How to use update operators with save method?

I have successfully connected and can query for documents no problem. However, I have been searching around for how to use the update operators with the save method: http://docs.mongodb.org/manual/reference/operator/update/ I could not found how to use the update method directly with the ODM. Can somebody show me, for example, how to use $addToSet to add a value to an array of items in a document with Phalcon?

Same question. Is it possible in Phalcon