Prisma Client usage in NestJS

Introduction

Prisma Client helps you talk to your database easily. It lets you get, add, change, or delete data without writing complex SQL.

When you want to read data from your database in a NestJS app.

When you need to add new records to your database safely.

When you want to update or delete data based on user actions.

When you want to avoid writing raw SQL queries and use simple JavaScript instead.

Syntax

NestJS

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

const prisma = new PrismaClient();

// Example: Get all users
async function main() {
  const users = await prisma.user.findMany();
  console.log(users);
}

main();

PrismaClient is imported from '@prisma/client' and instantiated once.

Use async/await to handle database calls because they return promises.

Examples

Fetches all users from the 'user' table.

NestJS

const allUsers = await prisma.user.findMany();

Adds a new user with name and email.

NestJS

const newUser = await prisma.user.create({ data: { name: 'Anna', email: '[e-mail]' } });

Changes the name of the user with id 1.

NestJS

const updatedUser = await prisma.user.update({ where: { id: 1 }, data: { name: 'Anna Smith' } });

Removes the user with id 1 from the database.

NestJS

const deletedUser = await prisma.user.delete({ where: { id: 1 } });

Sample Program

This NestJS service uses Prisma Client to connect to the database, add a user, and fetch all users. It connects when the module starts and disconnects when it stops.

NestJS

import { Injectable, OnModuleInit, OnModuleDestroy } from '@nestjs/common';
import { PrismaClient } from '@prisma/client';

@Injectable()
export class UserService implements OnModuleInit, OnModuleDestroy {
  private prisma = new PrismaClient();

  async onModuleInit() {
    await this.prisma.$connect();
  }

  async onModuleDestroy() {
    await this.prisma.$disconnect();
  }

  async getAllUsers() {
    return await this.prisma.user.findMany();
  }

  async createUser(name: string, email: string) {
    return await this.prisma.user.create({
      data: { name, email },
    });
  }
}

// Example usage (in some controller or main file):
async function main() {
  const userService = new UserService();
  await userService.onModuleInit();

  const newUser = await userService.createUser('John Doe', '[e-mail]');
  console.log('Created user:', newUser);

  const users = await userService.getAllUsers();
  console.log('All users:', users);

  await userService.onModuleDestroy();
}

main();

Important Notes

Always connect to the database before queries and disconnect after to avoid resource leaks.

Prisma Client methods return promises, so use async/await or .then() to handle results.

Use the Prisma schema file to define your database models before generating Prisma Client.

Summary

Prisma Client lets you work with your database using simple JavaScript calls.

Use it in NestJS by importing and creating a PrismaClient instance.

Remember to connect and disconnect Prisma Client properly in your app lifecycle.

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