ActiveRecord find_or_create methods

  def create
    company  = params[:person].delete(:company)
    @company = Company.find_or_create_by_name(company[:name])
    @person  = @company.people.create(params[:person])

    respond_to do |format|
      format.html { redirect_to(person_list_url) }
      format.js
      format.xml  { render :xml => @person.to_xml(:include => @company) }
    end
  end

Added find_or_initialize_by_X which works like find_or_create_by_X but doesn’t save the newly instantiated record. [Sam Stephenson]
Added constrain scoping for creates using a hash of attributes bound to the :creation key [DHH]. Example:

  Comment.constrain(:creation => { :post_id => 5 }) do
    # Associated with :post_id
    Comment.create :body => "Hello world"
  end

This is rarely used directly, but allows for find_or_create on associations. So you can do:

  # If the tag doesn't exist, a new one is created that's associated with the person
  person.tags.find_or_create_by_name("Summer")

Added extension capabilities to has_many and has_and_belongs_to_many proxies [DHH]. Example:

  class Account < ActiveRecord::Base
    has_many :people do
      def find_or_create_by_name(name)
        first_name, *last_name = name.split
        last_name = last_name.join " "

        find_or_create_by_first_name_and_last_name(first_name, last_name)
      end
    end
  end

  person = Account.find(:first).people.find_or_create_by_name("David Heinemeier Hansson")
  person.first_name # => "David"
  person.last_name  # => "Heinemeier Hansson"

Note that the anoymous module must be declared using brackets, not do/end (due to order of evaluation).