Server component database queries in NextJS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the database client in a Next.js server component.

NextJS

import [1] from '@/lib/prisma';

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

Aprisma

BReact

CuseState

Dfetch

Attempts:

3 left

💡 Hint

Common Mistakes

Importing React or hooks like useState which are for client components.

Trying to import 'fetch' as the database client.

You import the Prisma client instance named 'prisma' to query the database in server components.

2fill in blank

medium

Complete the code to fetch all users from the database inside a server component.

NextJS

const users = await prisma.user.[1]();

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

Acreate

BfindMany

CfindUnique

Ddelete

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'findUnique' which only fetches one record.

Using 'create' or 'delete' which modify data instead of fetching.

The 'findMany' method fetches all records from the 'user' table.

3fill in blank

hard

Fix the error in the server component query to fetch a user by ID.

NextJS

const user = await prisma.user.findUnique({ where: { id: [1] } });

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

Auser.id

Bid

Cparams.id

DuserId

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the string 'id' instead of the variable holding the ID.

Using 'user.id' which is undefined in this context.

You must pass the actual ID value, often from 'params.id' in Next.js server components.

4fill in blank

hard

Fill both blanks to create a server component that fetches posts and returns a list.

NextJS

export default async function Posts() {
  const posts = await prisma.post.[1]();
  return (
    <ul>
      {posts.map(post => <li key={post.[2]>{post.title}</li>)}
    </ul>
  );
}

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

AfindMany

Bid

Ctitle

Dcreate

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'create' instead of 'findMany' to fetch posts.

Using 'title' as the key which may not be unique.

Use 'findMany' to get all posts and 'id' as the unique key for list items.

5fill in blank

hard

Fill all three blanks to filter users older than 18 and map their names.

NextJS

const adults = await prisma.user.findMany({ where: { age: { [1]: [2] } } });
const names = adults.map(user => user.[3]);

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

Agt

B18

Cname

Dlt

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'lt' (less than) instead of 'gt'.

Mapping a property other than 'name'.

Use 'gt' (greater than) with 18 to filter adults, then map their 'name' property.

Practice

1. What is the main advantage of using server components in Next.js for database queries?

easy

A. They fetch data securely on the server without exposing credentials to the client.

B. They allow direct database access from the browser.

C. They require no async/await syntax for queries.

D. They automatically cache data on the client side.

Solution

1. Step 1: Understand server components role

   Server components run on the server, so they can safely access databases without exposing secrets to the client.

2. Step 2: Compare options

   Only They fetch data securely on the server without exposing credentials to the client. correctly states the security advantage. Options A, C, and D are incorrect because database access is not done in the browser, async/await is needed, and caching is not automatic on client side.

3. Final Answer:

   They fetch data securely on the server without exposing credentials to the client. -> Option A

4. Quick Check:

   Server components = secure server data fetching [OK]

Hint: Server components run on server, so data stays secure there [OK]

Common Mistakes:

• Thinking database queries run in the browser
• Ignoring async/await for fetching data
• Assuming client-side caching is automatic

2. Which of the following is the correct way to fetch data from a database inside a Next.js server component?

easy

A. const data = await db.query('SELECT * FROM users')

B. const data = fetch('api/data')

C. const data = db.query('SELECT * FROM users')

D. const data = useEffect(() => db.query('SELECT * FROM users'), [])

Solution

1. Step 1: Identify async database query syntax

   Database queries inside server components must use async/await to wait for the query result.

2. Step 2: Evaluate options

   const data = await db.query('SELECT * FROM users') uses await correctly. const data = fetch('api/data') uses fetch which is client-side. const data = db.query('SELECT * FROM users') misses await, so it returns a promise. const data = useEffect(() => db.query('SELECT * FROM users'), []) uses useEffect, which is a client hook and invalid in server components.

3. Final Answer:

   const data = await db.query('SELECT * FROM users') -> Option A

4. Quick Check:

   Async query = await db.query(...) [OK]

Hint: Use await with db queries inside async server components [OK]

Common Mistakes:

• Omitting await causing unresolved promises
• Using client hooks like useEffect in server components
• Using fetch instead of direct DB queries

3. Given this Next.js server component code, what will be rendered if the database returns [{ id: 1, name: 'Alice' }, { id: 2, name: 'Bob' }]?

export default async function Users() {
  const users = await db.query('SELECT id, name FROM users');
  return (
    <ul>
      {users.map(user => <li key={user.id}>{user.name}</li>)}
    </ul>
  );
}

medium

A. 12

B. AliceBob

C. Error: users.map is not a function

D. {user.name}{user.name}

Solution

1. Step 1: Understand data and rendering

   The database returns an array of user objects with id and name. The component maps over users and renders each name inside <li>.

2. Step 2: Check output correctness

   • Alice
   • Bob
   correctly shows the list with names Alice and Bob.
   • 1
   • 2
   shows ids instead of names. Error: users.map is not a function would happen if users was not an array.
   • {user.name}
   • {user.name}
   shows JSX code as text, which is incorrect.

3. Final Answer:

   <ul><li>Alice</li><li>Bob</li></ul> -> Option B

4. Quick Check:

   Mapping array to list items = names shown [OK]

Hint: Map array to JSX list to render names correctly [OK]

Common Mistakes:

• Rendering ids instead of names
• Forgetting to use key prop in list items
• Trying to render raw objects instead of properties

4. Identify the error in this Next.js server component fetching data from a database:

export default function Products() {
  const products = await db.query('SELECT * FROM products');
  return (
    <div>{products.length} products found</div>
  );
}

medium

A. products.length is invalid for query result

B. Cannot use await inside server components

C. Missing async keyword on the component function

D. db.query should be inside useEffect hook

Solution

1. Step 1: Check async usage in server component

   Await can only be used inside async functions. The component lacks the async keyword.

2. Step 2: Validate other options

   Cannot use await inside server components is wrong because await is allowed in server components if async is used. db.query should be inside useEffect hook is wrong because useEffect is client-only. products.length is invalid for query result is wrong because products is expected to be an array with length.

3. Final Answer:

   Missing async keyword on the component function -> Option C

4. Quick Check:

   Await requires async function [OK]

Hint: Add async before function to use await inside [OK]

Common Mistakes:

• Forgetting async keyword on server component
• Using client hooks like useEffect in server components
• Assuming query result is not an array

5. You want to fetch user data and their posts in a Next.js server component. Which approach correctly fetches both from the database before rendering?

export default async function UserPosts() {
  const user = await db.query('SELECT * FROM users WHERE id = 1');
  const posts = await db.query('SELECT * FROM posts WHERE userId = 1');
  return (
    <section>
      <h1>{user.name}</h1>
      <ul>
        {posts.map(post => <li key={post.id}>{post.title}</li>)}
      </ul>
    </section>
  );
}

What is the best way to optimize these queries?

hard

A. Fetch posts on the client side using useEffect

B. Run the second query inside the map function for posts

C. Combine both queries into one SQL join query

D. Run both queries in parallel using Promise.all before rendering

Solution

1. Step 1: Understand query optimization

   Running queries sequentially waits for the first before starting the second, slowing response.

2. Step 2: Evaluate options for optimization

   Run both queries in parallel using Promise.all before rendering runs both queries in parallel with Promise.all, improving speed. Run the second query inside the map function for posts runs queries inside map, causing many queries (bad). Fetch posts on the client side using useEffect moves fetching to client, losing server benefits. Combine both queries into one SQL join query is possible but may complicate data handling.

3. Final Answer:

   Run both queries in parallel using Promise.all before rendering -> Option D

4. Quick Check:

   Parallel queries = faster data fetching [OK]

Hint: Use Promise.all to fetch multiple queries simultaneously [OK]

Common Mistakes:

• Running queries one after another sequentially
• Fetching data inside loops causing many queries
• Moving server data fetching to client side unnecessarily