使用 mysql 和 node.js 的自定义前缀

Question

var prefix = `SELECT S_PREFIX FROM ServerConfigs WHERE S_ID = ${message.guild.id}`; connection.query(prefix, function (err, result, fields) { if (err) return console.log(err); let res = JSON.parse(JSON.stringify(result[0].S_PREFIX)); const serverPREFIX = res;

It works but sometimes it writes me an error to console. The error looks like this: TypeError: Cannot read property 'S_PREFIX' of undefined

Could anybody help me please? Just started learning MYSQL.

Answer 1

result[0] is undefined , which means that your SQL query returned no results, meaning that there were no rows with the S_ID being message.guild.id . Just check that the result array is not empty.

var prefix = `SELECT S_PREFIX FROM ServerConfigs WHERE S_ID = ${message.guild.id}`;
connection.query(prefix, function (err, result, fields) {
  if (err) return console.log(err);
  if (result.length < 1) {
    console.log(`No results for S_ID = ${message.guild.id}`)
    return;
  }
  let res = JSON.parse(JSON.stringify(result[0].S_PREFIX));
  const serverPREFIX = res;