Question

I have a model that accepts nested params:

class Publication < ActiveRecord::Base
  attr_accessible :authors_attributes, :title

  has_many :authors
  accepts_nested_attributes_for :authors
end

In a before_create callback, I want to check if another Publication exists with the same title and authors. The callback would look something like this:

def find_duplicate
  Publication.where(self.instance_values["attributes"].except("id", "created_at",
    "updated_at")).each do |publication|
      if publication.author_names.sort == @authors
        return publication
      end
  end
end

The thing is, I have no idea how to get @authors. I’m assuming I can somehow retrieve the params in a similar fashion to self.instance_values["author_attributes"], but that’s turning up as nil. How else might I access the params?

Answer 1

You should have ‘authors’ as an accessor that’s built with the has_many. So, instead of @authors, you would simply use ‘authors’ or ‘self.authors’ to get the (non persisted) author objects that are about to be created. Try something like:

Publication.where(self.instance_values["attributes"].except("id", "created_at",
    "updated_at")).each do |publication|
      if publication.authors.collect{|a| a.name}.sort == self.authors.collect{|a| a.name}.sort
        return publication
      end
  end

There are likely better more efficient ways to compare author names here, but this is the clearest way to explain and keep with your paradigm.