Ruby serializable_hash removes ruby/object from YAML output

I use YAML as a convenient way to serialize data in a number of projects, most of which are written in Ruby and Rails

You generate the YAML representation with the .to_yaml method - really simple.

p = Paper.find(359)
puts p.to_yaml

But if the input is a ruby or rails object the output is prefixed with !ruby/object and that causes problems when you try and load that document in another script that does not know about this object

For example - here is an example of a Paper object from a Rails application.

--- !ruby/object:Paper
attributes:
  id: 359
  pmid: 7945531
  title: 'Pharmacokinetics of a new human monoclonal antibody against cytomegalovirus.
    Third communication: correspondence of the idiotype activity and virus neutralization
    activity of the new monoclonal antibody, regavirumab in rat serum and its pharmacokinetics'
[...]

If I try and read this file in a separate script I get this error because that script has no concept of a Paper object.

y = YAML.load_file('test.yml')
ArgumentError: undefined class/module Paper
from /Users/jones/.rbenv/versions/2.1.1/lib/ruby/gems/2.1.0/gems/psych-2.0.5/lib/psych/class_loader.rb:53:in `path2class'
from /Users/jones/.rbenv/versions/2.1.1/lib/ruby/gems/2.1.0/gems/psych-2.0.5/lib/psych/class_loader.rb:53:in `resolve'
from /Users/jones/.rbenv/versions/2.1.1/lib/ruby/gems/2.1.0/gems/psych-2.0.5/lib/psych/class_loader.rb:45:in `find'
[...]

The way to strip off the ruby/object 'header' is to use serializable_hash before to_yaml.

---
abstract: TI-23 consists of lyophilized regavirumab (monoclonal antibody C23, MCA
[...]
id: 359
pmid: 7945531
publication_date: 1994-07-01
title: 'Pharmacokinetics of a new human monoclonal antibody against cytomegalovirus.
  Third communication: correspondence of the idiotype activity and virus neutralization
  activity of the new monoclonal antibody, regavirumab in rat serum and its pharmacokinetics'

It looks like the keys in the yaml block are output in alphabetical order.

It's a simple fix but I had to hunt around to find it.

Rails 3 YAML parse error and RedCloth

I moved a Rails 3.0.5 application to a new server with ruby 1.9.2, under rbenv. It had been working fine before but now I got this:

$ rails server
/Users/jones/.rbenv/versions/1.9.2-p290/lib/ruby/1.9.1/psych.rb:148:in `parse': couldn't parse YAML at line 183 column 9 (Psych::SyntaxError)
from /Users/jones/.rbenv/versions/1.9.2-p290/lib/ruby/1.9.1/psych.rb:148:in `parse_stream'
from /Users/jones/.rbenv/versions/1.9.2-p290/lib/ruby/1.9.1/psych.rb:119:in `parse'
from /Users/jones/.rbenv/versions/1.9.2-p290/lib/ruby/1.9.1/psych.rb:106:in `load'
from /Users/jones/.rbenv/versions/1.9.2-p290/lib/ruby/gems/1.9.1/gems/RedCloth-4.2.2/lib/redcloth/formatters/latex.rb:6:in `<module:LATEX>'
from /Users/jones/.rbenv/versions/1.9.2-p290/lib/ruby/gems/1.9.1/gems/RedCloth-4.2.2/lib/redcloth/formatters/latex.rb:3:in `<top (required)>'
[...]


There are a lot of posts about this error on the web. Some recommend specifying the 'syck' Yaml engine in the boot.rb file or messing with your libyaml setup. This did not work for me.

The solution turned out to be simple. You can see from the error message that the error is coming from the RedCloth gem. Previously I had been using version 4.2.2 (look in Gemfile.lock) even though I had not explicitly set that version.

On the new system I had version 4.2.9 installed. When I set this explicitly in the Gemfile I could start up the server just fine, after running 'bundle install'.

gem 'RedCloth', '>= 4.2.9'