Rails - Apr 2006 - Problems with STI in has_many/belongs_to in Rails 1.1

I have a problem that surfaced in my attempt to upgrade my application  
to Rails 1.1.

We have a STI model on the "belongs_to" side of a has_many/belongs_to
relationship.  All my unit tests for this model pass, and the  
relationships all seem to work fine.

But in my functional tests, I''m getting errors.  I''ve traced
it back
into the call to the has_many association returning nil (To put it in  
familiar terms, this is like author.posts returning nil).  I was under  
the impression that a call to something like author.posts would NEVER  
return nil, you would just get an empty array.  In either case, it''s  
bad, because in my functional test, it should be getting at least one  
"post" back.

Does anyone have any insight here?  I''ve been banging my head against a
brick wall for a couple of days now, and I''m about ready to give up.

--
Lori Olson
http://blog.dragonsharp.com
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On Monday, April 03, 2006, at 5:06 AM, Lori Olson wrote:
>I have a problem that surfaced in my attempt to upgrade my application
>to Rails 1.1.
>
>We have a STI model on the "belongs_to" side of a
has_many/belongs_to
>relationship.  All my unit tests for this model pass, and the
>relationships all seem to work fine.
>
>But in my functional tests, I''m getting errors.  I''ve
traced it back
>into the call to the has_many association returning nil (To put it in
>familiar terms, this is like author.posts returning nil).  I was under
>the impression that a call to something like author.posts would NEVER
>return nil, you would just get an empty array.  In either case,
it''s
>bad, because in my functional test, it should be getting at least one
>"post" back.
>
Ok, I''ve narrowed this down to a regression in eager loading behavior.

Let me reframe the example a little.  Let''s say we have Author and
Topic
and Post.  Now, author has_many :topics, and topic has_many :posts.  To  
throw a wrench in the works, the Author also has a "current_topic" (So
they can logoff, and login, and start at the same place they left off),  
represented by current_topic_id in the authors table.

In Rails 1.1, when I go after author.current_topic.posts, I get nil.  In  
Rails 1.0, this works fine.

class Author
  has_many :topics
  belongs_to :current_topic, :class_name => "Topic", :foreign_key
=>
"current_topic_id"
end

class Topic
  has_many :posts
  has_one :current_for_author, :class => "Author", :foreign_key
=>
"current_topic_id"
end

class Post
  belongs_to :topic
end

I''ve tried using :include => :posts on the belongs_to
:current_topic,
but that really doesn''t work (the generated SQL is bizarre).  Any other
ideas are welcome.

Now that I understand it, I can work around it, but I think it qualifies  
as a bug...

--
Lori Olson
http://blog.dragonsharp.com

-- 
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On Monday, April 03, 2006, at 10:04 PM, Lori Olson
wrote:
>
>Ok, I''ve narrowed this down to a regression in eager loading
behavior.
>
>Let me reframe the example a little.  Let''s say we have Author and
Topic
>and Post.  Now, author has_many :topics, and topic has_many :posts.  To
>throw a wrench in the works, the Author also has a "current_topic"
(So
>they can logoff, and login, and start at the same place they left off),
>represented by current_topic_id in the authors table.
>
>In Rails 1.1, when I go after author.current_topic.posts, I get nil.  In
>Rails 1.0, this works fine.
>
>class Author
>  has_many :topics
>  belongs_to :current_topic, :class_name => "Topic",
:foreign_key =>
>"current_topic_id"
>end
>
>class Topic
>  has_many :posts
>  has_one :current_for_author, :class => "Author", :foreign_key
=>
>"current_topic_id"
>end
>
>class Post
>  belongs_to :topic
>end
>
>I''ve tried using :include => :posts on the belongs_to
:current_topic,
>but that really doesn''t work (the generated SQL is bizarre).  Any
other
>ideas are welcome.
>
>Now that I understand it, I can work around it, but I think it qualifies
>as a bug...
>
I guess I should also point out that in my case "Post" is an STI
class.

--
Lori Olson
http://blog.dragonsharp.com

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