On Wednesday, July 20, 2011 7:04:09 AM UTC-6, Jedrin wrote: > > > I have done a little polymorphic associations stuff and have > refreshed my memory on it again. > What it seems like is that if I have a particular record and I want to > make it easy for many different parent records to associate with it > using has_one or has_many, that is fine. > > If I want a parent record to have multiple kinds of children through > one association, I don't see how to do that (except maybe with STI but > then they all have to share the same fields in one record). I figure > there must be some way to do this with a kind of intermediate join or > something, but I haven't seen any examples that I can recall ..
If I understand what you're saying then no, it isn't even possible using a join table. This is the quick example I tested with: # The following demonstrates that this DOES NOT work... class Region < ActiveRecord::Base # a.k.a the "parent" that wants to "own" several # different kinds of children through one relation (shapes) has_many :regions_shapes has_many :shapes, :through => :regions_shapes end class RegionsShape < ActiveRecord::Base # polymorphic join model belongs_to :region belongs_to :shape, :polymorphic => true end class Ellipse < ActiveRecord::Base # one of two types of "children" that can belong to a # Region (parent) through its "shapes" relation has_one :regions_shape, :as => :shape has_one :region, :through => :regions_shape end class Polygon < ActiveRecord::Base # the other of the two types of "children" has_one :regions_shape, :as => :shape has_one :region, :through => :regions_shape end All of the relationships work fine EXCEPT for the one you wanted, in this example Region#shapes. Trying to use it will raise: ActiveRecord::HasManyThroughAssociationPolymorphicError: Cannot have a has_many :through association 'Region#shapes' on the polymorphic object 'Shape#shape' I think you'd have to simply have several explicit relationships for each type that the parent can "have": class Region < ActiveRecord::Base has_many :ellipses has_many :polygons end class Polygon < ActiveRecord::Base belongs_to :region end class Ellipse < ActiveRecord::Base belongs_to :region end Then just create a "combining" method for each relation-like action that the various relation methods support. Since you aren't working with actual relation objects, you can't chain or further filter on the results though so.... def shapes polygons + ellipses # or something like that for an Array (not a relation) end I'm assuming this is because if #shapes *could* be/return a relation then said relation would really have to have the ability to map to _n_ seperate SQL select statements (one for each table that can possibly be a "child"). As such, further filtering/sorting/offset/limit operations on such a relation would be hard, not make sense, or be impossible. Anyone more knowledgeable know if I'm wrong here? -- You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group. To view this discussion on the web visit https://groups.google.com/d/msg/rubyonrails-talk/-/JEYaqOQGEvYJ. To post to this group, send email to rubyonrails-talk@googlegroups.com. To unsubscribe from this group, send email to rubyonrails-talk+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en.