Mongoid ID issue with state_machine

Mongoid_id

# tl;dr if state_machine is in the model when a record is created, there is a record in Mongo, but you can't do a find() on it

# If state_machine is in the model when the record is created:

ruby-1.9.2-p0 > Upload.first.id
 => BSON::ObjectId('4db2a774c4054453d000000c') 

ruby-1.9.2-p0 > BSON::ObjectId.from_string('4db2a774c4054453d000000c')
 => BSON::ObjectId('4db2a774c4054453d000000c') 

ruby-1.9.2-p0 > Upload.first.id == BSON::ObjectId.from_string('4db2a774c4054453d000000c')
 => true 

ruby-1.9.2-p0 > Upload.find(BSON::ObjectId.from_string('4db2a774c4054453d000000c'))
Mongoid::Errors::DocumentNotFound: Document not found for class Upload with id(s) 4db2a774c4054453d000000c.
	from /Users/mtkd/.rvm/gems/ruby-1.9.2-p0/bundler/gems/mongoid-e1c8a436a70b/lib/mongoid/criterion/inclusion.rb:192:in `block in execute_or_raise'
	from /Users/mtkd/.rvm/gems/ruby-1.9.2-p0/bundler/gems/mongoid-e1c8a436a70b/lib/mongoid/criterion/inclusion.rb:190:in `tap'
	from /Users/mtkd/.rvm/gems/ruby-1.9.2-p0/bundler/gems/mongoid-e1c8a436a70b/lib/mongoid/criterion/inclusion.rb:190:in `execute_or_raise'
	from /Users/mtkd/.rvm/gems/ruby-1.9.2-p0/bundler/gems/mongoid-e1c8a436a70b/lib/mongoid/criterion/inclusion.rb:106:in `find'
	from /Users/mtkd/.rvm/gems/ruby-1.9.2-p0/bundler/gems/mongoid-e1c8a436a70b/lib/mongoid/finders.rb:67:in `find'
	from (irb):22
	from /Users/mtkd/.rvm/gems/ruby-1.9.2-p0/gems/railties-3.0.6/lib/rails/commands/console.rb:44:in `start'
	from /Users/mtkd/.rvm/gems/ruby-1.9.2-p0/gems/railties-3.0.6/lib/rails/commands/console.rb:8:in `start'
	from /Users/mtkd/.rvm/gems/ruby-1.9.2-p0/gems/railties-3.0.6/lib/rails/commands.rb:23:in `<top (required)>'
	from script/rails:6:in `require'
	from script/rails:6:in `<main>'


# if no state_machine is in the model when the record is created:

ruby-1.9.2-p0 > Upload.last.id
 => BSON::ObjectId('4db2a947c405445403000002') 

ruby-1.9.2-p0 > Upload.find('4db2a947c405445403000002')
 => #<Upload _id: 4db2a947c405445403000002, _type: nil, package_filename: "file.xml", attachable_id: nil, attachable_type: nil, created_at: 2011-04-23 10:26:15 UTC>


# the only difference is this code in the model:

state_machine :state, :initial => :empty do
end

Just happened to run across this gist. This issue occurs because defining a state called "empty" generates an instance method called "empty?". The ActiveSupport method "blank?" ends up being an alias for "empty?". It seems that Mongoid for some reason changes behavior depending on the return result of "blank?". You can fix this issue by changing the initial state to something different or adding a namespace to the state machine. You can reproduce this issue by removing state_machine from the equation and just adding the following instance method:

    def empty?
      true
    end

It would be nice to know why Mongoid relies on this method, but you should be able to work around it for now.

Awesome response - I was going to file it as a bug report but thought I was try to solve first.

Thanks.