How use external entities in nestjs project with typeorm?

Using TypeORM in a NestJS project to handle external entities primarily involves several key steps, ensuring you can effectively integrate and use these entities regardless of whether they are defined within the same project or in an external library. Below, I will detail this process:

Step 1: Installation and Configuration of TypeORM

First, ensure your NestJS project has TypeORM installed. You can install it with the following command:

bash
npm install --save @nestjs/typeorm typeorm

Next, import TypeOrmModule in your app.module.ts or relevant module file:

typescript
import { Module } from '@nestjs/common';
import { TypeOrmModule } from '@nestjs/typeorm';

@Module({
  imports: [
    TypeOrmModule.forRoot({
      type: 'database type, e.g., postgres',
      host: 'localhost',
      port: 5432,
      username: 'user',
      password: 'password',
      database: 'db',
      autoLoadEntities: true,
      synchronize: true,
    }),
  ],
})
export class AppModule {}

Step 2: Importing External Entities

Assume you have an external npm package, such as my-external-models, which defines entities you want to use in your project. First, install this package:

bash
npm install my-external-models

Then, import these entities in any needed module and register them using TypeOrmModule.forFeature():

typescript
import { Module } from '@nestjs/common';
import { TypeOrmModule } from '@nestjs/typeorm';
import { ExternalEntity } from 'my-external-models';

@Module({
  imports: [
    TypeOrmModule.forFeature([ExternalEntity])
  ],
})
export class SomeModule {}

Step 3: Using Entities

Now, inject the repository for these entities in your service to perform database operations:

typescript
import { Injectable } from '@nestjs/common';
import { InjectRepository } from '@nestjs/typeorm';
import { Repository } from 'typeorm';
import { ExternalEntity } from 'my-external-models';

@Injectable()
export class SomeService {
  constructor(
    @InjectRepository(ExternalEntity)
    private externalEntityRepository: Repository<ExternalEntity>,
  ) {}

  async findAll(): Promise<ExternalEntity[]> {
    return await this.externalEntityRepository.find();
  }
}

Example: Handling Entities Defined Externally

Suppose you have an externally defined entity User, and you need to add a feature like finding a user by username. You can import and use this entity as shown above:

typescript
// User.service.ts
import { Injectable } from '@nestjs/common';
import { InjectRepository } from '@nestjs/typeorm';
import { User } from 'external-user-model';
import { Repository } from 'typeorm';

@Injectable()
export class UserService {
  constructor(
    @InjectRepository(User)
    private userRepository: Repository<User>,
  ) {}

  async findUserByUsername(username: string): Promise<User | undefined> {
    return this.userRepository.findOne({ where: { username } });
  }
}

This is a basic workflow enabling you to effectively integrate and use externally defined TypeORM entities within a NestJS project.