NestJS — Enterprise Node.js

MongoDB with Mongoose

17 min Lesson 25 of 30

MongoDB with Mongoose

Not every application fits a relational database. MongoDB is a document database that stores flexible, JSON-like documents — a great fit for content, catalogs, and rapidly-evolving schemas. NestJS integrates it through Mongoose, the most popular MongoDB library for Node.js, via the @nestjs/mongoose package.

SQL vs document thinking

In MongoDB you store documents in collections (rather than rows in tables). Related data is often embedded inside a document instead of split across tables and joined — which can make reads faster but changes how you model data.

Connecting

// npm install @nestjs/mongoose mongoose

import { MongooseModule } from '@nestjs/mongoose';

@Module({
  imports: [
    MongooseModule.forRoot('mongodb://localhost/app'),
  ],
})
export class AppModule {}

Defining a schema

With @nestjs/mongoose you define schemas as classes using the @Schema() and @Prop() decorators — familiar after TypeORM entities:

import { Prop, Schema, SchemaFactory } from '@nestjs/mongoose';
import { HydratedDocument } from 'mongoose';

export type UserDocument = HydratedDocument<User>;

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

  @Prop({ required: true, unique: true })
  email: string;

  @Prop({ default: true })
  isActive: boolean;
}

export const UserSchema = SchemaFactory.createForClass(User);

Registering and injecting the model

// users.module.ts
MongooseModule.forFeature([{ name: User.name, schema: UserSchema }]);

// users.service.ts
import { InjectModel } from '@nestjs/mongoose';
import { Model } from 'mongoose';

@Injectable()
export class UsersService {
  constructor(@InjectModel(User.name) private userModel: Model<UserDocument>) {}

  async create(dto: CreateUserDto) {
    return new this.userModel(dto).save();
  }

  findAll() {
    return this.userModel.find().exec();
  }
}

The model is your gateway. A Mongoose Model provides find, findById, create, updateOne, deleteOne, and more — the document-database equivalent of a repository.

Schema design trade-offs

Embedding — store related data inside the parent document. Fast reads, but documents can grow large and duplicated data is harder to update.
Referencing — store an id and look it up separately (like a foreign key). Normalised, but needs an extra query (populate()).

Schema-less does not mean think-less. MongoDB's flexibility tempts teams to skip data modelling. Inconsistent document shapes become a maintenance nightmare. Use schemas (as above) and model your access patterns deliberately.

Choose the database for the data, not the hype. Relational stores excel at structured, highly-related data with strong consistency; document stores excel at flexible, denormalised, read-heavy data. NestJS supports both equally well behind the same module/service patterns.

Summary

MongoDB stores flexible documents in collections, integrated into NestJS via Mongoose and @nestjs/mongoose. Define schemas with @Schema()/@Prop(), register them with forFeature(), and inject a typed Model with @InjectModel() to query and persist. Model embedding vs referencing deliberately. This completes Phase 5 — you can now persist data with relational and document databases. Next: authentication and authorization.