无法在 Node.js 中等待 sqlite3.Database.get() 函数完成

Question

我正在使用 node-sqlite3 在 node.js 中解决一些基本的异步/等待问题。
我的目标是从 SQLite DB 中选择一些值，检查它的某些条件并在满足条件时采取一些措施。这是代码：

const sqlite3 = require('sqlite3').verbose();
main();

async function main() {
    let ordersDb = await createDbConnection('./ProcessedOrders.db');
    var orderProcessed = await orderAlreadyProcessed(ordersDb, "555");
    console.log("orderProcessed = " + orderProcessed);
    if (!orderProcessed) {
        console.log("So condition is met!");
    }
}


async function orderAlreadyProcessed(ordersDb, orderNumberStr) {
    console.log('starting orderAlreadyProcessed function'); //DEBUG
    var result;
    var query = 'select count(SoldOrderNumber) as "recsCount" from ProcessedSoldOrders where SoldOrderNumber = ?;';
    await ordersDb.get(query
    ,[orderNumberStr]
    ,(err, row) => {
        console.log('Row with count = ' + row); //DEBUG
        console.log('row.recsCount = ' + row.recsCount); //DEBUG
        result = typeof row !== 'undefined' && row.recsCount > 0;
    });
    console.log('Returning ' + result); //DEBUG
    return result;
}

async function createDbConnection(dbFileName) {
    let db = new sqlite3.Database(dbFileName, (err) => {
        if (err) {
            console.log(err.message);
        }
    });
    return db;
}

但是我得到的是进一步执行的代码，根本不需要等待 Database.get() 方法！结果，这是我在控制台中看到的打印内容：

starting orderAlreadyProcessed function
Returning undefined
orderProcessed = undefined
So IF condition met!
Row with count = [object Object]
row.recsCount = 1

正如我们所见，我们过早地从 orderAlreadyProcessed 返回，返回值 = 'undefined'。所以条件满足，采取行动，然后 Database.get() 返回。但如果它被适当地等待，条件将不会满足。

我怎样才能让它等待结果值？

Answer 1

如果我们不使用另一个库
，那么我们可以返回一个new Promise函数 & use await，如下所示：

注意：下面有 , 的示例INSERT/run，而不是SELECT/get，但promise/await工作原理相同

const sqlite3 = require("sqlite3").verbose();

let db;
db = new sqlite3.Database('./Chinook.db');

function insert() {
  return new Promise((resolve, reject) => {          // return new Promise here <---
    const userId = uuid4();

    let sql = `INSERT INTO Users(id) VALUES (?)`;    // INSERT <----
    let params = [userId];

    return db.run(sql, params, function (err, res) { // .run <----
      if (err) {
        console.error("DB Error: Insert failed: ", err.message);
        return reject(err.message);
      }
      return resolve("done");
    });
  });
}

let result = await insert();                       // now await works fine <------
res.send({ result });

Answer 2

既然要使用async/await，而node-sqlite3(sqlite3)库不支持Promise API，就需要使用node-sqlite(sqlite)库，它是sqlite3对Promise API的封装，增加了对Promise API的支持。然后，您的代码将如下所示：

const sqlite3 = require('sqlite3');
const { open } = require('sqlite');

async function main() {
    try {
        sqlite3.verbose();
        const ordersDb = await createDbConnection('./ProcessedOrders.db');
        const orderProcessed = await orderAlreadyProcessed(ordersDb, "555");
        console.log("orderProcessed = " + orderProcessed);
        if (!orderProcessed) {
            console.log("So condition is met!");
        }
    } catch (error) {
        console.error(error);
    }
}


async function orderAlreadyProcessed(ordersDb, orderNumberStr) {
    try {
        console.log('Starting orderAlreadyProcessed function');
        const query = 'SELECT COUNT(SoldOrderNumber) as `recsCount` from ProcessedSoldOrders where SoldOrderNumber = ?;'
        const row = await ordersDb.get(query, [orderNumberStr]);
        console.log('Row with count =', row);
        console.log('row.recsCount =', row.recsCount);
        const result = typeof row !== 'undefined' && row.recsCount > 0;
        console.log('Returning ' + result);
        return result;
    } catch (error) {
        console.error(error);
        throw error;
    }
}

function createDbConnection(filename) {
    return open({
        filename,
        driver: sqlite3.Database
    });
}

main();

我特意没有把你的console.log等部分代码去掉，以免混淆你程序的原始逻辑。