Rails - Jul 2005 - Marking attributes as read-only in Active Record

In my models I represent some relations (views/tables) with attributes that
you are not allowed to insert or update. These constraints are enforced through
some triggers that set them to an automatically generated value that
is not to be
tampered with. To make this more clear to the users, these triggers throw
an exception when the user _does_ try to manually set such an attribute.

Active Record, however, doesn''t know about this and, on updates, tries
to
simply (re)set all fields.

Is there some way to make AR treat some given attributes as read-only?

 - Rowan

-- 
Morality is usually taught by the immoral.

On 5-jul-2005, at 20:59, BigSmoke wrote:
> In my models I represent some relations (views/tables) with  
> attributes that
> you are not allowed to insert or update. These constraints are  
> enforced through
> some triggers that set them to an automatically generated value that
> is not to be
> tampered with. To make this more clear to the users, these triggers  
> throw
> an exception when the user _does_ try to manually set such an  
> attribute.
>
> Active Record, however, doesn''t know about this and, on updates,  
> tries to
> simply (re)set all fields.
>
> Is there some way to make AR treat some given attributes as read-only?
I don''t think so, but you can stub them with accessors that throw

class Entity < ActiveRecord::base
    def temperature=(nt)
       raise "This attribute cannot be modified"
    end
end

AR will then try to use this accessor everytime the user tries to do  
an assignment (also when you do @entity[:temperature] = ''bla''
or
@entity.update_attributes(@params).

I am sure you can come up with some class method that will generate  
these pseude setters for you using class_eval.
-- 
Julian "Julik" Tarkhanov