Rails - Oct 2007 - whats the right way to avoid this nil error..

I have an model Order and a model Customer. Each customer has_many
Orders. Each Order belongs_to a Customer.

If I create an order but don''t specify a Customer (for whatever
reason, maybe it''s unknown at the time).. I obviously can''t
access
@order.customer.name because I''ll get a nil error...

So what''s the right way to handle that? If the Customer is nil I just
want to see just that... The blank space in my collection_select
selected... If the customer is nil I''d like my list views to just put
a blank in there...

I know I can do

@order.customer ? @order.customer.name : nil

but I don''t want to do that 100000 times... I know there has to be an
easier way just not exactly what.

Thanks.


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On Oct 12, 2007, at 1:05 PM,
frankjmattia-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org wrote:
> @order.customer ? @order.customer.name : nil
If that''s exceptional I use instead what''s called
"optimistic" approach:

   @order.customer.name rescue nil
> but I don''t want to do that 100000 times... I know there has to be
an
> easier way just not exactly what.
If that value with those semantics is used so much it would be a good  
idea to add it to the model:

   class Order
     ...

     def for
       customer ? customer.name : nil
     end
   end

to be able to just say

   <%= @order.for %>

I don''t know whether "for" is the best name but you see the
idea.

-- fxn


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Gotcha. Adding a method to the model was how I thought I should be
doing it but I wasn''t sure if the model would know what
"customer"
was... I mean, I guess it has to becaues of the association but I''m a
still a little uncertain on the different scopes in ruby.

I think it''s coming together now for me though... I''m looking
into it
more and I think I was assuming that
def for
would actually do what
def self.for
does. Which I didnt want. I think I''m cleared up now...

Thanks.
- FJM

On Oct 12, 7:30 am, Xavier Noria
<f...-xlncskNFVEJBDgjK7y7TUQ@public.gmane.org>
wrote:
> On Oct 12, 2007, at 1:05 PM,
frankjmat...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org wrote:
>
> > @order.customer ? @order.customer.name : nil
>
> If that''s exceptional I use instead what''s called
"optimistic" approach:
>
>    @order.customer.name rescue nil
>
> > but I don''t want to do that 100000 times... I know there has
to be an
> > easier way just not exactly what.
>
> If that value with those semantics is used so much it would be a good  
> idea to add it to the model:
>
>    class Order
>      ...
>
>      def for
>        customer ? customer.name : nil
>      end
>    end
>
> to be able to just say
>
>    <%= @order.for %>
>
> I don''t know whether "for" is the best name but you see
the idea.
>
> -- fxn

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On Oct 12, 2007, at 1:50 PM,
frankjmattia-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org wrote:
> Gotcha. Adding a method to the model was how I thought I should be
> doing it but I wasn''t sure if the model would know what
"customer"
> was... I mean, I guess it has to becaues of the association but
I''m a
> still a little uncertain on the different scopes in ruby.
I see.

Yes, it is expected that orders know about their customers, and  
belongs_to is the succint idiom to declare that relationship.  
Furthermore, take into account that models in Rails are not just Ruby  
proxies to database tables. Tables store the core attributes of  
models, but in the application side you normally add methods to the  
ones provided by AR so that the model offers the complete needed  
interface for your application.
> I think it''s coming together now for me though... I''m
looking into it
> more and I think I was assuming that
> def for
> would actually do what
> def self.for
> does. Which I didnt want. I think I''m cleared up now...
def self.for defines a class methods, def for defines an instance  
method. Objects like @order respond to instance methods. You need to  
learn Ruby to program in Rails.

-- fxn


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