Mongoose Populate cant get this to work？ - node.js

Question

book.schema.js
const mongoose = require('mongoose')
const Schema = mongoose.Schema
const BookSchema = new Schema({
name: {
type: String,
required: true
}
})
module.exports = BookSchema
book.model.js
const mongoose = require('mongoose')
const BookSchema = require('../schema/book.schema')
const Book = mongoose.model('Book', BookSchema)
module.exports = Book
novel.schema.js
const mongoose = require('mongoose')
const Schema = mongoose.Schema
const NovelSchema = new Schema({
name: {
type: String,
required: true
},
type: {
type: Schema.Types.ObjectId,
ref: 'Book'
}
})
module.exports = NovelSchema
novel.model.js
const mongoose = require('mongoose')
const NovelSchema = require('../schema/novel.schema')
const Novel = mongoose.model('Novel', NovelSchema)
module.exports = Novel
query
// Mongoose Populate cant get this to work
// I am at a loss
Novel.findById('5b87310d41073743856a7c4a').populate({
path: 'books'
})
mongoose populate not working。
Please let me know what I am doing wrong or give me a simple explanation...Thank you...

Answer 1

You are right to use the populate for loading the subdocument, but you need to pass the name of the book field in the novel schema, in your case the name is type.
Here is the link to documentation with some examples: Mongoose Populate
And below is the more one solution to your problem:
let book = await new BookModel({name:"book test"}).save();
console.log('-----------BOOK ITEM-------------');
console.log(book);
let novel = await new NovelModel({name:"novel test",type:book._id}).save();
console.log('-----------NOVEL ITEM-------------');
console.log(novel);
let itemPopulated = await NovelModel.findById(novel._id)
.populate('type')
.then((result) => {
return result;
}).catch((err) => {
console.log(err);
});
console.log('-----------ITEM POPULATED-------------');
console.log(itemPopulated);
And the execution output:

Answer 2

The parameter on the function populate() is the path of the field you want to populate, and also when you use populate or any chained function in mongoose you have to use the exec() function in the ending, so the correct way to do it would be:
Novel.findById('5b87310d41073743856a7c4a').populate({
path: 'type'
}).exec()