Mongoose populate: How to query multi-level document

#mongodb #mongoose #node #javascript

Sometimes you want to populate more than one level deep a schema using mongoose. i will share with you today how i use pure mongoose populate method to access more than one level deep data relation.

Suppose you have a User model that has many Posts and each post has Category.

Here we are going to retrieve a user with all posts that are not deleted with the category name and description populated.

Models

import * as mongoose from 'mongoose';
import { Schema } from 'mongoose';

// Category schema
export const categorySchema = new Schema({
    categoryName: {type: String, unique: true},
    description: {type: String},
    isDeleted: {type: Boolean, default: false}
}, {timestamps: true});

// Post schema
const postSchema = new Schema({
    title: { type: String },
    description: { type: String },
    category: { type: Schema.Types.ObjectId, ref: "Category"},
    isDeleted: { type: Boolean, default: false }
});

// User schema
const userSchema = new Schema({
    username: { type: String, unique: true },
    email: { type: String, unique: true },
    posts: [
     { type: Schema.Types.ObjectId, ref: "Post" }
    ]
});

export const Category = mongoose.model('Category', categorySchema);
export const Post = mongoose.model('Post', postSchema);
export const User = mongoose.model('User', userSchema);

Query

// Query to get all posts with the category 
const userWithPosts = await User.findById(id).populate({
   path: 'posts',
   model: Post,
   match: { isDeleted: false },
   populate: {
      path: 'category',
      model: Category,
      select: "categoryName description"
   }
}).exec();