Rails - Jan 2006 - setting default on "has_one" failure

Hi there,
I have a model for a Film, which:

  has_and_belongs_to_many :artists
  has_many                :stills
  has_one                 :preview_image,
                          :class_name => "Still", 
                          :conditions =>
"priority=''main''"

the has_one:preview_image and has_many:stills obviously draw from the same
table.

I was wondering if there is a way to set a default value for :preview_image (say
:stills[0] for example) if has_one fails to retrieve a :preview_image from the
db?

If it''s easier to send me link, then I''d happily read a page
about what you can do to models, as I''m finding it difficult to do very
much in the model pages.

thanks

dorian

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