Forum: Ruby on Rails Self-referential habtm with condition is broken

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Michael S. (Guest)
on 2007-01-03 16:40
(Received via mailing list)
Here's a simplistic model class.

  class Person < ActiveRecord::Base
    has_and_belongs_to_many :relatives,
      :class_name => 'Person', :join_table => 'relatives',
      :foreign_key => 'from_id', :association_foreign_key => 'to_id'

    has_and_belongs_to_many :brothers,
      :class_name => 'Person', :join_table => 'relatives',
      :foreign_key => 'from_id', :association_foreign_key => 'to_id',
      :conditions => "gender = 'm'"
    #                 ^ plain reference to column

    has_and_belongs_to_many :sisters,
      :class_name => 'Person', :join_table => 'relatives',
      :foreign_key => 'from_id', :association_foreign_key => 'to_id',
      :conditions => "sisters_people.gender = 'f'"
    #                 ^ qualified reference to column

  end

The noteworthy things about it are that its habtm associations are
self-referential and that two of them have conditions. Let's see how to
use this. Also, the brothers and sisters associations use different
ways to refer to the column on which their respective condition
depends.

Lets put this class through its paces.

  >> Person.find(:first, :include => :sisters)
  -> works
  >> Person.find(:first, :include => :brothers)
  -> exception; invalid SQL, reference to column 'gender' is ambiguous

  >> p = Person.find(:first)
  >> p.brothers.map(&:first_name)
  -> works
  >> p.sisters.map(&:first_name)
  -> exception; invalid SQL, no alias defined for sisters_people

I may be missing something, but from what it looks like, ActiveRecord
doesn't handle this case as it should.

Michael

--
Michael S.
mailto:removed_email_address@domain.invalid
http://www.schuerig.de/michael/
Ilan B. (Guest)
on 2007-01-03 17:35
Michael S. wrote:
> Here's a simplistic model class.
>
>   class Person < ActiveRecord::Base
>     has_and_belongs_to_many :relatives,
>       :class_name => 'Person', :join_table => 'relatives',
>       :foreign_key => 'from_id', :association_foreign_key => 'to_id'
>
>
> Michael
>

Could you please provide the schema that this code is running against.
As a guess, it looks as though gender is defined in both the People?
table and it's join  (Relatives?) which would lead to an ambiguous query
unless it was explicitly qualified as it was in the sister's case.

ilan
Kad K. (Guest)
on 2007-01-03 18:51
Michael S. wrote:

>
> The noteworthy things about it are that its habtm associations are
> self-referential and that two of them have conditions. Let's see how to
> use this. Also, the brothers and sisters associations use different
> ways to refer to the column on which their respective condition
> depends.

Hi Michael

that's exactly what I am trying to solve using a :through statement...
if you solve this problem, please let me know... I'll appreciate cloning
your definitions....

Yves

mailto:removed_email_address@domain.invalid
Michael S. (Guest)
on 2007-01-03 19:55
(Received via mailing list)
On Wednesday 03 January 2007 16:35, Ilan B. wrote:
> Michael S. wrote:
> > Here's a simplistic model class.
> >
> >   class Person < ActiveRecord::Base
> >     has_and_belongs_to_many :relatives,
> >
> >       :class_name => 'Person', :join_table => 'relatives',
> >       :foreign_key => 'from_id', :association_foreign_key =>
> >       : 'to_id'

> Could you please provide the schema that this code is running
> against. As a guess, it looks as though gender is defined in both the
> People? table and it's join  (Relatives?) which would lead to an
> ambiguous query unless it was explicitly qualified as it was in the
> sister's case.

ActiveRecord::Schema.define(:version => 10) do
  create_table "people", :force => true do |t|
    t.column "first_name", :string,  :limit => 40, :null => false
    t.column "last_name",  :string,  :limit => 40, :null => false
    t.column "gender",     :string,  :limit => 1,  :null =>   end

  create_table "relatives", :id => false, :force => true do |t|
    t.column "from_id", :integer, :null => false
    t.column "to_id",   :integer, :null => false
  end
end

In case it wasn't clear from my original message, the point I'm trying
to make is that apparently it is not possible to specify a condition on
a habtm association in such a way that both fetching the associated
objects and finding with the association :include'd are possible.

Michael

--
Michael S.
mailto:removed_email_address@domain.invalid
http://www.schuerig.de/michael/
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