Server action database mutations in NextJS

Introduction

Server action database mutations let you change data on the server safely and easily. They help keep your app data updated without extra setup.

When you want to add new data to your database from a form.

When you need to update existing data after user input.

When you want to delete data securely from the server.

When you want to keep your UI and database in sync automatically.

When you want to avoid writing separate API routes for simple data changes.

Syntax

NextJS

'use server'

export async function actionName(formData: FormData) {
  // perform database mutation here
  await db.model.create({ data: { /* your data here */ } })
  // optionally return data or redirect
}

Use the 'use server' directive at the top of the function to mark it as a server action.

The function receives form data or parameters and performs database changes directly.

Examples

This server action adds a new user with the name from a form.

NextJS

'use server'

export async function addUser(formData: FormData) {
  const name = formData.get('name')?.toString() || ''
  await db.user.create({ data: { name } })
}

This server action deletes a post by its ID.

NextJS

'use server'

export async function deletePost(postId: string) {
  await db.post.delete({ where: { id: postId } })
}

Sample Program

This example shows a simple todo form. When submitted, it calls the addTodo server action to add a new todo item to the database. The form uses semantic HTML and accessibility labels.

NextJS

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

'use server'

export async function addTodo(formData: FormData) {
  const title = formData.get('title')?.toString() || ''
  if (title.trim() === '') return
  await db.todo.create({ data: { title } })
}

export default function TodoForm() {
  return (
    <form action={addTodo}>
      <label htmlFor="title">New Todo:</label>
      <input id="title" name="title" type="text" required aria-label="Todo title" />
      <button type="submit">Add</button>
    </form>
  )
}

Important Notes

Server actions run only on the server, so they keep your database credentials safe.

Use FormData to get form inputs easily inside the action.

Server actions simplify data mutations without needing separate API routes.

Summary

Server action database mutations let you change data on the server directly.

They use the 'use server' directive and receive form data or parameters.

This approach keeps your app secure and your code simple.

Practice

1. What is the main purpose of using server actions for database mutations in Next.js?

easy

A. To run client-side animations after data changes

B. To securely update data on the server without exposing logic to the client

C. To fetch data from an external API on the client

D. To style components dynamically based on user input

Solution

1. Step 1: Understand server actions role

   Server actions run on the server and handle data changes securely.

2. Step 2: Identify the security benefit

   They keep mutation logic hidden from the client, preventing misuse.

3. Final Answer:

   To securely update data on the server without exposing logic to the client -> Option B

4. Quick Check:

   Server actions = secure server-side mutations [OK]

Hint: Server actions run on server to keep data safe [OK]

Common Mistakes:

• Thinking server actions run on the client
• Confusing server actions with client-side fetching
• Believing server actions handle UI styling

2. Which of the following is the correct way to declare a server action function in Next.js?

easy

A. export async function addUser() { 'use server'; /* mutation code */ }

B. export async function addUser() { useServer(); /* mutation code */ }

C. export async function addUser() { /* mutation code */ } 'use server';

D. 'use server'; export async function addUser() { /* mutation code */ }

Solution

1. Step 1: Identify correct 'use server' placement

   The 'use server' directive must be the first statement inside the function file or function scope.

2. Step 2: Check syntax correctness

   'use server'; export async function addUser() { /* mutation code */ } places 'use server' at the top before the function, which is correct syntax.

3. Final Answer:

   'use server'; export async function addUser() { /* mutation code */ } -> Option D

4. Quick Check:

   'use server' directive must be at top [OK]

Hint: Put 'use server' at the top before function export [OK]

Common Mistakes:

• Placing 'use server' inside function body after code
• Using a function call like useServer() instead of directive
• Putting 'use server' after function declaration

3. Given this server action code, what will be the result after calling await addUser({ name: 'Alice' }) if the database is empty?

 'use server';
 async function addUser(user) {
   await db.users.create({ data: user });
   return await db.users.count();
 }

medium

A. Returns 1 because one user is added

B. Returns undefined because no return statement

C. Throws an error because 'use server' is misplaced

D. Returns 0 because count is called before creation

Solution

1. Step 1: Analyze database mutation

   The function creates a user in the database with given data.

2. Step 2: Check return value

   After creation, it returns the count of users, which should be 1.

3. Final Answer:

   Returns 1 because one user is added -> Option A

4. Quick Check:

   Created one user, count = 1 [OK]

Hint: Create then count means count reflects new data [OK]

Common Mistakes:

• Assuming count runs before creation completes
• Confusing 'use server' placement causing error
• Missing return statement in function

4. Identify the error in this server action code snippet:

'use server';
export async function updateUser(id, data) {
  await db.users.update({ where: { id }, data });
}

medium

A. Missing semicolon after 'use server' directive

B. Missing export keyword

C. Incorrect object structure in update call

D. No error, code is correct

Solution

1. Step 1: Check 'use server' directive syntax

   The 'use server'; directive is correctly placed at the top of the module.

2. Step 2: Analyze update method parameters

   The update method expects an object with 'where' and 'data' keys, but here 'data' is outside the object, causing syntax error.

3. Final Answer:

   Incorrect object structure in update call -> Option C

4. Quick Check:

   update expects { where: ..., data: ... } object [OK]

Hint: Check object keys carefully in db update calls [OK]

Common Mistakes:

• Assuming missing semicolon causes error
• Forgetting to wrap data inside update object
• Missing export keyword (actually present)

5. You want to create a server action that deletes a user only if they have no active orders. Which approach correctly combines server action and database mutation logic?

 'use server';
 async function deleteUserIfNoOrders(userId) {
   const orders = await db.orders.findMany({ where: { userId, status: 'active' } });
   if (orders.length === 0) {
     await db.users.delete({ where: { id: userId } });
     return 'Deleted';
   }
   return 'Has active orders';
 }

hard

A. This code correctly checks orders before deleting user

B. This code deletes user without checking orders

C. This code will throw error because 'use server' is misplaced

D. This code returns 'Deleted' even if user has active orders

Solution

1. Step 1: Verify order check logic

   The function queries active orders for the user and checks if none exist.

2. Step 2: Confirm conditional deletion

   If no active orders, it deletes the user and returns 'Deleted'; otherwise returns 'Has active orders'.

3. Final Answer:

   This code correctly checks orders before deleting user -> Option A

4. Quick Check:

   Conditional delete based on orders = correct [OK]

Hint: Check conditions before mutation to avoid unwanted deletes [OK]

Common Mistakes:

• Deleting user without checking orders first
• Misplacing 'use server' directive
• Returning wrong message ignoring condition