May a model know about the "outside world"?

Rails
1

Hi all

Most of my models have the attribute creator_id which is a foreign key
to a member. Also many have the attribute owner_id, which is a foreign
key to a member, too.

When being created, both attributes (if available) should get the ID of
the currently logged in member.

To implement this, I could “just” send the currently logged in member’s
ID to the model:

@my_model = MyModel.new(params[:my_model])
@my_model.creator = logged_in_member
@my_model.owner = logged_in_member
@my_model.save

Another way would be to leave it to the model itself to take care of
this, because when creating a new instance of it always a member is
logged in, so the model could somehow get the logged_in_member itself.

But now, would this injure the MVC principle? As far is I know the model
should not know anything about the “outside world”, right?

Or would you suggest a wholy different approach?

Thanks for your opinion
Josh

2

How would the model know about the logged in user if you don’t specify?
The
model doesn’t have access to controller or session information.

A cleaner way would be:

logged_in_member.my_models.create(params[:my_model])

then in the MyModel#before_save:

if self.owner.nil?
self.owner = self.creator
end

Jason

3

There’s a way to hack rails to make this happen. It violates every MVC
convention known and is a horrible idea.

The best approach is to do what you suggested… set it in the
controller.

4

Thank you both for your anwers. :slight_smile:

5

On 10/19/07, Brian H. [email protected] wrote:

There’s a way to hack rails to make this happen. It violates every MVC
convention known and is a horrible idea.

Yikes!

I don’t think it’s such a horrible idea if implemented properly. I’m
successfully using a slightly modified version of Bruce P.’
ModelSecurity library quite successfully.

The very high-level idea is:

  • The User model (or its equivalent) has a “current” method that
    returns a User object representing the currently logged-in user. All
    model code that needs to know the current user accesses User.current

  • A before_filter in ApplicationController assigns User.current

  • Thread-local storage is used to hold the value, since globals aren’t
    thread-safe.