Mapping in Storm swift?

Question

MongoDB

Good evening, there was such a problem: There is a main collection in which other collections are stored, to determine the collection of each of them, a unique id is assigned. Question: how to make mapping in storm (translation of the data that is in the database into an object) if this is not possible in storm, then advise which framework to use (without writing your own bicycles, of course)?

id				= this.data["_id"] as? String			?? ""
    firstname		= this.data["firstname"] as? String		?? ""
    lastname		= this.data["lastname"] as? String		?? ""
    email			= this.data["email"] as? String			?? ""
  }

This is how normal fields are mapped in storm, but how to implement this with collections, knowing only the id of the required collection from which you need to get data?