Mongoose, virtuals and Schemas - node.js

Question

I'm developing a NodeJS (Typescript) with Mongoose and when I try to add a virtual to my schema in one of the ways Mongoose's documentation suggests, I get an error saying that the prop virtuals doesn't exist in type SchemaOptions. And a correct error, even though the documentation suggests to use it.
This is what I find in the docs:
// That can be done either by adding it to schema options:
const personSchema = new Schema({
name: {
first: String,
last: String
}
}, {
virtuals: { //--------> I get the error here
fullName: {
get() {
return this.name.first + ' ' + this.name.last;
}
}
}
});
This is what I was trying:
const mySchema = new Schema<MyInterface>(
{
someProp: { type: Types.ObjectId, required: true, ref: "some-collection" },
myList: { type: [listSchema], required: true, default: [] },
},
{
timestamps: true,
toJSON: { virtuals: true },
toObject: { virtuals: true },
virtuals: {
getByType: {
get: (type: string) => {
return this.myList.filter((item: Item) => item.type === type);
}
}
}
}
);
In the other hand, I can set my virtual this way:
mySchema.virtual("getByType").get((type: string) => {
return this.myList.filter((item: Item) => item.type === type);
});
I had to do a few workarounds to sort the issue about not resolving the this keyword, but so far I have no problem about it...
The problem is: I use findOne and then try to call my virtual get with my document, but I get a Type Error saying Property 'getByType' does not exist on type 'MyInterface & Document<any, any, MyInterface>'.
Looks like there is a mix of mistake on the documentation and a Typescript problem here.
What do you suggest?

Answer 1

Virtual is intended to be used by a Class. If you want to use it on an instance, use methods instead.
Virtual
mySchema.virtual("getByType").get((type: string) => {
return this.myList.filter((item: Item) => item.type === type);
});
// Usage
MySchema.getByType(type)
Methods
mySchema.methods.getByType = function (type, cb) {
return this.model('MySchema').find({
myList: { $elemMatch: { type } }, // Fill your logic here
}, cb)
};
// Usage
const instance = MySchema.findOne();
const result = instance.getByType(type);