How to Create Repository in NestJS: Step-by-Step Guide

In NestJS, create a repository by defining an entity and then injecting the repository using @InjectRepository from @nestjs/typeorm. This repository allows you to perform database operations cleanly within your service classes.

Syntax

To create a repository in NestJS, you first define an entity class representing your database table. Then, inject the repository into your service using @InjectRepository(Entity). Use the repository methods to interact with the database.

• Entity: Defines the database table structure.
• @InjectRepository: Decorator to inject the repository.
• Repository: Provides methods like find, save, delete.

typescript

import { Entity, Column, PrimaryGeneratedColumn } from 'typeorm';
import { Injectable } from '@nestjs/common';
import { InjectRepository } from '@nestjs/typeorm';
import { Repository } from 'typeorm';

@Entity()
export class User {
  @PrimaryGeneratedColumn()
  id: number;

  @Column()
  name: string;
}

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

  findAll() {
    return this.userRepository.find();
  }
}

Example

This example shows how to create a User entity and a UserService that uses the repository to fetch all users from the database.

typescript

import { Module } from '@nestjs/common';
import { TypeOrmModule } from '@nestjs/typeorm';
import { Entity, Column, PrimaryGeneratedColumn } from 'typeorm';
import { Injectable } from '@nestjs/common';
import { InjectRepository } from '@nestjs/typeorm';
import { Repository } from 'typeorm';

@Entity()
export class User {
  @PrimaryGeneratedColumn()
  id: number;

  @Column()
  name: string;
}

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

  findAll() {
    return this.userRepository.find();
  }
}

@Module({
  imports: [TypeOrmModule.forFeature([User])],
  providers: [UserService],
  exports: [UserService],
})
export class UserModule {}

Output

When calling userService.findAll(), it returns a Promise resolving to an array of User objects from the database.

Common Pitfalls

Common mistakes when creating repositories in NestJS include:

• Not importing TypeOrmModule.forFeature([Entity]) in the module, so the repository is not registered.
• Forgetting to decorate the entity class with @Entity().
• Injecting the repository without @InjectRepository(Entity), which causes injection errors.
• Trying to use repository methods before the database connection is established.

typescript

/* Wrong: Missing TypeOrmModule.forFeature import */
@Module({
  providers: [UserService],
})
export class UserModule {}

/* Right: Include TypeOrmModule.forFeature */
import { TypeOrmModule } from '@nestjs/typeorm';

@Module({
  imports: [TypeOrmModule.forFeature([User])],
  providers: [UserService],
})
export class UserModule {}

Quick Reference

Step	Description
Define Entity	Create a class with @Entity() and columns.
Import Repository	Add TypeOrmModule.forFeature([Entity]) in module imports.
Inject Repository	Use @InjectRepository(Entity) in service constructor.
Use Repository	Call repository methods like find(), save(), delete().

Key Takeaways

Always decorate your entity class with @Entity() to define the database table.

Import TypeOrmModule.forFeature([Entity]) in your module to register the repository.

Inject the repository in your service using @InjectRepository(Entity) for database access.

Use repository methods like find() and save() to interact with the database.

Ensure your database connection is configured and established before using repositories.