MongoMapper: Override by setting ID

mongo_mapper_update_on_new.rb

require 'mongo_mapper'
MongoMapper.database = 'testing'

class SafeDoc
 include MongoMapper::Document
 key :name
 safe
end

puts "With a 'safe' document class:"

first_document = SafeDoc.create(:name => 'Raphael')
puts "Created doc: #{first_document.to_mongo.inspect}."

second_document = SafeDoc.create(:id => first_document.id, :name => 'John')
puts "Created doc: #{second_document.to_mongo.inspect}."
puts "First document is now: #{first_document.reload.to_mongo.inspect}."
#puts first_document.reload.name == 'John'
#This outputs true
puts
puts "With attr_accessible on 'name':" 
class ProtectedDoc
 include MongoMapper::Document
 key :name
 safe
 attr_accessible :name
end

first_document = ProtectedDoc.create(:name => 'Raphael')
puts "Created doc: #{first_document.to_mongo.inspect}."
second_document = ProtectedDoc.create(:id => first_document.id, :name => 'John')
puts "Created doc: #{second_document.to_mongo.inspect}."
puts "The create had no effect, but no error was raised, and second_document.persisted? is: #{second_document.persisted?}"
puts "First document is now: #{first_document.reload.to_mongo.inspect}."

#puts first_document.reload.name == 'John'
#This outputs false

#However:
puts "We have to use ProtectedDoc.new in order to expose this behavior."
third_document = ProtectedDoc.new(:name => 'John')
third_document.id = first_document.id
puts "With unsaved document: #{third_document.to_mongo.inspect}"
third_document.save
puts "After saving, the first document is: #{first_document.reload.to_mongo.inspect}."
#puts first_document.reload.name == 'John'
#This outputs true
#puts third_document.persisted?
#also true