But this is essentially allowing the type to be “any” object. I want the type to be an ObjectId of some document; it’s just that I want to be able to reference the id’s of documents from more than one model and therefore more than one collection (Student, Professor, and Administrator in this example). If I set the type to Schema.Types.Mixed, how will Mongo know which collection to query for the id that is stored there?
Or do you mean that instead of storing an ObjectId there, I would be storing an object that can have one of these three possible forms?
{ type: Schema.Types.ObjectId, ref: 'Student' }
{ type: Schema.Types.ObjectId, ref: 'Professor' }
{ type: Schema.Types.ObjectId, ref: 'Administrator' }
(If that is the case, then I guess the answer to my original question would be “no, it isn’t possible to have ‘ref’ refer to more than one data model at a time”.)