The search for #union

finding_union.rb

[6] pry(main)> left = User.where(name: "Bill")
  User Load (0.9ms)  SELECT "users".* FROM "users" WHERE "users"."name" = $1  [["name", "Bill"]]
=> []
[7] pry(main)> $ left.union
Error: Couldn't locate a definition for left.union!
[8] pry(main)> left.respond_to?(:union)
=> true
[9] pry(main)> $ left.method_missing

From: /Users/pdswan/code/scratch/rails4_union/rails4/vendor/bundle/ruby/2.0.0/gems/activerecord-4.2.0/lib/active_record/relation/delegation.rb @ line 91:
Owner: ActiveRecord::Delegation::ClassSpecificRelation
Visibility: protected
Number of lines: 11

def method_missing(method, *args, &block)
  if @klass.respond_to?(method)
    self.class.delegate_to_scoped_klass(method)
    scoping { @klass.public_send(method, *args, &block) }
  elsif arel.respond_to?(method)
    self.class.delegate method, :to => :arel
    arel.public_send(method, *args, &block)
  else
    super
  end
end