Skip to main content

NestJS Multiple MongoDB Databases Accessing Sample Code


Most of the case's applications are going to communicate with more than one database. Here I'm going to walk through with sample NestJS application which communicates with multiple MongoDB's. Click here to know more about NestJS API CRUD using MongoDB.

MongoDB Atlas:

MongoDB Atlas is a cloud database. It has all the options of creating a MongoDB instance like for Free MongoDB Instance(for learning), Paid MongoDB Instance(for production). To illustrate multiple MongoDB connections for sample application here I'm going to use this Cloud MongoDB Atlas.

It is fairly minimal steps involved for created a Cloud MongoDB instance.
It is not mandatory to use the cloud based MongoDb database. You can use either locally installed instances like Mongo Shell, MongoDb Compass.

Create Sample NestJS Application:

NestJS provides CLI which helps to create a boilerplate templated application to getting started

NestJS CLI command:
npm i -g @nestjs/cli
Command to create NestJS sample application:
nest new your_application_name
Commands to start the application:
npm run Start:dev 
npm run Start:prod

mongoose and @nestj/mongoose:

mongoose and @nestjs/mongoose plugins used to create a communication bridge between MongoDB and NestJS application.
Commands to install:
npm install --save @nestjs/mongoose
npm install --save mongoose

Atlas MongoDB ConnectionString:

Now we need to fetch the connection string to configure in our NestJS application.
After clicking on the 'Connect your application' tab we can get connection string as below.

Configure  Multiple MongoDB:

Configure MongoDB connection as below.
import { MongooseModule } from '@nestjs/mongoose';
// some code hidden for display purpose
  imports: [
        connectionName: 'myWorldDb'
        connectionName: 'wildLifeDb'

export class AppModule {}
  • Import the MongooseModule from the '@nestjs/mongoose' library.
  • 'MongooseModule.forRoot' extension method takes the input parameters like database connection string and options object of type 'MongooseModuleOptions'.
  • 'MongooseModuleOptions' interface type has property like 'connectionName' which helps determine the kind of database connection for the specified connection string.
  • So on to configure multiple databases can be done by importing the multiple 'MongooseModule.forRoot' as above
  • In the sample above connection string, you need to use our own 'username' and 'password' while working with NestJS application with MongoDB
  • In the sample above 'MyWorld' and 'WildLife' pointed to the databases I have created in Cloud MongoDB Atlas.
Now to query the MongoDB collections(means Table), we need to configure the Mongo schema as follows.
src/schemas/myworld/student.schema.ts:(this schema represents 'MyWorld' database of collection name 'Student')
import * as mongoose from 'mongoose';
export const studentSchema = new mongoose.Schema({
    LastName: String,
    Standard: Number,
    FatherName: String,
    MotherName: String
  • 'mongoose' library gets imported into the variable name mongoose(import * as mongoose from 'mongoose')
  • Using the mongoose variable creating an instance of 'Schema' by registering all MongoDB Collection columns as property into it.
  • Now, this schema represents a Collection in MongoDB and using this schema we are able to query the collection.
Similarly, add the Schema of the Collection of another database as below:
src/schemas/wildlife/animal.schema.ts:(this scheme represents 'WildLife' database of collection name 'Animals'):
import * as mongoose from 'mongoose';

export const animalSchema = new mongoose.Schema({
Now register these Collection(Table) schemas in the application and also need to map them to appropriate database connections follows.
import { Module } from '@nestjs/common';
import { MongooseModule } from '@nestjs/mongoose';
import { studentSchema } from './schemas/myworld/student.schema';
import { animalSchema } from './schemas/wildlife/animal.schema';

  imports: [
        name: 'Student',
        schema: studentSchema,
        collection: 'Student',
        name: 'Animals',
        schema: animalSchema,
        collection: 'Animals'
        connectionName: 'myWorldDb'
        connectionName: 'wildLifeDb'

  controllers: [],
  providers: [],
export class AppModule {}
  • 'MongooseModule.forFeature()' extension method used to configure Collection(Table) schemas to their database respectively.
  • 'MongooseModule.forFeature()' extension expects 2 optional parameters. First optional parameter is array of type 'ModelDefinition'. Second optional parameter is 'connectionName' this connectionName must match with any one of the connectionName of the database configured in the application.
'ModelDefinition' type looks as below:
export declare type ModelDefinition = {
    name: string;
    schema: any;
    collection?: string;
  • 'name' property to specify the identity of 'ModelDefinition' in a collection of schema registration.
  • 'schema' property accepts the Collection(Table) Schema that we have created above.
  • 'Collection' property the value should match with MongoDB Collection name
Create models that represent the Collection(Table) in MongoDB. These models help to query the data against MongoDB using the registered schema. In NestJS these models can be created as 'Class' or 'Interface'
Models/myworld/student.model.ts:(represents 'Student' Collection(Table)):
export interface Student {
  FirstName: String;
  LastName: string;
  Standard: Number;
  FatherName: String;
  MotherName: String;
Models/wildlife/animal.model.ts:(represents 'Animals' Collection(Table)):
export interface Animal{

Create Service To Query MongoDB:

Services are injectable classes that are used to write logic to communicate with the databases.
import {Injectable} from '@nestjs/common';
import { InjectModel } from '@nestjs/mongoose';
import {Model} from 'mongoose';
import {Student} from '../Models/myworld/student.model';
import {Animal} from '../Models/wildlife/animal.model';

export class TestService{
        @InjectModel('Student') private readonly studentModel:Model<Student>,
        @InjectModel('Animals') private readonly animalModel:Model<Animal>){


    async getStudent(){
        return await this.studentModel.find();
    async getAnimals(){
        return await this.animalModel.find();
  • '@Injectable()' decorator makes class works with dependency injection. These classes can be accessed from the constructor. '@Injectable' imported from '@nestjs/common'.
  • '@InjectModel(Your_Schema_Registered_name)' this helps to inject the schema and helps in the query the MongoDB. '@InjectModel()' is imported from '@nestjs/mongoose'.
  • 'Model' from 'mongoose' helps to convert the schema to classes or interface.
  • 'find()' method used to query the MongoDB and you can pass some input value to fetch data conditionally. If no input parameter supplied to 'find()' method that means to fetch all data from the Collection(Table).
Now register the service in the app.module.ts file.
import {TestService} from './services/test.service';
// hidden code for display purpose
  providers: [TestService],
export class AppModule {}  

Test Results:

Now add a Test Controller as follows.
import { Controller,Get } from '@nestjs/common';
import { TestService } from '../services/test.service';

export class TestController{

    constructor(private testService:TestService){}

    async get(){
       return {
           Students: await this.testService.getStudent(),
           Animals: await this.testService.getAnimals()
Now register the TestController in the app.module.ts as below.
import {TestController} from './test/test.controller';
// code hidden for display purpose
  imports: [
  controllers: [TestController],
export class AppModule {}
Now run the application and call the test controller endpoint.

Wrapping Up:

Hopefully, this article will help to understand the accessing multiple MongoDB databases with NestJS application. I love to have your feedback, suggestions and better techniques in the comment section.

Follow Me:


  1. Great job there,

    What if I need to pass a dynamic dB Name to the connection.

    Such as

    I'll get the dBName from another dB and pass to this, from inside the controller.

    connectionName: 'wildLifeDb'

  2. Anyone knows how to do this but with Mongoose.forRootAsync ?


Post a Comment

Popular posts from this blog

.NET6 Web API CRUD Operation With Entity Framework Core

In this article, we are going to do a small demo on AspNetCore 6 Web API CRUD operations. What Is Web API: Web API is a framework for building HTTP services that can be accessed from any client like browser, mobile devices, desktop apps. In simple terminology API(Application Programming Interface) means an interface module that contains a programming function that can be requested via HTTP calls to save or fetch the data for their respective clients. Some of the key characteristics of API: Supports HTTP verbs like 'GET', 'POST', 'PUT', 'DELETE', etc. Supports default responses like 'XML' and 'JSON'. Also can define custom responses. Supports self-hosting or individual hosting, so that all different kinds of apps can consume it. Authentication and Authorization are easy to implement. The ideal platform to build REST full services. Create A .NET6 Web API Application: Let's create a .Net6 Web API sample application to accomplish our

Angular 14 Reactive Forms Example

In this article, we will explore the Angular(14) reactive forms with an example. Reactive Forms: Angular reactive forms support model-driven techniques to handle the form's input values. The reactive forms state is immutable, any form filed change creates a new state for the form. Reactive forms are built around observable streams, where form inputs and values are provided as streams of input values, which can be accessed synchronously. Some key notations that involve in reactive forms are like: FormControl - each input element in the form is 'FormControl'. The 'FormControl' tracks the value and validation status of form fields. FormGroup - Track the value and validate the state of the group of 'FormControl'. FormBuilder - Angular service which can be used to create the 'FormGroup' or FormControl instance quickly. Form Array - That can hold infinite form control, this helps to create dynamic forms. Create An Angular(14) Application: Let'

Part-1 Angular JWT Authentication Using HTTP Only Cookie[Angular V13]

In this article, we are going to implement a sample angular application authentication using HTTP only cookie that contains a JWT token. HTTP Only JWT Cookie: In a SPA(Single Page Application) Authentication JWT token either can be stored in browser 'LocalStorage' or in 'Cookie'. Storing JWT token inside of the cookie then the cookie should be HTTP Only. The HTTP-Only cookie nature is that it will be only accessible by the server application. Client apps like javascript-based apps can't access the HTTP-Only cookie. So if we use authentication with HTTP only JWT cookie then we no need to implement custom logic like adding authorization header or storing token data, etc at our client application. Because once the user authenticated cookie will be automatically sent to the server by the browser on every API call. Authentication API: To implement JWT cookie authentication we need to set up an API. For that, I had created a mock authentication API(Using the NestJS Se

Unit Testing Asp.NetCore Web API Using xUnit[.NET6]

In this article, we are going to write test cases to an Asp.NetCore Web API(.NET6) application using the xUnit. xUnit For .NET: The xUnit for .Net is a free, open-source, community-focused unit testing tool for .NET applications. By default .Net also provides a xUnit project template to implement test cases. Unit test cases build upon the 'AAA' formula that means 'Arrange', 'Act' and 'Assert' Arrange - Declaring variables, objects, instantiating mocks, etc. Act - Calling or invoking the method that needs to be tested. Assert - The assert ensures that code behaves as expected means yielding expected output. Create An API And Unit Test Projects: Let's create a .Net6 Web API and xUnit sample applications to accomplish our demo. We can use either Visual Studio 2022 or Visual Studio Code(using .NET CLI commands) to create any.Net6 application. For this demo, I'm using the 'Visual Studio Code'(using the .NET CLI command) editor. Create a fo

A Small Guide On NestJS Queues

NestJS Application Queues helps to deal with application scaling and performance challenges. When To Use Queues?: API request that mostly involves in time taking operations like CPU bound operation, doing them synchronously which will result in thread blocking. So to avoid these issues, it is an appropriate way to make the CPU-bound operation separate background job.  In nestjs one of the best solutions for these kinds of tasks is to implement the Queues. For queueing mechanism in the nestjs application most recommended library is '@nestjs/bull'(Bull is nodejs queue library). The 'Bull' depends on Redis cache for data storage like a job. So in this queueing technique, we will create services like 'Producer' and 'Consumer'. The 'Producer' is used to push our jobs into the Redis stores. The consumer will read those jobs(eg: CPU Bound Operations) and process them. So by using this queues technique user requests processed very fastly because actually

Angular 14 State Management CRUD Example With NgRx(14)

In this article, we are going to implement the Angular(14) state management CRUD example with NgRx(14) NgRx Store For State Management: In an angular application to share consistent data between multiple components, we use NgRx state management. Using NgRx state helps to avoid unwanted API calls, easy to maintain consistent data, etc. The main building blocks for the NgRx store are: Actions - NgRx actions represents event to trigger the reducers to save the data into the stores. Reducer - Reducer's pure function, which is used to create a new state on data change. Store - The store is the model or entity that holds the data. Selector - Selector to fetch the slices of data from the store to angular components. Effects - Effects deals with external network calls like API. The effect gets executed based the action performed Ngrx State Management flow: The angular component needs data for binding.  So angular component calls an action that is responsible for invoking the API call.  Aft

Usage Of CancellationToken In Asp.Net Core Applications

When To Use CancellationToken?: In a web application request abortion or orphan, requests are quite common. On users disconnected by network interruption or navigating between multiple pages before proper response or closing of the browser, tabs make the request aborted or orphan. An orphan request can't deliver a response to the client, but it will execute all steps(like database calls, HTTP calls, etc) at the server. Complete execution of an orphan request at the server might not be a problem generally if at all requests need to work on time taking a job at the server in those cases might be nice to terminate the execution immediately. So CancellationToken can be used to terminate a request execution at the server immediately once the request is aborted or orphan. Here we are going to see some sample code snippets about implementing a CancellationToken for Entity FrameworkCore, Dapper ORM, and HttpClient calls in Asp.NetCore MVC application. Note: The sample codes I will show in

Blazor WebAssembly Custom Authentication From Scratch

In this article, we are going to explore and implement custom authentication from the scratch. In this sample, we will use JWT authentication for user authentication. Main Building Blocks Of Blazor WebAssembly Authentication: The core concepts of blazor webassembly authentication are: AuthenticationStateProvider Service AuthorizeView Component Task<AuthenticationState> Cascading Property CascadingAuthenticationState Component AuthorizeRouteView Component AuthenticationStateProvider Service - this provider holds the authentication information about the login user. The 'GetAuthenticationStateAsync()' method in the Authentication state provider returns user AuthenticationState. The 'NotifyAuthenticationStateChaged()' to notify the latest user information within the components which using this AuthenticationStateProvider. AuthorizeView Component - displays different content depending on the user authorization state. This component uses the AuthenticationStateProvider

How Response Caching Works In Asp.Net Core

What Is Response Caching?: Response Caching means storing of response output and using stored response until it's under it's the expiration time. Response Caching approach cuts down some requests to the server and also reduces some workload on the server. Response Caching Headers: Response Caching carried out by the few Http based headers information between client and server. Main Response Caching Headers are like below Cache-Control Pragma Vary Cache-Control Header: Cache-Control header is the main header type for the response caching. Cache-Control will be decorated with the following directives. public - this directive indicates any cache may store the response. private - this directive allows to store response with respect to a single user and can't be stored with shared cache stores. max-age - this directive represents a time to hold a response in the cache. no-cache - this directive represents no storing of response and always fetch the fr

Angular 14 Crud Example

In this article, we will implement CRUD operation in the Angular 14 application. Angular: Angular is a framework that can be used to build a single-page application. Angular applications are built with components that make our code simple and clean. Angular components compose of 3 files like TypeScript File(*.ts), Html File(*.html), CSS File(*.cs) Components typescript file and HTML file support 2-way binding which means data flow is bi-directional Component typescript file listens for all HTML events from the HTML file. Create Angular(14) Application: Let's create an Angular(14) application to begin our sample. Make sure to install the Angular CLI tool into our local machine because it provides easy CLI commands to play with the angular application. Command To Install Angular CLI npm install -g @angular/cli Run the below command to create the angular application. Command To Create Angular Application ng new name_of_your_app Note: While creating the app, you will see a noti