[英]Node.js Promise.all when function returns nothing
How to handle multiple calls to the same function when its returning nothing. 什么也不返回时如何处理对同一函数的多次调用。 I need to wait untill all calls are finished so i can call another function.
我需要等到所有调用完成后才能调用另一个函数。
For now I'm using Promise.all()
but it doesn't seem right: 现在,我正在使用
Promise.all()
但它似乎不正确:
Promise.all(table_statements.map(i => insertValues(i)))
.then(function(result) {
readNodeData(session, nodes);
})
.catch(function() {
console.log(err);
})
function insertValues(statement) {
return new Promise((res, rej) => {
database.query(statement, function (err, result) {
if (err) {
rej(err)
}
else{
console.log("Daten in Tabelle geschrieben")
res(); // basically returning nothing
}
});
});
}
This writes data to a database in multiple statements, i need to wait untill all are finished. 这会以多条语句将数据写入数据库,我需要等到所有操作完成后再进行操作。 Is this actually the "right" way to do it?
这实际上是“正确”的方法吗? I mean... it works, but i have the feeling it's not how you are supposed to do it.
我的意思是...它起作用了,但是我感觉这不是您应该怎么做。
Using Promise.all
for your case is a good call, since it returns a Promise, when all the promises passed as an iterable are resolved. 在您的案例中使用
Promise.all
是一个很好的选择,因为当所有作为迭代对象传递的promise被解决时,它会返回Promise。 See the docs . 请参阅文档 。
However, for brevity and readability, try converting your insertValues
into async-await
function as follows. 但是,为简洁起见,请尝试按以下方式将
insertValues
转换为async-await
函数。 This tutorial would be a great place to start learning about async functions in JavaScript. 本教程是开始学习JavaScript异步功能的好地方。
// async insertValues function - for re-usability (and perhaps easy unit testing),
// I've passed the database as an argument to the function
async function insertValues(database, statement) {
try {
await database.query(statement);
} catch (error) {
console.error(error);
}
}
// using the insertValues() function
async function updateDatabase(database) {
try {
// I am using 'await' here to get the resolved value.
// I'm not sure this is the direction you want to take.
const results = await Promise.all(
tableStatements.map(statement => insertValues(database, statement))
);
// do stuff with 'results'.. I'm just going to log them to the console
console.log(results);
} catch (error) {
console.error(error);
}
}
Here, insertValues()
function doesn't return any value. 在此,
insertValues()
函数不会返回任何值。 Its operation on the database is entirely dependent on the query statement passed to it. 它对数据库的操作完全取决于传递给它的查询语句。 I wrapped it within a
try-catch
block so as to catch any errors that might arise while performing the operation (s) above. 我将其包装在
try-catch
块中,以捕获执行上述操作时可能出现的任何错误。 More details on handling errors using try-catch
can be found here . 可以在此处找到有关使用
try-catch
处理错误的更多详细信息。
Your promisified write to database looks ok, so we can update code from another part. 您向数据库承诺的写入看起来不错,因此我们可以从另一部分更新代码。
Let's rewrite it a little to use async/await
and try/catch
. 让我们用
async/await
和try/catch
重写一下。
(async() => {
const promisifiedStatements = table_statements.map(i => insertValues(i));
try {
await Promise.all(promisifiedStatements);
readNodeData(session, nodes);
} catch(e){
console.log(e)
}
})();
I use here IIFE to use await
behaviour. 我在这里使用IIFE来使用
await
行为。
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