Immutable Attributes in Ruby On Rails

Chiel Wester ma 21 jun 10

Sometimes you want to have some attributes on models that can be changed only on creation or only on certain conditions.

Of course there is attr_protected (to prevent mass assignment) and attr_readonly, but with these methods it’s difficult to create the conditions we actually want to apply.

For these situations you can install the immutable_attributes gem. Simple set the following in your model:

class Relation < ActiveRecord::Base
  attr_immutable :name
end

The attribute will be readonly for all (in this case) relations.

When you want to apply the immutable function only on certain conditions, you can do the following:

class Relation < ActiveRecord::Base
  validates_immutable :name, :if => Proc.new{|relation| relation.is_active?}
end

This function works like a validation, so you will get an validation error when you try to change the specified attribute.

Gepost in hor |  0 reacties