Collection and Partials in Rails 3

Question

This my first time asking a question so please go easy one me :-p

I am following the examples on http://guides.rubyonrails.org/layouts_and_rendering.html#using-partials (Section 3.4.5 Rendering Collections) for rendering collections using partials. The code looks simple, but clearly I am missing something.

models/expert.rb contains the line:

attr_accessible :name

experts_controller.rb contains the following line in the index method:

@experts = Expert.all

views/experts/index.html.erb contains the following line:

<%= render :partial => "expert", :collection => @experts %>

views/experts/_expert.html.erb contains:

<%= expert.name %>

Upon viewing the index page in my browser I get the following error:

NoMethodError in Experts#index
undefined method `name' for nil:NilClass

I have been working on this for an hour and am completely stumped :-/ What little thing am I missing?

---Clarification---

Running '<%= debug @experts %>' within index.html.erb produces the following output:

- !ruby/object:Expert
attributes:
    id: 1
    name: Bob Smith
    slug: bob-smith
    created_at: '2012-03-11 18:37:11.791118'
    updated_at: '2012-03-11 18:55:58.179629'
  changed_attributes: {}
  previously_changed: {}
  attributes_cache: {}
  marked_for_destruction: false
  destroyed: false
  readonly: false
  new_record: false
- !ruby/object:Expert
  attributes:
    id: 2
    name: Steve Kamp
    slug: steve-kamp
    created_at: !!null 
    updated_at: !!null 
  changed_attributes: {}
  previously_changed: {}
  attributes_cache: {}
  marked_for_destruction: false
  destroyed: false
  readonly: false
  new_record: false

Does your Expert model actually have a name field? attr_accessible allows it to be assigned through mass assignment, but you must create the field in the schema (typically using a migration) in order for it to exist. — Jeremy Roman
@Jeremy Roman: Undefined method for nil class means he called #name on Nil. If @expert was not nil but there was no name attribute he would get NoMethodError — Andrew
Oh, I missed that it was on nil. My mind saw Expert again. (But it's NoMethodError in both cases.) — Jeremy Roman
@DannyDover: Ok, your error screen should show you a line number that the error is occuring on, can you paste the area around that line? Or, better yet, paste in the entire file where the error is occurring. — Andrew

Andrew Andrew · Accepted Answer · 2012-04-22T23:16:40

The exception almost certainly means that there are no experts, so @experts is an empty array. Have you created any expert records yet?

Also, just so you'll know, to render a collection of objects the way you're doing there's a nice shortcut:

render @experts

Collection and Partials in Rails 3

1 Answers