#1019 ✓not-applicable
Robert Sköld

"built in" to_yaml method gives anonymous class error

Reported by Robert Sköld | August 23rd, 2009 @ 01:53 PM

Running this simple model in TextMate and cmd-r:

require "rubygems"
require "dm-core"

class Test
  include DataMapper::Resource
  property :id,             Serial
  property :title,          String, :length => 1..255
  property :url,            String, :length => 1..255  


DataMapper::Logger.new(STDOUT, :debug)
DataMapper.setup(:default, ENV['DATABASE_URL'] || "sqlite3://#{Dir.pwd}/test.db")

Test.create( :title => "hello there" , :url => "http stuff" ).to_yaml

Throws this error:

TypeError: can't dump anonymous class Class

Ideally it should return a serialized yaml, something like this:

- !ruby/object: Test
     title: hello there
     url: http stuff

Comments and changes to this ticket

  • Martin Gamsjaeger (snusnu)

    Martin Gamsjaeger (snusnu) August 23rd, 2009 @ 02:55 PM

    • State changed from “new” to “confirmed”
    • Milestone set to 0.10.0
  • Martin Gamsjaeger (snusnu)

    Martin Gamsjaeger (snusnu) August 23rd, 2009 @ 02:56 PM

    If you add require "dm-serializer" it works as expected. Not sure if that should be required in this case though.

  • Martin Gamsjaeger (snusnu)

    Martin Gamsjaeger (snusnu) August 23rd, 2009 @ 02:59 PM


    I deleted the other duplicates. I'm not sure, I think you need privileges to be able to delete a ticket.

  • Robert Sköld

    Robert Sköld August 23rd, 2009 @ 03:29 PM

    Thanks Martin,

    I think what's expected would be the same as running to_yaml on a regular class?

    class TestClass
      attr_accessor :id, :title, :url
      def initialize( args )
        args.each { |key,val| instance_variable_set( "@#{key}" , val ) }
    p TestClass.new( :id => 1 , :title => "hello there", :url => "http stuff" ).to_yaml
    => "--- !ruby/object:TestClass \nid: 1\ntitle: hello there\nurl: http stuff\n"
  • JHStatewide

    JHStatewide September 30th, 2009 @ 06:05 PM

    Here's a temporary workaround, if you're really stuck (as I was). By no means is this a final solution but hopefully it will suffice until a real fix is posted.

    class Class

    def to_yaml( opts = {} )
       YAML.quick_emit(self.object_id, opts) do |out|
           out.map("!clazz") do |map|  


  • Dan Kubb (dkubb)

    Dan Kubb (dkubb) October 4th, 2009 @ 09:33 PM

    • Milestone changed from 0.10.0 to 0.10.2

    [project:id#20609 not-tagged:"0.10.0" milestone:id#51895 bulk edit command]

  • Dan Kubb (dkubb)

    Dan Kubb (dkubb) October 6th, 2009 @ 01:19 PM

    • Milestone cleared.
    • State changed from “confirmed” to “not-applicable”

    A DataMapper resource is not the same as a regular instance internally. We try hard to make it so the external representation of a Resource looks like a normal instance, but handling to_yaml without dm-serializer would require us to restructure it internally.

    YAML makes alot of assumptions about the internal structure of the objects that isn't always true, which is why we made the dm-serializer plugin that adds a proper to_yaml method to all resources.

    If you want to submit a patch that shows how YAML can be supported with minimal restructuring of Resource, I'll review and accept it if it's simple, otherwise my recommendation for this case is to use dm-serializer to get a proper Resource#to_yaml.

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