I’m trying to define multiple polymorphic relations (has_many_polymorphs plugin) from a single parent to same children.

Note has many viewers
Note has many editors
Viewers could be either Users or Groups
Editors could be either Users or Groups
Permission is the association model with note_id, viewer_id, viewer_type, editor_id, editor_type fields

Everything works out as expect as long as I have only one has_many_polymorphs relation defined in Note model

class User < ActiveRecord::Base; end

class Group < ActiveRecord::Base; end

class Note < ActiveRecord::Base has_many_polymorphs :viewers, :through => :permissions, :from => [:users, :groups] end

class Permission < ActiveRecord::Base belongs_to :note belongs_to :viewer, :polymorphic => true end

Note.first.viewers << User.first # =>  [#<User id: 1, ….>]
Note.first.viewers << Group.first # =>  [#<User id: 1, ….>, #<Group …>]
Note.first.viewers.first # => #<User ….>
Note.first.viewers.second # => #<Group ….>

Now, problems start to appear when I add the second relation

class Note < ActiveRecord::Base has_many_polymorphs :viewers, :through => :permissions, :from => [:users, :groups] has_many_polymorphs :editors, :through => :permissions, :from => [:users, :groups] end

class Permission < ActiveRecord::Base belongs_to :note belongs_to :viewer, :polymorphic => true belongs_to :editor, :polymorphic => true end

Note.first.viewers << User.first # => [#<User id: ....>]

>>>>>>>>

Note.first.editors << User.first

NoMethodError: You have a nil object when you didn’t expect it!
The error occurred while evaluating nil.constantize
… vendor/plugins/has_many_polymorphs/lib/has_many_polymorphs/base.rb:18:in `instantiate’

—-

I’ve tried refining the definition of has_many_polymorphs but it didn’t work. Not even with an STI model for ViewPermission \< Permission, and EditPermission \< Permission.

Any thoughts / workarounds / issue pointers are appreciated.

Rails 2.3.0

Posted to:

• Stack Overflow (http://stackoverflow.com/questions/983225/multiple-hasmanypolymorphs-in-one-model)
• Github (issue)  (http://github.com/fauna/has_many_polymorphs/issues/#issue/3)