Rails, storing a custom class with MongoMapper: Cannot serialize object into BSON

Question

I am using MongoMapper 0.9.1 in Rails 3.0.9 and it throws the following error, when I try to save an object of a custom class into the DB:

BSON::InvalidDocument (Cannot serialize an object of class Signature into BSON.)

My application will enable users to sign documents and these signatures should be saved in a custom class. I simply declared the Signature-class before the Doc-class which is going to store it:

class Signature
   @value
   @date
   @user
   def self.to_mongo(value)
      value.to_a
   end
   def self.from_mongo(value)
      Signature.new(value || [])
   end
end

class Doc
   # ...

No matter if I comment out the to_mongo or from_mongo methods, it always throws the exception quoted above when I want to test it by calling it from the controller via

 doc = Doc.new {:signature => Signature.new}

I have no idea why it won't work in my case. If anyone of you has got an idea it would be awesome if you help me. Thank you very much in advance!

Kind regards, Sebastian

Answer 1

Your key needs to be explicitly declared as the Signature type:

class Doc
  include MongoMapper::Document
  key :signature, Signature
end