Relations in Prisma in NestJS - Mini Project: Build & Apply

Relations in Prisma with NestJS

📖 Scenario: You are building a simple blog backend using NestJS and Prisma. You want to model authors and their posts. Each author can have many posts, and each post belongs to one author.

🎯 Goal: Create Prisma models for Author and Post with a one-to-many relation. Then, write NestJS Prisma service code to fetch all posts with their authors.

📋 What You'll Learn

Create Prisma models Author and Post with a one-to-many relation

Add a config variable for Prisma client instance

Write a NestJS service method to fetch all posts including their author data

Complete the NestJS service class with Prisma client injection

💡 Why This Matters

🌍 Real World

Modeling and querying related data like users and their posts is common in web applications such as blogs, social media, and content management systems.

💼 Career

Understanding Prisma relations and integrating Prisma with NestJS is valuable for backend developers building scalable and maintainable APIs.

1

Define Prisma models for Author and Post

In your schema.prisma file, create two models: Author and Post. Define Author with fields id (Int, auto-increment, primary key) and name (String). Define Post with fields id (Int, auto-increment, primary key), title (String), and authorId (Int). Set up a one-to-many relation where Author has many posts and Post belongs to one author.

NestJS

// Define Prisma models Author and Post with one-to-many relation
// Your code here

Need a hint?

Remember to use @relation attribute on the Post model to link to Author.

2

Create Prisma client instance in NestJS service

In your NestJS service file, import PrismaClient from @prisma/client and create a constant called prisma that is a new instance of PrismaClient.

NestJS

model Author {
  id    Int    @id @default(autoincrement())
  name  String
  posts Post[]
}

model Post {
  id       Int    @id @default(autoincrement())
  title    String
  authorId Int
  author   Author @relation(fields: [authorId], references: [id])
}

import { PrismaClient } from '@prisma/client';
// Create Prisma client instance
// Your code here

Need a hint?

Use new PrismaClient() to create the client instance.

3

Write a method to fetch all posts with their authors

Inside your NestJS service class, write an async method called getAllPosts that returns all posts including their related author data. Use prisma.post.findMany with the include option to include author.

NestJS

model Author {
  id    Int    @id @default(autoincrement())
  name  String
  posts Post[]
}

model Post {
  id       Int    @id @default(autoincrement())
  title    String
  authorId Int
  author   Author @relation(fields: [authorId], references: [id])
}

import { PrismaClient } from '@prisma/client';

const prisma = new PrismaClient();

export class PostService {
  // Write async method getAllPosts to fetch posts with authors
  // Your code here
}

Need a hint?

Use include: { author: true } inside findMany to get author data.

4

Inject Prisma client into NestJS service class

Modify the PostService class to inject PrismaClient via the constructor. Add a private readonly property called prisma of type PrismaClient and assign it in the constructor parameter. Update the getAllPosts method to use this.prisma instead of the global prisma variable.

NestJS

model Author {
  id    Int    @id @default(autoincrement())
  name  String
  posts Post[]
}

model Post {
  id       Int    @id @default(autoincrement())
  title    String
  authorId Int
  author   Author @relation(fields: [authorId], references: [id])
}

import { PrismaClient } from '@prisma/client';

const prisma = new PrismaClient();

export class PostService {
  // Add constructor to inject PrismaClient
  // Update getAllPosts to use this.prisma
  // Your code here
}

Need a hint?

Use constructor injection to get PrismaClient instance and use this.prisma inside methods.