# ConflictException

**Kind:** Class

**Source:** [`packages/common/exceptions/conflict.exception.ts`](https://github.com/nestjs/nest/blob/master/packages/common/exceptions/conflict.exception.ts#L11)

**Part of:** [Common](subsystem-packages-common)

Defines an HTTP exception for *Conflict* type errors.

`ConflictException` represents an HTTP 409 Conflict error. Use it when a request cannot be completed because it conflicts with the current state of a resource, such as attempting to create a record that already exists.

**Extends:** `HttpException`

## Diagram

```mermaid
graph LR
  A[Application logic] -->|Detects conflicting state| B[ConflictException]
  B --> C[HTTP exception handler]
  C -->|HTTP 409 Conflict response| D[Client]
```

## Usage

```ts
import { ConflictException } from '@nestjs/common';

async function createUser(email: string) {
  const existingUser = await usersRepository.findByEmail(email);

  if (existingUser) {
    throw new ConflictException(
      `A user with email "${email}" already exists.`,
    );
  }

  return usersRepository.create({ email });
}
```

## AI Coding Instructions

- Throw `ConflictException` only for resource-state conflicts, such as duplicate unique fields or incompatible concurrent updates.
- Prefer a clear, client-safe error message that explains which conflict occurred without exposing sensitive data.
- Do not use this exception for validation failures; use a bad-request or validation-specific exception instead.
- Let the framework’s global exception handling convert the exception into the standard HTTP 409 response.