Typescript: How to represent populated document fields on newly-constructed documents

[ajwootto]

Do you want to request a feature or report a bug?
feature? or question

What is the current behavior?
When constructing a new document which has a foreign key field that could be populated, sometimes I will construct the document using the full foreign document rather than just _id. I would then like to use the fields from that "populated" document from the resulting document I've constructed. However, the type system thinks that field is just an "_id". The only way I know how to get the document in its "populated" form would be to go and query for it using the populate method, and provide the populated "paths" object there. I obviously don't want to go and re-fetch the document I've just made, so is there any way to define that this field is populated on creation?

If the current behavior is a bug, please provide the steps to reproduce.

import { Schema, model, connect, Types } from 'mongoose'

interface NestedChild {
    name: string
    _id: Types.ObjectId
}
const nestedChildSchema: Schema = new Schema({ name: String })

interface Parent {
    nestedChild: Types.ObjectId
    name?: string
}

const ParentModel = model<Parent>('Parent', new Schema({
    nestedChild: { type: Schema.Types.ObjectId, ref: 'NestedChild' },
    name: String
}))

const NestedChildModel = model<NestedChild>('NestedChild', nestedChildSchema)

async function run() {
    await connect('mongodb://localhost:27017/')
    const parent = new ParentModel({
        nestedChild: new NestedChildModel({ name: 'test' }),
        name: 'Parent'
    })

    await parent.save()

    // doesn't work, nestedChild is expected to be an object id
    console.log(parent.nestedChild.name)
}

run()

What is the expected behavior?
I would like there to be a way to specify the "paths" on model construction similarly to "populate" so that documents I'm creating for the first time can be represented properly.

What are the versions of Node.js, Mongoose and MongoDB you are using? Note that "latest" is not a version.
Mongoose 6.3.1

[github-actions]

This issue is stale because it has been open 14 days with no activity. Remove stale label or comment or this will be closed in 5 days

[ajwootto]

not stale

[ajwootto]

@vkarpov15 one issue I'm encountering with the $assertPopulated solution is that it always returns the "interface" representation of the document instance rather than the full document. This causes issues for me when trying to interact with a new document with populated fields, and then call .save()

import { Schema, model, connect, Types } from 'mongoose'

interface NestedChild {
    name: string
    _id: Types.ObjectId
}
const nestedChildSchema: Schema = new Schema({ name: String })

interface Parent {
    nestedChild: Types.ObjectId
    name?: string
}

const ParentModel = model<Parent>('Parent', new Schema({
    nestedChild: { type: Schema.Types.ObjectId, ref: 'NestedChild' },
    name: String
}))

const NestedChildModel = model<NestedChild>('NestedChild', nestedChildSchema)

async function run() {
    await connect('mongodb://localhost:27017/')
    const parent = (new ParentModel({
        nestedChild: new NestedChildModel({ name: 'test' }),
        name: 'Parent'
    })).$assertPopulated<{nestedChild: NestedChild}>('nestedChild')

    // works, assertPopulated makes sure `parent` has a nestedChild field correctly typed
    console.log(parent.nestedChild.name)

   // doesn't work, parent is no longer a Document 
    await parent.save()
}

run()

Should I open a new issue for this?

edit:

changing the definition from this:

$assertPopulated<Paths = {}>(paths: string | string[]): Omit<DocType, keyof Paths> & Paths;

to this:

$assertPopulated<Paths = {}>(paths: string | string[]): Omit<this, keyof Paths> & Paths;

appears to fix the problem for me

edit:
opened a new issue here:
#12234