. Not sure if it will work here...
If I understand you correctly, I've already considered that case. class Person < ActiveRecord::Base named_scope :actors, ... # add a condition picking out the actors end Then, with movie.participants.actors I'd get the people who are participating in movie and who are actors. However, what I want are the people participating in movie *as* actors. It might be possible to get this to work as intended, but I tend to think it's not. Dealing with the joins involved is already tricky. ActiveRecord (almost) doesn't have an abstract model of queries, it more or less concatenates strings. There's no support for expressing, on the one hand, that a specific join is needed (without duplicating it), and on the other, that you want another, independent join. Michael > On May 11, 7:34 pm, Michael Schuerig <[email protected]> wrote: > > I have a model layer containing Movie, Person, Role, and RoleType, > > making it possible to express facts such as "Clint Easterbunny is > > director of the movie Gran Milano". > > > > The relevant model and associations look like this > > > > class Movie < ActiveRecord::Base > > has_many :roles, :include => :role_type, :dependent => :destroy > > > > has_many :participants, :through => :roles, :source => :person do > > def as(role_name) > > self.scoped( > > :joins => 'CROSS JOIN role_types', > > :conditions => [ > > "(roles.role_type_id = role_types.id) + > > " AND role_types.name = ?", > > role_name > > ] > > ) > > end > > end > > ... > > end > > > > Querying is easy: > > > > m = Movie.find_by_title('Gran Milano') > > m.participants.as('director') > > > > However, changing relations is painful. It's already bad with > > has_many > > > > :through associations when the intermediate model is not completely > > > > dumb, and my scope trickery doesn't make it any better. > > > > Now, let's assume for a moment that participants was a plain > > has_many association. Then it would be possible to write things > > like > > > > m.participants.clear > > m.participants << Person.find_by_name('Steve McKing') > > m.participant_ids = params[:movie][:participants] > > > > With the given has_many :through, none of these work, as Role > > object won't validate without a role type. Anyway, what I would > > like to write is > > > > m.participants.as('actor').clear > > m.participants.as('actor') << Person.find_by_name('Steve McKing') > > m.participants.as('actor') = > > Person.find(params[:movie][:participants]) > > > > I'm not sure this is possible with ActiveRecord as it is, but I'm > > looking forward to suggestions. > > > > Michael -- Michael Schuerig mailto:[email protected] http://www.schuerig.de/michael/ --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en -~----------~----~----~----~------~----~------~--~---
