Mongoose Methods not stored in Session? - express

Question

I'd like to use a Method defined in the Mongoose Model after saving the retrieved Object to a Session. Its not working though. Is it normal that these methods get lost after storing it to the session?
Calling Method from Mongoose Model works fine:
Puppies.findOne({_id:123}).then(puppy => puppy.bark()) // WOOF WOOF
Storing Model in Session and calling method fails:
// First Request
Puppies.findOne({_id:123}).then(puppy => {
req.session.puppy = puppy
})
// Second Request somewhere else in the app
app.use(function(req,res,next){
req.session.puppy.bark() // req.session.puppy.bark is not a function
})

Answer 1

I've got the exact issue, but I believe what happens is that when you're storing the variable in session, it's being toObject()'d, causing it to become a simple JavaScript object, instead of remaining as an instance of Model. I've used Model.hydrate as a means of recreating this Model instance.
app.use(function(req,res,next){
let puppyModel = mongoose.model("puppy");
let puppy = puppyModel.hydrate(req.session.puppy);
puppy.bark() // Awooo
});
This essentially is creating a new Model and then filling it with all the relevant information so it acts a clone.
Because it is needing all the relevant information to make an update (including _id if you have it), I believe you may need to extend the toObject function to return getters/virtuals:
puppySchema.set('toObject', { getters: true, virtuals: true });
Else, when it attempts to save, and it's missing the _id field, it won't be able to save it.
I do hope someone else can provide a nicer method of doing this and/or explain why when storing it it has to be converted to an object and can't remain as an instance of Model.

Answer 2

I think what Ciaran Blewitt said was correct. Finally worked around it by just using mongoose statics:
puppy.model.js
schema.statics.bark(puppy) {
console.log(puppy.sound)
}
Storing Model in Session and getting desired effect via static:
// First Request, storing Puppy in Session
Puppy.findOne({_id:123}).then(puppy => {
req.session.puppy = puppy
})
// Second Request somewhere else in the app
app.use(function(req,res,next){
Puppy.bark(req.session.puppy) // WOOF WOOF
})