Rails - Aug 2006 - How to override append method for related attribute?

I have a model that looks something like this:

class Person < ActiveRecord::Base
  has_many :tasks
  [...]
end

I''d like to override/overload the append (<<) method for the
tasks
relational attribute such that I can perform some error checking in
the context of a Person.tasks << task operation.   Is there any way to
do this?

I wish I could do this in the context of validation, but it appears
that appending a task instance to a list associated with a person
instance causes the model to be saved in the database even if doing
the operation would cause validation to fail.   i.e., person.valid?
will return false as one would expect, but the data will persist!

I''d love your input on this matter.

--Michael

Michael S. Fischer wrote:
> I have a model that looks something like this:
> 
> class Person < ActiveRecord::Base
>  has_many :tasks
>  [...]
> end
> 
> I''d like to override/overload the append (<<) method for the
tasks
> relational attribute such that I can perform some error checking in
> the context of a Person.tasks << task operation.   Is there any way
to
> do this?
> 
> I wish I could do this in the context of validation, but it appears
> that appending a task instance to a list associated with a person
> instance causes the model to be saved in the database even if doing
> the operation would cause validation to fail.   i.e., person.valid?
> will return false as one would expect, but the data will persist!
Invalid records will persist in the loaded collection array, but
will not be saved to the database.  Are you sure the invalid
object is getting saved to the DB?

-- 
We develop, watch us RoR, in numbers too big to ignore.

Michael S. Fischer wrote:
> I have a model that looks something like this:
> 
> class Person < ActiveRecord::Base
>   has_many :tasks
>   [...]
> end
> 
> I''d like to override/overload the append (<<) method for the
tasks
> relational attribute such that I can perform some error checking in
> the context of a Person.tasks << task operation.   Is there any way
to
> do this?
You can do that with an association extension:

  has_many :tasks do
    def <<(task)
      if task.should_be_appended
        concat(task)  # aliased to << in base association proxy
      else
        raise SomeException
      end
    end
  end
> I wish I could do this in the context of validation, but it appears
> that appending a task instance to a list associated with a person
> instance causes the model to be saved in the database even if doing
> the operation would cause validation to fail.   i.e., person.valid?
> will return false as one would expect, but the data will persist!
If the appended object fails validation then the << won''t
succeed. Can
you put the validation test in Task instead of in Person?

--
Josh Susser
http://blog.hasmanythrough.com

-- 
Posted via http://www.ruby-forum.com/.

On 8/5/06, Josh Susser <josh@hasmanythrough.com> wrote:
> > I''d like to override/overload the append (<<) method
for the tasks
> > relational attribute such that I can perform some error checking in
> > the context of a Person.tasks << task operation.   Is there any
way to
> > do this?
>
> You can do that with an association extension:
>
>   has_many :tasks do
>     def <<(task)
>       if task.should_be_appended
>         concat(task)  # aliased to << in base association proxy
>       else
>         raise SomeException
>       end
>     end
>   end
Sexy, thanks!
> > I wish I could do this in the context of validation, but it appears
> > that appending a task instance to a list associated with a person
> > instance causes the model to be saved in the database even if doing
> > the operation would cause validation to fail.   i.e., person.valid?
> > will return false as one would expect, but the data will persist!
>
> If the appended object fails validation then the << won''t
succeed. Can
> you put the validation test in Task instead of in Person?
Indeed, moving the test to Task did the trick.  Thanks!

--Michael