NestjsHow-ToBeginner · 4 min read

How to Use Mongoose with NestJS: Simple Guide

To use mongoose with nestjs, install @nestjs/mongoose and mongoose, then import MongooseModule in your module with your schema. Use @InjectModel in your service to access the model and perform database operations.

📐

Syntax

Here is the basic syntax to integrate Mongoose in a NestJS module:

MongooseModule.forRoot('mongodb://localhost/dbname') connects to MongoDB.
MongooseModule.forFeature([{ name: 'Cat', schema: CatSchema }]) registers a schema.
@InjectModel('Cat') injects the model into a service.

typescript

import { Module } from '@nestjs/common';
import { MongooseModule } from '@nestjs/mongoose';
import { Cat, CatSchema } from './schemas/cat.schema';
import { CatsService } from './cats.service';

@Module({
  imports: [
    MongooseModule.forRoot('mongodb://localhost/nest'),
    MongooseModule.forFeature([{ name: Cat.name, schema: CatSchema }]),
  ],
  providers: [CatsService],
})
export class AppModule {}

💻

Example

This example shows a simple NestJS app using Mongoose to create and find cats in MongoDB.

typescript

import { Injectable } from '@nestjs/common';
import { InjectModel } from '@nestjs/mongoose';
import { Model } from 'mongoose';
import { Cat, CatDocument } from './schemas/cat.schema';

@Injectable()
export class CatsService {
  constructor(@InjectModel(Cat.name) private catModel: Model<CatDocument>) {}

  async create(name: string, age: number): Promise<Cat> {
    const newCat = new this.catModel({ name, age });
    return newCat.save();
  }

  async findAll(): Promise<Cat[]> {
    return this.catModel.find().exec();
  }
}

// cat.schema.ts
import { Prop, Schema, SchemaFactory } from '@nestjs/mongoose';
import { Document } from 'mongoose';

export type CatDocument = Cat & Document;

@Schema()
export class Cat {
  @Prop({ required: true })
  name: string;

  @Prop()
  age: number;
}

export const CatSchema = SchemaFactory.createForClass(Cat);

Output

When running, you can call CatsService.create('Tom', 3) to add a cat and CatsService.findAll() to get all cats.

⚠️

Common Pitfalls

Common mistakes include:

Not calling MongooseModule.forRoot() to connect to the database.
Forgetting to register schemas with MongooseModule.forFeature().
Injecting the model with the wrong name or missing @InjectModel().
Not awaiting async database calls.

typescript

/* Wrong: Missing forRoot connection */
@Module({
  imports: [
    MongooseModule.forFeature([{ name: Cat.name, schema: CatSchema }]),
  ],
})
export class AppModule {}

/* Right: Include forRoot with connection string */
@Module({
  imports: [
    MongooseModule.forRoot('mongodb://localhost/nest'),
    MongooseModule.forFeature([{ name: Cat.name, schema: CatSchema }]),
  ],
})
export class AppModule {}

📊

Quick Reference

Summary tips for using Mongoose with NestJS:

Install @nestjs/mongoose and mongoose packages.
Use MongooseModule.forRoot() once in the root module.
Register schemas with MongooseModule.forFeature() in feature modules.
Inject models with @InjectModel() in services.
Use async/await for database operations.

✅

Key Takeaways

Always connect to MongoDB using MongooseModule.forRoot() in your root module.

Inject models into services using @InjectModel() for database operations.

Use async/await to handle asynchronous Mongoose calls properly.

Double-check schema names and connection strings to avoid common errors.