MongoMapper on Edge Rails (3.0.pre)

temporary-patch-fix.rb

# MongoMapper::Document::InstanceMethods

  def to_model
    errors.instance_eval do
      def [](attribute)
        return [] if errors[attribute.to_sym].nil?
        errors[attribute.to_sym]
      end
    end
    self
  end

validatable-errors-fix.rb

# A possible solution is to define Validatable::Errors#[] in
# jnunemaker-validatable to always return an Array.

# Validatable::Errors

  def [](attribute)
    return [] if errors[attribute.to_sym].nil?
    errors[attribute.to_sym]
  end

# Another solution might be to set #[] to alias #raw instead of #on
# and make sure that #raw always returns an Array.

# Validatable::Errors

  def raw(attribute)
    return [] if errors[attribute.to_sym].nil?
    errors[attribute.to_sym]
  end
  
  alias [] raw

# At this point MongoMapper::Document#to_model can be defined to
# just return self and everything should be working in Rails 3.0.pre
# and ActionPack, etc.