无法在Node.js上使用sqlite3将行放入数组中 [英] Can't put rows into array using sqlite3 on Node.js

问题描述

我在Node.js中有一个代码，可以从SQLite数据库中选择所有内容并打印每一行，并且它行得通，这是代码:

I have a code in Node.js that selects everything from a SQLite Database and print every row and it works, here's the code:

var sqlite3=require('sqlite3').verbose();

var db=new sqlite3.Database('./database.db',(err)=>{
    if(err){
        return console.error(err.message);
    }
    console.log('Connected...');
});

db.all('SELECT * FROM langs ORDER BY name',[],(err,rows)=>{
    if(err){
        return console.error(err.message);
    }
    rows.forEach((row)=>{
        console.log(row.name);
    });
});

db.close((err) => {
    if (err) {
        return console.error(err.message);
    }
    console.log('Database closed...');
});

它打印:

Connected...
C
Java
Database closed...

但是当我尝试使用此方法将行放入数组中时，它不起作用:

But when I try using this to get the rows into an array, it doesnt work:

var data=[];
db.all('SELECT * FROM langs ORDER BY name',[],(err,rows)=>{
    if(err){
        return console.error(err.message);
    }
    rows.forEach((row)=>{
        data.push(row);
    });
});

for(col in data){
    console.log(col.name);
}

它打印:

Connected...
Database closed...

解决方案:修改代码以使其与 async/await 一起使用并将Node更新到版本8.11.1后，它可以工作，代码:

SOLUTION: After modifying the code to work with async/await and updating Node to version 8.11.1, it works, code:

var data=[],records=[];

function getRecords(){
    return new Promise(resolve=>{
        db.all('SELECT * FROM langs ORDER BY name',[],(err,rows)=>{
            if(err){
                return console.error(err.message);
            }
            rows.forEach((row)=>{
                data.push(row);
            });

            resolve(data);
        });
    });
}

async function asyncCall(){
    records=await getRecords();

    records.forEach(e=>{
        console.log(e.name);
    });
}

asyncCall();

推荐答案

这是因为 db.all 是异步.数据数组尚未填充，您正在尝试遍历它.只需将 for 循环移到内部，就可以完成.

This is because db.all is asynchronous. Data array is not yet populated and you are trying to loop through it. Just move for loop inside and you're done.

您的最终代码应为

var data=[],
     records = [];
function getRecords(){
  return new Promise((resolve,reject)=>{
  db.all('SELECT * FROM langs ORDER BY name',[],(err,rows)=>{
    if(err){
        return console.error(err.message);
    }
    rows.forEach((row)=>{
        data.push(row);
    });
    
   resolve(data);
})
  
  })
}

(async function(){
  records = await getRecords();
})()

ps.使用 for(.. in ..)不是一个好主意，最好使用 forEach

ps. It is not good idea to use for(..in..) you better use forEach

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