Prisma Client usage in NestJS - Mini Project: Build & Apply

Prisma Client usage in NestJS

📖 Scenario: You are building a simple NestJS service to manage a list of books in a database. You will use Prisma Client to interact with the database.

🎯 Goal: Create a NestJS service that uses Prisma Client to fetch all books from the database.

📋 What You'll Learn

Create a Prisma Client instance

Configure Prisma Client in the service

Write a method to fetch all books using Prisma Client

Export the service class properly

💡 Why This Matters

🌍 Real World

This project shows how to use Prisma Client in a NestJS backend to interact with a database, a common task in building APIs.

💼 Career

Understanding Prisma Client usage in NestJS is valuable for backend developers working with modern Node.js frameworks and databases.

1

Create Prisma Client instance

Import PrismaClient from @prisma/client and create a constant called prisma that is a new instance of PrismaClient.

NestJS

# Your code here

Hint

Use import { PrismaClient } from '@prisma/client' and then const prisma = new PrismaClient().

2

Create NestJS service class

Create a class called BooksService and add a constructor that assigns the prisma instance to a private readonly property called prisma.

NestJS

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

const prisma = new PrismaClient();

// Create BooksService class with constructor
# Your code here

Hint

Define class BooksService with a constructor() that sets this.prisma = prisma.

3

Add method to fetch all books

Inside the BooksService class, add an async method called getAllBooks that returns the result of this.prisma.book.findMany().

NestJS

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

const prisma = new PrismaClient();

export class BooksService {
  private readonly prisma: PrismaClient;

  constructor() {
    this.prisma = prisma;
  }

  // Add async getAllBooks method
  # Your code here
}

Hint

Write async getAllBooks() method that returns this.prisma.book.findMany().

4

Export the service class

Make sure the BooksService class is exported using export class BooksService so it can be used in other parts of the NestJS app.

NestJS

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

const prisma = new PrismaClient();

// Ensure BooksService is exported
# Your code here

Hint

Use export class BooksService at the start of the class definition.

Practice

1. What is the main purpose of Prisma Client in a NestJS application?

easy

A. To interact with the database using simple JavaScript calls

B. To handle HTTP requests and routing

C. To manage application state in the frontend

D. To style components with CSS

Solution

1. Step 1: Understand Prisma Client's role

   Prisma Client is a tool that helps you talk to your database easily using JavaScript.

2. Step 2: Compare with other options

   Handling HTTP requests and routing, managing frontend state, and styling components relate to other parts of an app, not database interaction.

3. Final Answer:

   To interact with the database using simple JavaScript calls -> Option A

4. Quick Check:

   Prisma Client = database interaction [OK]

Hint: Prisma Client is for database queries, not UI or routing [OK]

Common Mistakes:

• Confusing Prisma Client with HTTP routing
• Thinking Prisma Client manages frontend state
• Assuming Prisma Client styles components

2. Which of the following is the correct way to import and instantiate Prisma Client in a NestJS service?

easy

A. import { PrismaClient } from '@prisma/client'; const prisma = new PrismaClient();

B. const prisma = require('prisma-client');

C. import Prisma from 'prisma'; const prisma = Prisma();

D. import { Prisma } from '@nestjs/prisma'; const prisma = new Prisma();

Solution

1. Step 1: Check the official import syntax

   The correct import is from '@prisma/client' and creating a new PrismaClient instance.

2. Step 2: Identify incorrect options

   Using require('prisma-client'), importing from 'prisma', or using '@nestjs/prisma' with incorrect instantiation do not match Prisma Client usage.

3. Final Answer:

   import { PrismaClient } from '@prisma/client'; const prisma = new PrismaClient(); -> Option A

4. Quick Check:

   Correct import and instantiation = import { PrismaClient } from '@prisma/client'; const prisma = new PrismaClient(); [OK]

Hint: Always import PrismaClient from '@prisma/client' and instantiate with new [OK]

Common Mistakes:

• Using require instead of import
• Wrong package names like 'prisma-client'
• Confusing NestJS modules with Prisma Client

3. Given this Prisma Client query in a NestJS service:

const user = await prisma.user.findUnique({ where: { id: 5 } });
console.log(user);

What will be logged if a user with id 5 exists in the database?

medium

A. An array of all users in the database

B. A syntax error

C. null

D. An object containing the user's data with id 5

Solution

1. Step 1: Understand findUnique behavior

   findUnique returns a single record matching the condition or null if none found.

2. Step 2: Given user with id 5 exists

   The query returns the user object with id 5, so console.log prints that object.

3. Final Answer:

   An object containing the user's data with id 5 -> Option D

4. Quick Check:

   findUnique with existing id = user object [OK]

Hint: findUnique returns one object or null, not array [OK]

Common Mistakes:

• Expecting an array instead of an object
• Assuming null even if user exists
• Thinking it causes syntax error

4. Identify the error in this NestJS Prisma Client usage:

import { PrismaClient } from '@prisma/client';
const prisma = new PrismaClient();

async function getUsers() {
  const users = prisma.user.findMany();
  return users;
}

medium

A. Function getUsers should not be async

B. Missing await before prisma.user.findMany()

C. findMany() does not exist on prisma.user

D. PrismaClient should not be instantiated directly

Solution

1. Step 1: Check async function usage

   prisma.user.findMany() returns a Promise, so it must be awaited inside async functions.

2. Step 2: Identify missing await

   The code misses 'await' before the call, so it returns a Promise instead of resolved data.

3. Final Answer:

   Missing await before prisma.user.findMany() -> Option B

4. Quick Check:

   Async DB calls need await [OK]

Hint: Await all Prisma async calls inside async functions [OK]

Common Mistakes:

• Forgetting await on async Prisma calls
• Thinking PrismaClient can't be instantiated
• Assuming findMany() is invalid

5. In a NestJS app, you want to ensure Prisma Client connects once on app start and disconnects on shutdown. Which approach is best?

hard

A. Call prisma.$connect() before every query and prisma.$disconnect() after every query

B. Create a new PrismaClient instance inside every controller method

C. Create PrismaClient instance in a service, call prisma.$connect() in onModuleInit(), and prisma.$disconnect() in onModuleDestroy()

D. Use PrismaClient without calling connect or disconnect methods

Solution

1. Step 1: Understand PrismaClient lifecycle

   PrismaClient should connect once when app starts and disconnect on shutdown to manage resources efficiently.

2. Step 2: Evaluate options

   Creating a single PrismaClient instance in a service and using $connect() in onModuleInit() and $disconnect() in onModuleDestroy() leverages NestJS lifecycle hooks properly. Connecting/disconnecting per query, creating new instances per method, or skipping explicit management leads to overhead or resource leaks.

3. Final Answer:

   Create PrismaClient instance in a service, call prisma.$connect() in onModuleInit(), and prisma.$disconnect() in onModuleDestroy() -> Option C

4. Quick Check:

   Use lifecycle hooks for Prisma connection [OK]

Hint: Connect once on start, disconnect on shutdown using lifecycle hooks [OK]

Common Mistakes:

• Creating PrismaClient multiple times
• Connecting/disconnecting on every query
• Ignoring connect/disconnect lifecycle