Question

I’m using Rails’ accepts_nested_attributes_for method with great success, but how can I have it not create new records if a record already exists?

I have found this article, accepts_nested_attributes_for with find_or_create? but it doesn’t seem to work in my case.

I have a many-to-many relationship between packages and licenses. There should only be one instance of a license in the table, for instance: I shouldn’t have two licenses named, “Awesome”

The desired functionality is that when I create a package, passing in a license name as an attribute, create a new license if the name doesn’t already exist or create an association between the existing license (with the provided name) and the package.

Here are what my models look like:

class Package < ActiveRecord::Base
  has_and_belongs_to_many :licenses, :autosave => true
  accepts_nested_attributes_for :licenses
end

class License < ActiveRecord::Base
  attr_accessible :name
  has_and_belongs_to_many :packages
  validates :name, :presence => true
end

Answer 1

I had a similar issue and solved it with callback hooks. In my situation, I have a Status model and a Person model. I wanted to let users tag multiple people (Person) in their Status update by just typing in a names and it creating a new Person (these do no map to Users, btw, it’s just for private use) if a matching one does not exist.

class Person < ActiveRecord::Base
  has_and_belongs_to_many :statuses
end

Class Status < ActiveRecord::Base
  has_and_belongs_to_many :people
  accepts_nested_attributes_for :people
  before_save :get_people

  def get_people
    self.people.map! do |person|
      Person.find_or_create_by_name(person.name)
    end
  end
end