whats the right way to avoid this nil error..

rubyonrails-talk
1

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.

2

@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

3

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

4

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