Rails - Jun 2009 - Order on virtual attribute in has_many

Hi all,

Consider the following models:
class Sheep < AR::B
  belongs_to :herd

  def some_virtual_attribute
    #returns something sortable
  end
end

class Herd < AR::B
  has_many :sheep do
    def some_method
      #do something useful
    end
  end
end

I want to be able to do:
  some_herd.sheep.some_method

But the collection sheep should be sorted on the
some_virtual_attribute of Sheep.

I tried something along the line of:
  has_many :sheep do
    def ordered
       sort {|a,b| a.some_virtual_attribute <=>
b.some_virtual_attribute}
    end
  end

This however returns an instance of Array on which the
''some_method''
is not defined. How can I solve this?

With kind regards,
Harm

To get this to work, you''d need to return an AssociationCollection,
which is going to be tricky. Association extensions aren''t *generally*
combinable like this; I think you may be thinking about named scopes.

--Matt Jones

On Jun 23, 11:58 am, harm
<harmaa...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> Hi all,
>
> Consider the following models:
> class Sheep < AR::B
>   belongs_to :herd
>
>   def some_virtual_attribute
>     #returns something sortable
>   end
> end
>
> class Herd < AR::B
>   has_many :sheep do
>     def some_method
>       #do something useful
>     end
>   end
> end
>
> I want to be able to do:
>   some_herd.sheep.some_method
>
> But the collection sheep should be sorted on the
> some_virtual_attribute of Sheep.
>
> I tried something along the line of:
>   has_many :sheep do
>     def ordered
>        sort {|a,b| a.some_virtual_attribute <=>
> b.some_virtual_attribute}
>     end
>   end
>
> This however returns an instance of Array on which the
''some_method''
> is not defined. How can I solve this?
>
> With kind regards,
> Harm