NodeJS 在 MySQL 查询函数中返回“未定义”

Question

I have a function that queries SQL to get a string called Prefix.

function getPrefix(Guild) {
    let query = "SELECT Prefix FROM Guilds WHERE GuildId=?";
    Connection.query(query, [Guild.id], (err, result) => {
        if (err) throw err;
        return result[0].GuildPrefix;
    });
};

Whenever I print the Prefix out ( console.log(result[0].Prefix); ), it logs it fine - however, whenever I return it and then attempt to call the function, it always returns undefined.

I am using Node JS Version 10.15.1 & I am using MariaDB Version 10.1.37 on the Raspbian stretch of Debian. Please comment if I have left any other information out. Thanks.

Answer 1

In Nodejs the functions related to mysql are always asynchronous which means they will either not return anything or will retuen undefined.

So the solution is to use a callback function.
Eg.

function getPrefix(Guild, callback) {
    let query = "SELECT Prefix FROM Guilds WHERE GuildId=?";
    Connection.query(query, [Guild.id], (err, result) => {
        if (err){
         callback(JSON.stringify(err));
        };
        callback(JSON.stringify(result));
    });
};