test_mongo_mapper_update_attributes.rb

# This script demonstrates an issue with MongoMapper's #update_attributes!. 
# Should call $set, but instead, just overwrites the entire doc.
#
# Script outputs:
#
#   doc[:one] # => "uno"
#   doc[:two] # => nil

class Doc
  include MongoMapper::Document

  key :one, String
  key :two, String
end

doc = Doc.create!

Doc.collection.update({
  :_id => doc.id
}, {
  :$set => {
    :two => "dos"
  }
})

doc.update_attributes!(:one => "uno")

doc.reload

puts "doc[:one] # => #{doc.one.inspect}"
puts "doc[:two] # => #{doc.two.inspect}"