Question 113266 in Mysql Question posted in
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Express and MySql

When I’m sending a POST request to MySql database, it adds the product but it shoots me with that error.

Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
at new NodeError (node:internal/errors:387:5)
at ServerResponse.setHeader (node:_http_outgoing:603:11)
at ServerResponse.header (C:UsersDELLDesktopSmall projectnode_modulesexpresslibresponse.js:794:10)
at ServerResponse.send (C:UsersDELLDesktopSmall projectnode_modulesexpresslibresponse.js:174:12)
at Query. (C:UsersDELLDesktopSmall projectserver.js:47:16)
at Query. (C:UsersDELLDesktopSmall projectnode_modulesmysqllibConnection.js:526:10)
at Query._callback (C:UsersDELLDesktopSmall projectnode_modulesmysqllibConnection.js:488:16)
at Query.Sequence.end (C:UsersDELLDesktopSmall projectnode_modulesmysqllibprotocolsequencesSequence.js:83:24)
at Query._handleFinalResultPacket (C:UsersDELLDesktopSmall projectnode_modulesmysqllibprotocolsequencesQuery.js:149:8)
at Query.OkPacket (C:UsersDELLDesktopSmall projectnode_modulesmysqllibprotocolsequencesQuery.js:74:10) {
code: ‘ERR_HTTP_HEADERS_SENT’

app.post("/product", (req, res, next) => {
  let product = {
    product_title: "lool",
    product_price: 4444.12,
    product_type: "sneakers",
    product_brand: "lol",
  };
  let sql = `INSERT INTO products SET ?`;

  db.query(sql, product, (err, result) => {
    if (err) {
      throw err;
    }
    console.log(result);
    return res.send("Completed");
  });

  res.send("Added");
});
Tags:

2

Answers


  1. 0

    You can only use res.send() once, when you use it a second time it throws this error. Just remove this res.send("Added").

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  2. 0

    If you’re writing asynchronous code, you must keep in mind the timing involved, and you must schedule your responses accordingly:

    app.post("/product", (req, res, next) => {
  // ...
  db.query(sql, product, (err, result) => {
    // ...

    // Runs at some point in the distant future in terms of compute time
    return res.send("Completed");
  });

  // Runs *immediately*
  res.send("Added");
});

    You cannot have that immediate res.send(), you must remove that. If you want to handle the error, that error handling happens inside the callback.1

    —

    1 This is why using async functions with await makes your code a lot easier to manage.

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