为什么即使在使用async等待多个呼叫后仍然得到空响应? [英] Why even after using async await for multiple calls still got empty response?

问题描述

这是调用异步api的简单节点路由.

Here is simple node route in which calling an asynchronous api.

循环后需要的是return data.但是它正在返回空白对象.

What needed is to return data after the looping. But It is returning blank object.

try {
  const array = ["brunch", "lunch", "crunch"]
  const data = {}
  array.map(async(d) => {
    const venue = await Venue.find({ "category": { "$in": [d] }})
    data[d] = venue
  })
  return data
} catch(err) {
  throw err
}

请帮助我实现这一目标

推荐答案

有一种更好的方法可以通过MongoDB获得所需的结果，而无需循环，请使用聚合框架，在该框架中，您可以运行以下使用的管道> $facet as

There is a better way to get the desired result with MongoDB and no need to loop, use the aggregation framework where you can run the following pipeline which uses $facet as

try {
    const array = ["brunch", "lunch", "crunch"]
    const facet = array.reduce((acc, cur) => {
        acc[cur] = [{ "$match": { "category": cur } }]
        return acc
    }, {})
    const pipeline = [
        { "$match": { "category": { "$in": array } } },
        { "$facet": facet }
    ]
    const results = await Venue.aggregate(pipeline).exec()
    const data = results[0]

    return data
} catch(err) {
    throw err
}

---

您还可以按类别键和 $push 每个组中的文档，然后将其转换为

---

You can also group the documents by the category key and $push the documents per group and then convert into keys of a document in a $replaceRoot with $arrayToObject

try {
    const array = ["brunch", "lunch", "crunch"]
    const pipeline = [
        { "$match": { "category": { "$in": array } } },
        { "$group": { 
            "_id": "$category",
            "data": { "$push": "$$ROOT" }
        } },
        { "$group": {
            "_id": null,
            "venues": {
                "$push": {
                    "k": "$_id",
                    "v": "$data"
                }
            } 
        } },
        { "$replaceRoot": {
            "newRoot": { "$arrayToObject": "$venues" }
        } }
    ]
    const results = await Venue.aggregate(pipeline).exec()
    const data = results[0]

    return data
} catch(err) {
    throw err
}

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