How does Query.prototype.getPopulatedPaths() works in Mongoose ?

The Query.prototype.getPopulatedPaths() function is used to get a list of paths to be populated by this query. An array of strings representing populated paths is passed as a parameter.

Syntax:

Query.prototype.getPopulatedPaths()

Parameters: This function has one array parameter which is an array of strings representing populated paths.
Return Value: This function returns Query Object.

Mongoose Installation:

npm install mongoose

After installing the mongoose module, you can check your mongoose version in command prompt using the command. 

npm mongoose --version

After that, you can just create a folder and add a file for example, index.js as shown below.

Database: The sample database used here is shown below: 

Example 1:

index.js

const mongoose = require('mongoose');

// Database connection
mongoose.connect('mongodb://127.0.0.1:27017/geeksforgeeks', {
    useNewUrlParser: true,
    useCreateIndex: true,
    useUnifiedTopology: true
});

// User model
const User = mongoose.model('User', {
    name: { type: String },
    age: { type: Number }
});

const query = User.find().populate({
    path: 'level2',
    populate: { path: 'level3' }
});

console.log("Populate:", query.getPopulatedPaths());

The project structure will look like this: 

Run index.js file using below command: 

node index.js

Output:

Populate: [ 'level2', 'level2.level3' ]

Example 2:

index.js

const express = require('express');
const mongoose = require('mongoose');
const app = express()

// Database connection
mongoose.connect('mongodb://127.0.0.1:27017/geeksforgeeks', {
    useNewUrlParser: true,
    useCreateIndex: true,
    useUnifiedTopology: true
});

// User model
const User = mongoose.model('User', {
    name: { type: String },
    age: { type: Number }
});

const query = User.find().populate({
    path: 'level2',
    populate: { path: 'level3' }
});

console.log("Populate:", query.getPopulatedPaths());

app.listen(3000, function(error ) {
    if(error) console.log(error)
    console.log("Server listening on PORT 3000")
});

The project structure will look like this: 

Run index.js file using below command: 

node index.js

Output:

Server listening on PORT 3000
Populate: [ 'level2', 'level2.level3' ]

Reference: https://mongoosejs.com/docs/api/query.html#query_Query-getPopulatedPaths