fix_nested_attributes_for_uniqueness.rb

snippet.rb

def fix(records, params, matcher)
  params = params.deep_dup

  records.each do |record|
    if p.any? { |attrs| attrs['id'].present? && attrs['id'].to_i == record.id }
      next
    elsif (new_attrs = p.detect { |attrs| attrs['id'].blank? && attrs[matcher].present? && attrs[matcher].to_i == record[matcher] })
      new_attrs['id'] = record.id
    else
      p << { '_destroy' => true, 'id' => record.id }
    end
  end

  params
end