Rails - Virtual attribute in form helper

Question

I'm having an odd error with a virtual attribute in a form helper.

My model looks like this:

class Folder < ActiveRecord::Base
 ...
  # VIRTUAL ATTRIBUTES
  def parent_name
   self.parent.name
  end

  def parent_name=(name)
    self.parent = self.class.find_by_name(name)
  end
  ...
end

I'm using HAML and SimpleForm. When I use my form like this...

= simple_form_for [@collection, form], :html => { :class => 'full' } do |f|
  = f.input :name
  = f.input :description
  = f.submit

... it works perfectly. But if I try to access the virtual attribute like so...

= simple_form_for [@collection, form], :html => { :class => 'full' } do |f|
  = f.input :name
  = f.input :parent_name
  = f.input :description
  = f.submit

... I get this error:

NoMethodError in Folders#index

Showing ... where line #3 raised:

undefined method `name' for nil:NilClass

Extracted source (around line #3):

1: = simple_form_for [@collection, form], :html => { :class => 'full' } do |f|
2:  = f.input :name
3:  = f.input :parent_name
4:  = f.input :description
5:  = f.submit

Any suggestions?

score 5 · Accepted Answer · answered Mar 05 '11 at 00:09

5

Try this:

def parent_name
 self.parent.nil? ? nil : self.parent.name
end

Problem is, that the it tries to access the name of the "parent" which doesn't exist. So parent is at this point Nil object and you're trying to access the attribute "name" of a Nil object -> Fails

Edit: maybe it's more suitable to return an empty string like:

self.parent.nil? ? "" : self.parent.name

answered Mar 05 '11 at 00:09

sled

14,525
3
42
70

When the form is rendered, it will first try to retrieve the value, and that fails, because there is not parent yet. This is indeed the fix! – nathanvda Mar 05 '11 at 00:11

score 1 · Answer 2 · answered Mar 05 '11 at 00:01

1

It looks like that error message is saying that

self.parent

is returning nil inside

def parent_name

answered Mar 05 '11 at 00:01

patrickmcgraw

2,465
14
8

Rails - Virtual attribute in form helper

2 Answers2