Is there a way to have three way habtm associations in rails / activerecord?
Often three (or more) way associations are needed for habtm associations. For instance a permission model with roles.
A particular area of functionality has many users which can access many areas.开发者_Go百科
The permissions on the area are setup via roles (habtm)
The user/roles association is also habtm
The permissions (read, write, delete, etc) are habtm towards roles.
How would that be best done with rails/activerecord?
I'm not sure if you are just using Role based user permissions as an example, or if that is actually your goal.
Nested habtm
relationships are easy in Rails, though I would highly recommend Nested has_many :through
, just set them up as you would imagine:
class Permission < ActiveRecord::Base
end
#this table must have permission_id and role_id
class PermissionAssignment < ActiveRecord::Base
belongs_to :permission
belongs_to :role
end
class Role < ActiveRecord::Base
has_many :users, :through => :role_assignments
has_many :permissions, :through => :permission_assignments
end
#this table must have user_id and role_id
class RoleAssignment < ActiveRecord::Base
belongs_to :role
belongs_to :user
end
class User < ActiveRecord::Base
has_many :roles, :through => :role_assignments
end
This question about rails and RBAC (role-based authentication control) has a bunch of useful samples that provide the answer to this question and also sample implementations of your example.
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