Why Prisma offers type-safe database access in NestJS - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import PrismaClient correctly in a NestJS service.

NestJS

import { [1] } from '@prisma/client';

Drag options to blanks, or click blank then click option'

AClient

BDatabaseClient

CPrismaService

DPrismaClient

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong class name that does not exist in '@prisma/client'.

Confusing PrismaClient with service classes.

PrismaClient is the main class provided by Prisma to interact with the database in a type-safe way.

2fill in blank

medium

Complete the code to create a new PrismaClient instance in the service constructor.

NestJS

constructor() {
  this.prisma = new [1]();
}

Drag options to blanks, or click blank then click option'

AClient

BDatabaseClient

CPrismaClient

DPrismaService

Attempts:

3 left

💡 Hint

Common Mistakes

Using a class name that is not imported or does not exist.

Forgetting to instantiate the client with 'new'.

Creating a new instance of PrismaClient allows the service to access the database with type safety.

3fill in blank

hard

Fix the error in the method to fetch all users using Prisma's type-safe API.

NestJS

async getAllUsers() {
  return await this.prisma.user.[1]();
}

Drag options to blanks, or click blank then click option'

AfindAll

BfindMany

CgetAll

DfetchAll

Attempts:

3 left

💡 Hint

Common Mistakes

Using non-existent Prisma methods like 'findAll' or 'getAll'.

Confusing Prisma methods with other ORM methods.

The correct Prisma method to fetch multiple records is findMany(), which returns a typed array of users.

4fill in blank

hard

Fill both blanks to define a type-safe method that finds a user by ID.

NestJS

async getUserById(id: number) {
  return await this.prisma.user.[1]({ where: { id: [2] } });
}

Drag options to blanks, or click blank then click option'

AfindUnique

BfindMany

Cid

DuserId

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'findMany' when only one record is expected.

Using a wrong field name in the where clause.

findUnique is used to find a single record by a unique field like id, ensuring type safety.

5fill in blank

hard

Fill all three blanks to create a type-safe method that updates a user's email by ID.

NestJS

async updateUserEmail(id: number, email: string) {
  return await this.prisma.user.[1]({
    where: { id: [2] },
    data: { email: [3] }
  });
}

Drag options to blanks, or click blank then click option'

Aupdate

Bid

Cemail

DfindUnique

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'findUnique' instead of 'update' for updating data.

Mixing up field names in the where or data objects.

The update method updates a record. The where clause uses the id field, and the data object sets the new email. This ensures type-safe updates.

Practice

1. Why does Prisma provide type-safe database access in NestJS applications?

easy

A. To replace the need for SQL queries entirely

B. To make the database run faster

C. To automatically create database backups

D. To catch errors early by matching queries to the database schema

Solution

1. Step 1: Understand Prisma's purpose

   Prisma checks that your code queries match the database structure to avoid mistakes.

2. Step 2: Identify the benefit of type safety

   This early error detection helps developers write safer and more reliable code.

3. Final Answer:

   To catch errors early by matching queries to the database schema -> Option D

4. Quick Check:

   Type safety = early error detection [OK]

Hint: Type safety means catching mistakes before running code [OK]

Common Mistakes:

• Thinking Prisma speeds up the database itself
• Confusing type safety with backups
• Believing Prisma removes all SQL usage

2. Which of the following is the correct way to import Prisma Client in a NestJS service for type-safe access?

easy

A. const { Prisma } = require('@prisma/client');

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

C. import Prisma from 'prisma';

D. const PrismaClient = require('prisma-client');

Solution

1. Step 1: Check official Prisma import syntax

   Prisma Client is imported using ES module syntax: import { PrismaClient } from '@prisma/client';

2. Step 2: Identify incorrect options

   Options A, B, and C use wrong module names or CommonJS require syntax not recommended in NestJS with ES modules.

3. Final Answer:

   import { PrismaClient } from '@prisma/client'; -> Option B

4. Quick Check:

   Correct import syntax = import { PrismaClient } from '@prisma/client'; [OK]

Hint: Use ES module import syntax for Prisma Client [OK]

Common Mistakes:

• Using require() instead of import
• Wrong package names like 'prisma-client'
• Destructuring Prisma instead of PrismaClient

3. Given this Prisma query in a NestJS service:

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

What will happen if the id field does not exist in the database schema?

medium

A. The query will run but return null

B. The database will ignore the id filter

C. TypeScript will show a compile-time error

D. The application will crash at runtime

Solution

1. Step 1: Understand Prisma's type safety

   Prisma generates types from the database schema, so invalid fields cause TypeScript errors before running.

2. Step 2: Identify error timing

   Since id is missing, TypeScript will catch this mismatch during compilation, preventing runtime errors.

3. Final Answer:

   TypeScript will show a compile-time error -> Option C

4. Quick Check:

   Invalid field = compile-time error [OK]

Hint: Prisma type safety catches wrong fields before running code [OK]

Common Mistakes:

• Assuming runtime crash instead of compile error
• Thinking database ignores unknown fields silently
• Believing query returns null without error

4. You wrote this Prisma query in NestJS:

const posts = await prisma.post.findMany({ where: { title: 'Hello' } });

But you get a TypeScript error: Property 'title' does not exist on type 'PostWhereInput'.
What is the most likely cause?

medium

A. The title field is missing in the Prisma schema for Post

B. You forgot to import PrismaClient

C. The database connection is not established

D. You used findMany instead of findUnique

Solution

1. Step 1: Analyze the TypeScript error

   The error says title is not a valid filter field, meaning it is not defined in the Prisma schema for Post.

2. Step 2: Rule out other options

   Missing import or connection issues cause different errors; findMany is valid here.

3. Final Answer:

   The title field is missing in the Prisma schema for Post -> Option A

4. Quick Check:

   Missing schema field = TypeScript error [OK]

Hint: Check Prisma schema fields if TypeScript errors on filters [OK]

Common Mistakes:

• Blaming database connection for type errors
• Confusing method names causing this error
• Ignoring schema updates after changes

5. In a NestJS app using Prisma, you want to ensure your database queries are type-safe and reflect the latest schema changes. Which approach best achieves this?

hard

A. Run prisma generate after updating the Prisma schema file

B. Manually write TypeScript types for your database models

C. Use raw SQL queries inside Prisma without type checks

D. Disable type checking in your IDE

Solution

1. Step 1: Understand Prisma's code generation

   Running prisma generate updates the generated client with types matching the current schema.

2. Step 2: Evaluate other options

   Manual types risk errors; raw SQL skips type safety; disabling checks removes benefits.

3. Final Answer:

   Run prisma generate after updating the Prisma schema file -> Option A

4. Quick Check:

   Generate client = updated type safety [OK]

Hint: Always run prisma generate after schema changes [OK]

Common Mistakes:

• Writing manual types instead of generating
• Ignoring schema updates in code
• Disabling helpful type checks