Question

我根据时间范围在Firestore上有三个查询。（24,12和6小时）。我正在使用Promise.all并且它有效。从代码中可以看出，我通过使用返回快照的索引来访问每个查询的结果。我已经读过，无论完成顺序如何，返回的值都将按照传递的Promise的顺序排列。

现在，我希望能够将一个对象传递给Promise.all，因为我的查询数量对于我想做的事情是不可预测的，基本上，我将循环到多个车辆并构建每个相同的3个查询，我将在Promise.all上传递所有内容。当Promise.all返回时，我希望能够知道该快照适用于哪个车辆和时间范围。

因此，我希望将此参数传递给Promise.all而不是数组。

{"vehicle1_24":query, "vehicle1_12":query, "vehicle1_6":query,
"vehicle2_24":query, "vehicle2_12":query, "vehicle2_6":query}

码

var queries = [
        vehicleRef.collection('telemetry').where('time_stamp', '<', today).where('time_stamp', '>', yesterday).get(),
        vehicleRef.collection('telemetry').where('time_stamp', '<', today).where('time_stamp', '>', twelveHours).get(),
        vehicleRef.collection('telemetry').where('time_stamp', '<', today).where('time_stamp', '>', sixHours).get()
      ]

      for (var i = 0; i < queries.length; i++) {
        queryResults.push(
          queries[i]
        )
      }

      Promise.all(queryResults)
        .then(snapShot=> {

          const yesterdayResult = result => getEnergy(result);
          const twelveHourResult = result => getEnergy(result);
          const sixHourResult = result => getEnergy(result);

          allYesterdayResult += yesterdayResult(snapShot[0])
          allTwelveHourResult += twelveHourResult(snapShot[1])
          allSixHourResult +=sixHourResult(snapShot[2])


          console.log("Done updating vehicle ", vehicle)
          // return res.send({"Result" : "Successful!"})
        }).catch(reason => {
          console.log(reason)
          // return res.send({"Result" : "Error!"})

Answer 1

此功能本身并不存在，但应该相当容易编写，与

一致

async function promiseAllObject(obj) {
  // Convert the object into an array of Promise<{ key: ..., value: ... }>
  const keyValuePromisePairs = Object.entries(obj).map(([key, valuePromise]) =>
    valuePromise.then(value => ({ key, value }))
  );

  // Awaits on all the promises, getting an array of { key: ..., value: ... }
  const keyValuePairs = await Promise.all(keyValuePromisePairs);

  // Turn it back into an object.
  return keyValuePairs.reduce(
    (result, { key, value }) => ({ ...result, [key]: value }),
    {}
  );
}

promiseAllObject({ foo: Promise.resolve(42), bar: Promise.resolve(true) })
  .then(console.log); // { foo: 42, bar: true }

Answer 2

您可以使用以下代码将对象转换为您将传递给Promise.all（）的数组

var queriesObject = {"vehicle1_24":query, "vehicle1_12":query, "vehicle1_6":query, "vehicle2_24":query, "vehicle2_12":query, "vehicle2_6":query};
//Of course, queriesObject can be an oject with any number of elements 


var queries = [];

for (var key in queriesObject) {
    if (queriesObject.hasOwnProperty(key)) {
        queries.push(queriesObject[key]);
    }
}

Promise.all(queries);

您将在与查询数组相对应的履行值的数组中收到Promise.all的结果，请参阅：Promise.all: Order of resolved values和https://www.w3.org/2001/tag/doc/promises-guide#aggregating-promises < / p>

将对象参数传递给Promise.all

2 个答案: