Forum: Ruby on Rails an instance of one model in another model's definition?

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17fa7869b96bf7243280fe0c158b78d3?d=identicon&s=25 Michael Lascarides (mlas)
on 2006-04-05 17:33
Hi all,

I am creating a multiple-storefront shopping cart in Rails, and have run
into a small problem. In addition to the cart, line-item, product, and
order models (pretty much standard for this sort of thing), I have a
Storefront model which locates the current storefront (by examining the
domain name), and initializes itself. This works fine throughout, and by
declaring a "current_storefront" method in application.rb and
application_helper.rb, I have the current store's info available
throughout all controllers and views. OK so far.

However, I'd like to make some changes to the other models on the fly
depending on which storefront is loaded. For example, products have a
cross-sell relationship to themselves that varies by storefront. For
another example, order validations change from storefront to storefront
(i.e., "State" is not a required field in my UK store, but it is in my
US store).

The question I have, then, is how to load an instance of Storefront and
have that instance available in the other model definitions (order,
product, etc). It seems like there's probably an elegant Ruby idiom for
this I am missing. I'd interested to see how others solve this problem,
as it seems to be a pattern repeating in a few of my sites.

much thanks!

- michael.
C56f6508ce4610e8527606a435b5870f?d=identicon&s=25 William Lefevre (wlefevre)
on 2006-04-05 19:31
I'm pretty new at this so I'll be interested to see what the more
experienced people say but here's my two sense.

I'm assuming your model can't just reference the Storefront instance set
in your application controller because models don't talk to controllers
(controllers talk to models).

So one method is to have your controller explicitly pass your models a
reference to the Storefront.

    @cart.storefront = @storefront

But if you do this a lot then some type of a builder pattern might be
cleaner. Have your Storefront instantiate the models, give each model a
reference to itself, and return the model.

   @cart = @storefront.new_shopping_cart

inside Storefront

def new_shopping_cart
    cart = New Shopping_cart()
    cart.storefront = self
    cart
end

Note I am new at this so I quite easily could have made mistakes in the
actual code but hoepfull you get the idea.

- William
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