# Whats the right way to avoid this nil error

**URL:** <https://www.ruby-forum.com/t/whats-the-right-way-to-avoid-this-nil-error/117051>\
**Category:** Rails\
**Created:** [October 12, 2007, 1:07pm UTC](https://www.ruby-forum.com/t/whats-the-right-way-to-avoid-this-nil-error/117051 "2007-10-12T13:07:27Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![casper\_the\_ghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/58956e/32.png) [@casper\_the\_ghost](https://www.ruby-forum.com/u/casper_the_ghost)\
**Post date:** [October 12, 2007, 1:07pm UTC](https://www.ruby-forum.com/t/whats-the-right-way-to-avoid-this-nil-error/117051/1 "2007-10-12T13:07:27Z")

</div>

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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<div class="post-metadata">

**Author:** ![casper\_the\_ghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/58956e/32.png) [@casper\_the\_ghost](https://www.ruby-forum.com/u/casper_the_ghost)\
**Post date:** [October 12, 2007, 1:33pm UTC](https://www.ruby-forum.com/t/whats-the-right-way-to-avoid-this-nil-error/117051/2 "2007-10-12T13:33:45Z")

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On Oct 12, 2007, at 1:05 PM, removed\_email\_address@domain.invalid 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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<div class="post-metadata">

**Author:** ![casper\_the\_ghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/58956e/32.png) [@casper\_the\_ghost](https://www.ruby-forum.com/u/casper_the_ghost)\
**Post date:** [October 12, 2007, 2:03pm UTC](https://www.ruby-forum.com/t/whats-the-right-way-to-avoid-this-nil-error/117051/3 "2007-10-12T14:03:37Z")

</div>

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

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<div class="post-metadata">

**Author:** ![casper\_the\_ghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/58956e/32.png) [@casper\_the\_ghost](https://www.ruby-forum.com/u/casper_the_ghost)\
**Post date:** [October 12, 2007, 4:36pm UTC](https://www.ruby-forum.com/t/whats-the-right-way-to-avoid-this-nil-error/117051/4 "2007-10-12T16:36:07Z")

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On Oct 12, 2007, at 1:50 PM, removed\_email\_address@domain.invalid 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