javascript - 错误 [ERR_HTTP_HEADERS_SENT] : Cannot set headers after they are sent to the client (multiple data entries)

Question

因此，我尝试插入然后更新数据，数据库已根据预期查询成功更新，并且能够接收对客户端的响应，但在服务器上收到上述错误，不知道如何调试它，我'我尝试查看之前的相关问题，但没有成功。

var urlencodedParser = bodyParser.urlencoded({ extended: false });
router.post('/createprovision', urlencodedParser,(req, res) => {
    let serials = [];
    for (let i = 0; i < req.body.length; i++){
        serials.push(req.body[i][1]);
    }  

    let sql = 'INSERT INTO provision (employee_id, serial_no, provision_date) VALUES ?';
    connection.query(sql, [req.body],(err, results) => {
        for(let i = 0; i < serials.length; i++){
            let sql2 = `UPDATE inventory SET ? WHERE serial_no = '${serials[i]}'`;
            connection.query(sql2, [{status: "assigned"}],(err, results) => {
                if (err) throw err;
                return res.send("provision success!");
            });
        }
    });
});

ERR_MSG:

Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client (multiple data entries)

Answer 1

您已将 return res.send("provision success!"); 放入 for 循环内，这意味着您在第一次迭代中向客户端发送响应，然后您尝试再次发送响应，但 header 已发送。将其放在函数末尾，仅在处理所有serials后发送响应。