Using NestJS and TypeORM to Select Join Fields in Node.js with PostgreSQL
Tags: node, postgres, join, nestjs
Published: 2023-08-21 10:04:23

In the world of software development, Node.js has gained immense popularity due to its powerful capabilities and extensive libraries. When it comes to building robust and scalable applications, selecting join fields is a common requirement. In this article, we will explore how to achieve this using NestJS, a progressive Node.js framework, and TypeORM, an ORM for TypeScript and JavaScript.

NestJS provides a solid foundation for building server-side applications by leveraging TypeScript's strong typing system and decorators. It allows developers to structure their code in a modular and organized manner, making it easier to manage and maintain large-scale projects.

TypeORM, on the other hand, simplifies database interactions by providing a set of powerful features and abstractions. It supports various databases, including PostgreSQL, which we will be using in this example.

Let's dive into the code and see how we can select join fields using NestJS and TypeORM. First, we need to define our entities and their relationships. For instance, let's consider a scenario where we have two entities: User and Role. A user can have multiple roles, and a role can be associated with multiple users.

 

    
            import { Entity, Column, PrimaryGeneratedColumn, ManyToMany, JoinTable } from 'typeorm';
            
            @Entity()
            export class User {
                @PrimaryGeneratedColumn()
                id: number;
                
                @Column()
                name: string;
                
                @ManyToMany(() => Role)
                @JoinTable()
                roles: Role[];
            }
            
            @Entity()
            export class Role {
                @PrimaryGeneratedColumn()
                id: number;
                
                @Column()
                name: string;
                
                @ManyToMany(() => User, user => user.roles)
            users: User[];
        }
    

 

Once we have defined our entities, we can use the repository pattern provided by TypeORM to query the database and select join fields. Let's say we want to fetch all users along with their roles. We can achieve this by using the `createQueryBuilder` method and specifying the join conditions.

 

    
            import { Injectable } from '@nestjs/common';
            import { InjectRepository } from '@nestjs/typeorm';
            import { Repository } from 'typeorm';
            import { User } from './user.entity';
            
            @Injectable()
            export class UserService {
                constructor(
                    @InjectRepository(User)
                    private userRepository: Repository<User>
                ) {}
                
                async findAllUsersWithRoles(): Promise<User[]> {
                    return await this.userRepository
                    .createQueryBuilder('user')
                    .leftJoinAndSelect('user.roles', 'role')
                    .getMany();
            }
        }
    

 

In the above code snippet, we inject the `User` repository into the `UserService` class using the `@InjectRepository` decorator. Then, we define a method `findAllUsersWithRoles` that utilizes the `createQueryBuilder` method to perform a left join with the `roles` table and fetch all users along with their roles.

And that's it! We have successfully used NestJS and TypeORM to select join fields in Node.js with PostgreSQL. By leveraging the power of decorators and abstractions provided by these libraries, we can build efficient and maintainable applications.

So next time you find yourself needing to select join fields in your Node.js application, give NestJS and TypeORM a try. They will make your development process smoother and your code more enjoyable to work with. Happy coding!

References:
-----------

*   NestJS: [https://nestjs.com/](https://nestjs.com/)
*   TypeORM: [https://typeorm.io/](https://typeorm.io/)
*   PostgreSQL: [https://www.postgresql.org/](https://www.postgresql.org/)