prisma nextjs Type error: Type '(req: NextApiRequest, res: NextApiResponse) => Promise | undefined>' is not assignable to type 'NextApiHandler'.

Explanation of the Error

The error message you are encountering is related to a type mismatch in a Next.js application that uses Prisma. The error message specifically states that a certain type is not assignable to another type. Let's break down the error message to understand it better.

Understanding the Error Message

The error message states: "Type '(req: NextApiRequest, res: NextApiResponse) => Promise | undefined>' is not assignable to type 'NextApiHandler'."

  • The error is related to a type mismatch.
  • The type being assigned is a function with parameters (req: NextApiRequest, res: NextApiResponse) and a return type of Promise | undefined.
  • The type being assigned to is NextApiHandler.

Explanation of Types

To understand the error message, we need to understand the types involved:

  1. NextApiRequest: This is a type provided by Next.js and represents the incoming HTTP request.
  2. NextApiResponse: This is a type provided by Next.js and represents the outgoing HTTP response.
  3. NextApiHandler: This is a type provided by Next.js and represents the handler function for an API route. It is the type expected for the handler function in Next.js API routes.

Explanation of the Error

The error message is indicating that the function you are trying to assign to the handler of an API route does not match the expected type.

The expected type for the handler function in Next.js API routes is NextApiHandler. However, the function you are trying to assign has a different type: (req: NextApiRequest, res: NextApiResponse) => Promise | undefined.

The error message suggests that the function should be modified to match the expected type.

Solution

To resolve the error, you need to ensure that the function you are assigning to the API route handler has the correct type.

In this case, you need to modify the function signature to match the NextApiHandler type. The correct function signature should be:

import { NextApiHandler } from 'next';

const handler: NextApiHandler = async (req, res) => {
  // Your API route logic here
};

Make sure to import NextApiHandler from the next package and assign it to the handler function.

By using the correct type, the error should be resolved, and the function should be assignable to the NextApiHandler type.

Example

Here's an example of how the modified code should look:

import { NextApiHandler } from 'next';

const handler: NextApiHandler = async (req, res) => {
  // Your API route logic here
};

export default handler;

Ensure that you replace // Your API route logic here with your actual API route logic.

Conclusion

In summary, the error message you encountered is related to a type mismatch in a Next.js application that uses Prisma. The error message suggests that the function you are trying to assign to the API route handler does not match the expected type. To resolve the error, you need to modify the function signature to match the NextApiHandler type.