merge!

# File activerecord/lib/active_record/relation/spawn_methods.rb, line 41
    def merge!(other, *rest) # :nodoc:
      options = rest.extract_options!
      if other.is_a?(Hash)
        Relation::HashMerger.new(self, other, options[:rewhere]).merge
      elsif other.is_a?(Relation)
        Relation::Merger.new(self, other, options[:rewhere]).merge
      elsif other.respond_to?(:to_proc)
        instance_exec(&other)
      else
        raise ArgumentError, "#{other.inspect} is not an ActiveRecord::Relation"
      end
    end