sqlite3 nodejs 从表中获取值 [英] sqlite3 nodejs get value from table

问题描述

我的 db.js 中有函数 getName

I've got the function getName in my db.js

function getName(uid){
    db.all("SELECT name FROM table WHERE uid = ? ",  function (err){
        if(err){
            console.log(err);
        }else{
            console.log(this);
        }
    });
}

我想获取名称并将其保存到另一个文件中的 var name.

and I want to get the name and save it to var name in another file.

var uid = req.session.user; 

var name = db.getName(uid);
      console.log(name);

db 函数 getname 有什么问题，为什么我没有定义?如果你能帮助我就太好了！

what is wrong about the db function getname why do I get undefined? Would be great if you could help me!

推荐答案

从异步函数返回数据可能会返回 undefined，因为在执行 return 语句时数据库请求可能尚未完成.

Returning data from an async function might return undefined as the database request might not have completed on execution of return statement.

function getName(uid, callback){
  var query = "SELECT name FROM table WHERE uid = " + uid;
  var name = null;
  db.all(query, function (err, rows) {
    if(err){
        console.log(err);
    }else{
      name = rows[0].name;
    }
  });
  return name; <--- this can be execute before db.all() if executed therefore returning null. This is because javascript runs asynchronously.
}

数据库查询的结果需要在回调中传递，也可以保存在全局变量中.

The result from database query needs to be passed in a callback or it can be saved in a global variable.

function getName(uid, callback){
  var query = "SELECT name FROM table WHERE uid = " + uid;
  db.all(query, function (err, rows) {
    if(err){
        console.log(err);
    }else{
        callback(rows[0].name);
    }
  });
}

为了从另一个文件执行:

In order to execute from another file:

function print(name) {
  console.log(name);
}
var uid = req.session.user;
getName(uid, print);

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