Using accepts_nested_attributes_for with rejects_if

I'm using paperclip to attach photos to one of my mode开发者_JS百科ls:

class User < ActiveRecord::Base
  has_many :photos
  accepts_nested_attributes_for :photos
end

class Photo < ActiveRecord::Base
  belongs_to :user
  has_attached_file :data
end

How can I use reject_if to ignore data fields to which files are not uploaded by users?

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Try:

accepts_nested_attributes_for :photos, :reject_if => proc { |attrs| attrs['data'].blank? }

That should effectively ignore any data fields which are left blank by the user.