By default, ActiveRecord’s polymorphic associations allow any type to be set. In practice, it is often only a subset of types that should actually be allowed in the association. This plugin adds an :allow option to the belongs_to class method, which will raise an ActiveRecord::AssociationTypeMismatch error if a non-allowed type is passed into the association. This is the same exception that is raised if you pass an object of the wrong type into a non-polymorphic association.
If a bogus class name is passed into the XXX_type= method for a polymorphic association, no exception is raised (certain validations will then cause a NameError to be raised, though). Since in a standard Rails use-case none of the application code will explicitly deal with that attribute value, there’s no DRY way to make sure that a legit class name is being passed in. With this plugin installed, the setter fails fast, raising an ActiveRecord::AssociationTypeNameError (this is a new one) if the class name does not exist. That way, your application can easily catch the error in a #rescue_action implementation.
$ sudo gem install outoftime-polymorphic_type_restrictions --source=http://gems.github.com
Then in your config/environment.rb
config.gem 'outoftime-polymorphic_type_restrictions', :lib => 'polymorphic_type_restrictions'
Just use the :allow key for belongs_to:
class Comment belongs_to :commentable, :polymorphic => true, :allow => %w(Commentable Photo) end
The allowed types can indicate a concrete class, a superclass, or an included module.
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Mat Brown <[email protected]>
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Adam Hooper <[email protected]>
Polymorphic Type Restrictions is released under the MIT License, copyright © 2009 Mat Brown.