Why database access matters in NextJS - See It in Action

Why database access matters

📖 Scenario: You are building a simple Next.js app that shows a list of books from a database. This app helps users see available books easily.

🎯 Goal: Build a Next.js component that fetches book data from a database and displays it on the page.

📋 What You'll Learn

Create a mock database array of book objects

Add a configuration variable for minimum rating filter

Use a function to filter books by rating

Render the filtered books in a Next.js component

💡 Why This Matters

🌍 Real World

Many web apps need to get data from databases and show only relevant information to users, like filtering products or articles.

💼 Career

Understanding how to access and filter database data in Next.js is essential for building dynamic, user-friendly web applications.

1

DATA SETUP: Create a mock database array

Create a constant array called books with these exact objects: { id: 1, title: 'The Great Gatsby', rating: 4.3 }, { id: 2, title: '1984', rating: 4.7 }, and { id: 3, title: 'Moby Dick', rating: 3.9 }.

NextJS

// Create the books array with the given objects
// Your code here

Hint

Use const books = [ ... ] with the exact objects inside.

2

CONFIGURATION: Add a minimum rating filter

Create a constant called minRating and set it to 4.0 to filter books by rating.

NextJS

const books = [
  { id: 1, title: 'The Great Gatsby', rating: 4.3 },
  { id: 2, title: '1984', rating: 4.7 },
  { id: 3, title: 'Moby Dick', rating: 3.9 }
];

// Create minRating constant
// Your code here

Hint

Use const minRating = 4.0; exactly.

3

CORE LOGIC: Filter books by minimum rating

Create a constant called filteredBooks that filters books to include only those with rating greater than or equal to minRating using books.filter().

NextJS

const books = [
  { id: 1, title: 'The Great Gatsby', rating: 4.3 },
  { id: 2, title: '1984', rating: 4.7 },
  { id: 3, title: 'Moby Dick', rating: 3.9 }
];

const minRating = 4.0;

// Filter books by minRating
// Your code here

Hint

Use books.filter(book => book.rating >= minRating) to create filteredBooks.

4

COMPLETION: Render filtered books in a Next.js component

Create a default exported React functional component called BooksList that returns a <ul> with each filteredBooks item rendered as a <li> showing the book title and rating. Use book.id as the key.

NextJS

const books = [
  { id: 1, title: 'The Great Gatsby', rating: 4.3 },
  { id: 2, title: '1984', rating: 4.7 },
  { id: 3, title: 'Moby Dick', rating: 3.9 }
];

const minRating = 4.0;

const filteredBooks = books.filter(book => book.rating >= minRating);

// Create BooksList component
// Your code here

Hint

Use export default function BooksList() and return a <ul> with filteredBooks.map() rendering <li key={book.id}> showing title and rating.

Practice

1. Why is database access important in a Next.js application?

easy

A. It allows the app to save and retrieve changing data securely.

B. It makes the app load faster by skipping data storage.

C. It replaces the need for any server-side code.

D. It only helps with styling the user interface.

Solution

1. Step 1: Understand the role of database access

   Database access lets the app save and get data that changes over time, like user info or posts.

2. Step 2: Connect to Next.js usage

   Next.js uses server-side code to safely handle database calls, ensuring data is secure and fast to access.

3. Final Answer:

   It allows the app to save and retrieve changing data securely. -> Option A

4. Quick Check:

   Database access = save and retrieve data [OK]

Hint: Database access means saving and getting data safely [OK]

Common Mistakes:

• Thinking database access is only for styling
• Believing it replaces server-side code
• Assuming it makes the app load without data

2. Which Next.js file is the best place to put database access code?

easy

A. Inside a React client component's event handler

B. Directly inside the CSS files

C. In a server component or API route

D. In the public folder for static assets

Solution

1. Step 1: Identify where database calls should run

   Database access should happen on the server side to keep data safe and avoid exposing secrets.

2. Step 2: Match with Next.js structure

   Server components and API routes run on the server, so they are the right place for database code.

3. Final Answer:

   In a server component or API route -> Option C

4. Quick Check:

   Server code = database access place [OK]

Hint: Put database code in server components or API routes [OK]

Common Mistakes:

• Putting database code in client components
• Trying to access database in CSS or public folder
• Exposing database secrets in client code

3. What will this Next.js server component do?

import { db } from '@/lib/db';

export default async function Page() {
  const users = await db.user.findMany();
  return (
    <ul>
      {users.map(user => <li key={user.id}>{user.name}</li>)}
    </ul>
  );
}

medium

A. Render a list of user names fetched from the database

B. Throw an error because db.user.findMany() is invalid

C. Render an empty list because users is undefined

D. Show a loading spinner indefinitely

Solution

1. Step 1: Understand the database call

   The code calls db.user.findMany() to get all users from the database asynchronously.

2. Step 2: Analyze the rendering

   The users array is mapped to list items showing each user's name inside an unordered list.

3. Final Answer:

   Render a list of user names fetched from the database -> Option A

4. Quick Check:

   db call + map users = list output [OK]

Hint: Async db calls return data to render lists [OK]

Common Mistakes:

• Assuming db.user.findMany() is invalid syntax
• Thinking users is undefined without await
• Expecting a loading spinner without client code

4. Identify the error in this Next.js API route accessing a database:

export default function handler(req, res) {
  const users = db.user.findMany();
  res.status(200).json(users);
}

medium

A. db.user.findMany() is not a valid method

B. Using res.status instead of res.send

C. API routes cannot return JSON

D. Missing async/await for the database call

Solution

1. Step 1: Check database call usage

   db.user.findMany() returns a promise, so it must be awaited or handled asynchronously.

2. Step 2: Fix the handler function

   The handler should be async and await the database call before sending the response.

3. Final Answer:

   Missing async/await for the database call -> Option D

4. Quick Check:

   Async db calls need await [OK]

Hint: Always await async database calls in API routes [OK]

Common Mistakes:

• Forgetting async keyword on handler
• Not awaiting the promise from db calls
• Confusing res.status with res.send usage

5. You want to show a list of posts with their authors' names in a Next.js server component. Which approach correctly handles database access to avoid slow page loads?

Option A:
const posts = await db.post.findMany({ include: { author: true } });
return posts.map(p => <div key={p.id}>{p.title} by {p.author.name}</div>);

Option B:
const posts = await db.post.findMany();
const authors = await db.user.findMany();
return posts.map(p => <div key={p.id}>{p.title} by {authors.find(a => a.id === p.authorId).name}</div>);

Option C:
Fetch posts on client side and authors on server side separately.

Option D:
Render posts without author names to speed up loading.

hard

A. Fetch posts and authors separately and match in code

B. Use a single query with include to fetch posts and authors together

C. Split fetching between client and server components

D. Skip author names to improve speed

Solution

1. Step 1: Analyze database query efficiency

   Use a single query with include to fetch posts and authors together, reducing database calls and speeding up loading.

2. Step 2: Compare other options

   Fetch posts and authors separately and match in code makes two queries, which is slower. Split fetching between client and server components causes complexity. Skip author names to improve speed loses important info.

3. Final Answer:

   Use a single query with include to fetch posts and authors together -> Option B

4. Quick Check:

   One query with include = faster load [OK]

Hint: Fetch related data in one query using include [OK]

Common Mistakes:

• Making multiple separate queries instead of one
• Fetching data on client causing slower loads
• Removing needed info to speed up page