无法等待 sqlite3.Node.js 中的 Database.get() 函数完成

Question

我正在使用node-sqlite3在node.js中遇到一些基本的async/await问题。
我的目标是从SQLite DB中选择一些值，检查它是否有某些条件，并在满足条件时采取一些操作。代码如下：

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

正如我们所看到的，我们从 orderAlreadyProcessing 返回太早，返回值 = 'undefined'。因此，满足条件，执行操作，然后 Database.get(( 返回。但是，如果适当地等待，条件将得不到满足。

如何让它等待结果值？

Answer 1

由于你想使用async/await

，而 node-sqlite3(sqlite3( 库不支持 Promise API，你需要使用 node-sqlite (sqlite( 库，它是sqlite3的包装器，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();

我特别没有删除您的控制台.log和代码的其他部分，以免混淆程序的原始逻辑。

Answer 2

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

注意：下面是INSERT/run的示例，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 });