Rails - May 2011 - Will you please help me with a ActiveRelation that requires nested joins using scopes?

I am new to rails. Having a blast. The query API though is giving me
some trouble. I''ve been zooming and doing a lot of stuff very quickly,
but this is the first time I have spent hours trying to figure it out.
It''s not like anything I''ve used before - regular SQL, or
Hibernate,
or whatever.

The model I have is pretty simple.

A PrivateMessage has many Recipients
A Recipient has a Receiver (which of class User)
- recipient also has fields for ''is_read'' and
''is_deleted''

My goal is to build a query that finds all the unread and not deleted
private messages for a given user. To accomplish this, we need to join
''private_messages'' to ''recipients''... and
then ''recipients'' to
''users''.

My Recipient model has the following relevant code:

  belongs_to :receiver, :class_name => ''User'', :foreign_key
=>
"receiver_id"
  belongs_to :private_message

  scope :unread, where(:is_read => false).where(:is_deleted => false)
  scope :unread_by_receiver_id, lambda { |id|
unread.joins(:receiver).merge(User.by_id(id)) }

When tested in isolation, this works 100%.

However, when I code the private message queries, I run into problems.

  belongs_to :sender, :class_name => ''User''
  has_many :recipients, :class_name => ''Recipient''

  scope :sorted, order("private_messages.created_at desc")
  scope :newest, sorted.limit(3)
  scope :newest_unread_by_user_id, lambda {
      |id|
newest.joins(:recipients).merge(Recipient.unread_by_receiver_id(id)) }

When I try and use ''newest_unread_by_user_id, I get the following
exception:

    ActiveRecord::ConfigurationError: Association named ''user''
was not
found; perhaps you misspelled it?

This doesn''t make much sense to me... because if the name was spelled
wrong, why doesn''t it fail when I test it isolation?

Can someone help me out please? This one is driving me nuts. At times
like this, I just want to program in full sql and be done with it :(

Thanks

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Here''s the relevant User model code:

  has_many :sent_messages, :class_name => PrivateMessage, :foreign_key
=> ''sender_id''
  has_many :recipient_of_messages, :class_name =>
Recipient, :foreign_key => ''receiver_id''

  scope :by_id, lambda { |id| where(:id => id) }

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I also put this on stackoverflow if you want to get some points:
http://stackoverflow.com/questions/5865426/will-you-please-help-me-with-a-activerelation-that-requires-nested-joins-using-sc

It also looks better on there.

On May 3, 12:52 am, egervari
<ken.egerv...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> Here''s the relevant User model code:
>
>   has_many :sent_messages, :class_name => PrivateMessage, :foreign_key
> => ''sender_id''
>   has_many :recipient_of_messages, :class_name =>
> Recipient, :foreign_key => ''receiver_id''
>
>   scope :by_id, lambda { |id| where(:id => id) }
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