Custom return value for new / create ActiveRecord model

So I have a model (Photo), where when I call Photo.new @image => @image / Photo.create :image => @image, I want my model to find an existing photo with the same image hash OR create a new Photo from @image. Assume I can't use Photo.find_or_initialize_by_hash because I have a custom find function which finds close copies of images based on a soft image hash.

My first idea was to do

before_validation :check_duplicates, :on => :create

def check_duplicates
self = self.find_duplicate
end

Unfortunately, I realized you can't just redefine self in a model, so now I think the best approach is doing something along the lines of changing the return value from initialize to the duplicate.

Sort of like this, but it doesn't work (and I've heard horror stories about overriding initialize)

def initiali开发者_StackOverflowze(*params)
super(*params)
return self.find_duplicate || self
end

From what I gather your model structure looks something like this?

class Photo < ActiveRecord::Base
  has_one :image
end

class Image < ActiveRecord::Base
  belongs_to :photo
end

If so, you can simply do this:

class Photo < ActiveRecord::Base
  has_one :image, :uniq => true
end

Or if :image is just an attribute of Photo your first idea was on track:

class Photo < ActiveRecord::Base
  before_create :check_duplicate

  private
  def check_duplicate
    Photo.where(:image => self.image).count == 0 # will be false if Photo is found
  end
end

which will cancel the Photo from being created if #check_duplicate returns false (http://api.rubyonrails.org/classes/ActiveRecord/Callbacks.html)

Or simply

class Photo < ActiveRecord::Base
  validates_uniqueness_of :image
end