How To Get Data From 2 Different Collections Of MongoDB Using Node.js?

Last Updated : 17 Oct, 2024

To retrieve data from two different collections in MongoDB using Node.js, we typically use the Mongoose library or the native MongoDB driver to establish a connection, query both collections and then combine or process the data as needed. This approach allows you to query multiple collections in parallel or in sequence, depending on your application’s requirements.

To get data from a collection with Mongoose in NodeJS you have to have two necessary things:

Schema: It is a document structure that contains the property with its types (default value, validations, etc. when required) as a key-value pair.
Model: It is a class created with the help of defined Schema and a MongoDB document is an instance of Model. Therefore, it acts as an interface for the MongoDB database for creating, reading, updating, and deleting a document.

After having a model, we can use the method find() on the model of a particular collection to get documents of the collection.

Syntax:

<Model_Name>.find(<query>,<projection>)

<query>: It is optional. It specifies a selection filter that is used to filter documents using various MongoDB query operators. If not passed, all the documents are returned.
<projection>: It is optional. It contains fields that we want to be returned to the documents that match the query filter. If not passed, all the fields are returned.

Steps To Get Data From 2 Different Collections Of MongoDB

Step 1: You can visit the link Install mongoose to install the Mongoose module. You can install this package by using this command.

npm install mongoose

Step 2: Now you can import the Mongoose module in your file using:

const mongoose = require('mongoose');

Step 3: Create a folder and add model.js and main.js files into it.

model.js: It contains schemas and models for all the collections you want to use, and then we are exporting all the models created so that they can be imported into the file in which we will get data from different collections.
main.js: It is the main server file here we will get data from two different collections.

JavaScript

//model.js  // Requiring module const mongoose = require('mongoose');  // Course Modal Schema const courseSchema = new mongoose.Schema({     _id: Number,     name: String,     category: String });  // Student Modal Schema const studentSchema = new mongoose.Schema({     name: String,     enroll: Number,     courseId: Number });  // Creating model objects const Course = mongoose.model('course', courseSchema); const Student = mongoose.model('student', studentSchema);  // Exporting our model objects module.exports = {     Student, Course }

Database: We already have documents in our Courses and Students collections from which we are going to get data as shown below:

mongoose-model — Get Data From 2 Different Collections Of MongoDB Using Node.js

Step 4: Database connection can be easily established using mongoose like:

mongoose.connect('mongodb://localhost:27017/GFG',
{  
    useNewUrlParser: true,  
    useUnifiedTopology: true,  
    useFindAndModify: false
});

Step 5: Write down the following code in the main.js file.

JavaScript

//main.js  const mongoose = require('mongoose');  // Importing Models Student and Course from model.js const { Student, Course } = require('./model');  // Connecting to database mongoose.connect('mongodb://localhost:27017/GFG',     {         useNewUrlParser: true,         useUnifiedTopology: true,         useFindAndModify: false     });  var dbcourse = [];  // Finding courses of category Database Course.find({ category: "Database" })     .then(data => {         console.log("Database Courses:")         console.log(data);          // Putting all course id's in dbcourse array         data.map((d, k) => {             dbcourse.push(d._id);         })          Student.find({ courseId: { $in: dbcourse } })             .then(data => {                 console.log("Students in Database Courses:")                 console.log(data);             })             .catch(error => {                 console.log(error);             })     })     .catch(error => {         console.log(error);     })

Run main.js file using the below command:

node main.js

Explanation: In the above code, in the file main.js, we are getting all the documents of Course collection whose category is Database then storing _id of each course in dbcourse array then getting all the documents from the Student collection whose is enrolled in any course of category Database.

Output: We are getting data from two different collections Courses and Students in the console shown below:

data-from-different-collection — Get Data From 2 Different Collections Of MongoDB Using Node.js

How to drop collection in MongoDb using Node.js ?

localhost3000

Improve

Article Tags :

How To Get Data From 2 Different Collections Of MongoDB Using Node.js?

Steps To Get Data From 2 Different Collections Of MongoDB

Similar Reads