Problems accessing relational objects

Rails
1

Hi. I am frustrated here. I cannot access the attributes of the
relational model. This should be straight forward and simple, I guess
that’s why it’s frustrating. Let’s start with the models:

Models

class Ad < ActiveRecord:Base
belongs_to :book

class Book < Inventory
has_one :ad

(i’ve also played with has_many, but same scenario)

Ads Controller

@ads = Ad.find_all_by_user_id session[:user] #grab all ads from current
user

View

<% @ads.each do |ad| %>
<%= ad.book.nil? %> (will say it’s false, but yet…)
<%= ad.book.attributes %> (will give the following error:
<% end %>

“You have a nil object when you didn’t expect it!
You might have expected an instance of ActiveRecord::Base.
The error occured while evaluating nil.attributes”

Can someone help?

And happy New Years Eve Everyone!

D

2

Dominic S. wrote:

<% @ads.each do |ad| %>
<%= ad.book.nil? %> (will say it’s false, but yet…)
<%= ad.book.attributes %> (will give the following error:
<% end %>

“You have a nil object when you didn’t expect it!
You might have expected an instance of ActiveRecord::Base.
The error occured while evaluating nil.attributes”

I would try looking at the objects with debug:
<%= debug ad %>
<%= debug ad.book %>

Dan M.

3

Yes, did that and all the objects are in fact in the @ads variable, yet
I cannot access them… :frowning:

Dan M. wrote:

Dominic S. wrote:

<% @ads.each do |ad| %>
<%= ad.book.nil? %> (will say it’s false, but yet…)
<%= ad.book.attributes %> (will give the following error:
<% end %>

“You have a nil object when you didn’t expect it!
You might have expected an instance of ActiveRecord::Base.
The error occured while evaluating nil.attributes”

I would try looking at the objects with debug:
<%= debug ad %>
<%= debug ad.book %>

Dan M.

4

Man, if this is the case, STI needs to be a lot more flexible. I couldnt
use STI with an acts_as_tree also : (
(why would I do that? for a more human readable code to access the
different node levels…)

i do have a hint that this is the case, and i will try taking out the
STI…

Thanks Joe and Dan

Joe Hartman wrote:

class Book < Inventory
has_one :ad

Dominic

Looks like you’re using STI? I’ve never done this with STI. No reason to
think it wouldn’t work though. You might start with a simpler example
not using STI - as in the Agile Web Dev book p. 231.

Also, try using script/console to test things. Very handy tool for
sussing this stuff out.

The table structure, model, and code all need to be in sync.

Good luck

Joe

5

class Book < Inventory
has_one :ad

Dominic

Looks like you’re using STI? I’ve never done this with STI. No reason to
think it wouldn’t work though. You might start with a simpler example
not using STI - as in the Agile Web Dev book p. 231.

Also, try using script/console to test things. Very handy tool for
sussing this stuff out.

The table structure, model, and code all need to be in sync.

Good luck

Joe

6

My bad, STI does work. I had deleted inventory that @ads was trying to
call, that’s why it returned nil. It’s not nil on all returned entries,
just a few…