[Fixed] Error: No response is returned from route handler in next.js

Quick Fix: Utilize Promises to assure completion of database query before sending a response, handling errors gracefully.

The Problem:

An error occurs when attempting to fetch data from a MySQL database using API routes in Next.js. Upon calling the API route, the error message "Error: No response is returned from route handler" is displayed. The provided code snippet handles the GET request, queries the database, and intends to return a JSON response with the results or an error message. However, the error message suggests that the route handler is not properly sending a response back to the client.

The Solutions:

Solution 1: Using Promises

The issue with the original code is that it is using db.query in an asynchronous manner, and the response is being returned before the query is complete. To fix this, we can use Promises to wait for the query to finish before returning the response. Here’s the modified code:

<!– begin snippet: js hide: false console: true babel: false –>

<!– language: lang-js –>

export function GET(request){
  try {
    const results = await new Promise((resolve, reject) =&gt; {
      db.query(&#39;SELECT * FROM department&#39;, (error, results, fields) =&gt; {
        if (error) {
          reject(error);
        } else {
          resolve(results);
        }
      });
    });

    return NextResponse.json({ data: results }, { status: 201 });
  } catch (error) {
    return NextResponse.json({ error: error}, { status: 500 });
  }
}

<!– end snippet –>

We wrap the db.query call within a try-catch block to handle any errors that may occur during the query execution.
Inside the try block, we create a new Promise and pass it a resolve and reject function.
We then call the db.query function and pass the resolve and reject functions as callbacks.
When the query is complete, we either call resolve to resolve the Promise with the query results or reject to reject the Promise with the error.
We use the await keyword to wait for the Promise to resolve before returning the response. If the Promise is rejected, we catch the error and return an error response.

By using Promises, we ensure that the response is only returned once the query is complete, preventing the "No response is returned from route handler" error.

Q&A

Why does the error "No response is returned from route handler" occur in this next.js code that fetches data from a MySQL database?

—

The error is because the route handler returns a response before the asynchronous db.query is complete.

How to fix the error "No response is returned from route handler" in this next.js code?

—

Use promises to make the db.query function synchronous, ensuring that the data is fetched before returning a response.

Video Explanation:

The following video, titled "Full Stack Authentication with Next-Auth and Next.js 13: All You ...", provides additional insights and in-depth exploration related to the topics discussed in this post.