Decoupling Data Access with the Repository Pattern in TypeScript and Node.js

Implementing the Repository Pattern with TypeScript and Node.js

The repository pattern is a design pattern that abstracts data storage, allowing for the decoupling of data access logic from business logic. This leads to a more maintainable, flexible, and scalable codebase.

Benefits of the Repository Pattern

• Enforces the dependency inversion principle
• Allows for separate testing of business logic and data access logic
• Keeps code structured and organized
• Reduces code duplication and enhances maintainability

Implementing the Repository Pattern with TypeScript and Node.js

In this example, we’ll use the Nest framework and Objection.js, an ORM built on top of Knex. We’ll create a PostRepository that encapsulates data access logic for posts.

Step 1: Create a New Nest App

Create a new Nest app using the Nest CLI:
bash
npx @nestjs/cli new my-nest-app

Step 2: Set Up the Database

Install the required dependencies:
bash
npm install --save @nestjs/objection objection knex pg

Set up the database connection in app.module.ts:
“`typescript
import { Module } from ‘@nestjs/common’;
import { AppController } from ‘./app.controller’;
import { AppService } from ‘./app.service’;
import { ObjectionModule } from ‘@nestjs/objection’;
import { knexConfig } from ‘./knex.config’;

@Module({
imports: [
ObjectionModule.forRoot(knexConfig),
],
controllers: [AppController],
providers: [AppService],
})
export class AppModule {}
“`
Step 3: Create a Post Model and Migration

Create a post.model.ts file:
“`typescript
import { Model } from ‘objection’;

export class Post extends Model {
id: number;
title: string;
content: string;
}

Create a migration for the posts table:
typescript
import { Migration } from ‘@nestjs/objection’;

export class PostMigration implements Migration {
async up(knex: Knex): Promise {
await knex.schema.createTableIfNotExists(‘posts’, (table) => {
table.increments(‘id’).primary();
table.string(‘title’);
table.text(‘content’);
});
}

async down(knex: Knex): Promise {
await knex.schema.dropTableIfExists(‘posts’);
}
}
“`
Step 4: Implement the Repository Pattern

Create a post.repository.ts file:
“`typescript
import { Injectable } from ‘@nestjs/common’;
import { InjectRepository } from ‘@nestjs/objection’;
import { Post } from ‘./post.model’;

@Injectable()
export class PostRepository {
constructor(private readonly postModel: typeof Post) {}

async findAll(): Promise

async findOne(id: number): Promise {
return this.postModel.query().findById(id);
}

async create(post: Post): Promise {
return this.postModel.query().insert(post);
}

async update(id: number, post: Post): Promise {
return this.postModel.query().updateAndFetchById(id, post);
}

async delete(id: number): Promise {
await this.postModel.query().deleteById(id);
}
}
“`
Using the Repository

Inject the PostRepository into a service or controller:
“`typescript
import { Controller, Get } from ‘@nestjs/common’;
import { PostRepository } from ‘./post.repository’;

@Controller(‘posts’)
export class PostController {
constructor(private readonly postRepository: PostRepository) {}

@Get()
async findAll(): Promise