Executive summary: custom serialization does not convert objects to the storage type automatically and requires the object to be typecast manually instead

I used to have a field declared as "CompressedObject". With mongoid v2, this field defined two methods - serialize, which would gzip the content, and deserialize, which would unzip the content. When I switched to the new interface, I declared the new methods on the class and ran into a peculiar problem:

when I do model_instance.myfield = {:a => 1} and then model_instance.save, CompressedObject::mongoize is not called like before. Instead, mongoid looks for Hash::mongoize. Since the latter is missing, no compression gets done and the value is stored as is (at least according to the Moped logs showing the UPDATE/$set cmd going through). Next, when I try to recover the value by doing model_instance.myfield, this time around it is interpreted as a CompressedObject and the demongoize method is called. Of course, since my value is a plain hash, demongoize blows up.

By the way, when I try to assign and save {:b=>2}, this is what I get in the log (my field is called 'result'):

update={"$set"=>{"result"=>{:b=>2}

I am not yet sure if I can solve it on my end. Current behavior means that all my incoming hashes will be interpreted as Hash and unless I override serialization in the Hash class itself, they won't get compressed. Conversely, if I do provide mongoize/demongoize for Hash, then all Hash values will get compressed, even when I don't want that (e.g. when I declare a field as "Hash", rather than "CompressedObject").