Rails - Aug 2005 - Finding children in a model acting as a tree

In a model set to act as a tree, only the second of the functions
below works as expected. The first returns an empty array.  Why
does the id entry have to be fetched from the database for the
children function to work?  It''s slower and forces me to create
a root entry.  Thanks.

              def self.get_children( id )
                self.new( :id => id ).children
              end

              def self.get_children( id )
                find(id).children
              end

Mark Reginald James wrote:
> In a model set to act as a tree, only the second of the functions
> below works as expected. The first returns an empty array.  Why
> does the id entry have to be fetched from the database for the
> children function to work?  It''s slower and forces me to create
> a root entry.  Thanks.
> 
>              def self.get_children( id )
>                self.new( :id => id ).children
>              end
> 
>              def self.get_children( id )
>                find(id).children
>              end
I realise now that setting a foreign key attribute in a model
instance does not automatically instantiate its corresponding
table association attribute.  This is only done for instances
that come from the database.

To me this in non-intuitive.  Is it done for a reason?

-- 
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