MongoDB lookup to various collections based on a field value - mongodb

Question

Consider there is documents like this in DB:
{
name: 'my list',
items: [
{ type: 'book', id: 5364 },
{ type: 'car', id: 354 },
{ type: 'laptop', id: 228 }
]
}
I need to grab data of each item from its own collection, based on type value.
I searched about it but couldn't figure out the correct approach.
Expected output:
{
name: 'my list',
items: [
{ type: 'book', id: 5364, data: [{...}] },
{ type: 'car', id: 354, data: [{...}] },
{ type: 'laptop', id: 228, data: [{...}] }
]
}
Mongoose schema of first collection (above):
{
name: String,
items: {
type: Array,
default: []
}
}
And other collections that must be looked up has corresponding _id field.

Answer 1

There are a few different ways to do this. To be most similar to what you have currently, you just need to make one small change. type is a keyword in Mongoose, so if you want to have a field in your schema which is actually called "type", you need to use the word twice. Once for the Mongoose keyword and again to define your schema.
{
name: String,
items: [{
type: { type: String},
id: Number,
data: []
}]
}
If the data field is coming from another collection, you could use a reference and then call populate() on your find method.
// ItemSchema
{
name: String,
items: [{
type: { type: String },
id: Number,
data: [{
type: Schema.Types.ObjectId,
ref: 'OtherSchemaName'
}]
}]
}
// Find Method with populate
const myList = await ItemSchema.find({type: "book"}).populate('data')
// Result
{
name: 'my list',
items: [
{ type: 'book', id: 5364, data: [{...}] },
]
}