javascript - 如何从 Javascript 中的集合数组中提取键的值

Question

我想从一系列集合中获取数组中键的值。请找到代码片段和预期输出。我会如果您能帮助我了解应该进入聚合阶段以获得所需输出的内容，将不胜感激。请注意，将有超过 5000 个集合

db.collection1.insertMany([{
    item: "journal",
    qty: 25,
    tags: blank
  },
  {
    item: "mat",
    qty: 85,
    tags: gray
  },
  {
    item: "mousepad",
    qty: 25,
    tags: gel
  }
])

db.collection2.insertMany([{
    abc: "paplu",
    qiity: 01,
    thugs: red
  },
  {
    abc: "mat",
    qiity: 85,
    thugs: gray
  },
  {
    abc: "mousepad",
    qiity: 25,
    thugs: gel
  }
])

var a = ["collection1", "collection2"];


for (var i = 0; i < a.length; i++) {
db[a[i]].aggregate([])};



Expected Output:
collection1
{
item : ["journal","mat","mousepad"],
qty : [25,85,25],
tags : [blank,gray,gel]
}
collection2
{
abc : ["paplu","mat","mousepad"],
qiity : [01,85,25],
thugs : [red,gray, gel]
}





Please note, I'm trying to achieve this using MongoDB/JavaScript

It would be great if someone can help me with this!

Answer 1

您可以从 $objectToArray 开始将 ROOT 对象中的键放入数组中。然后你可以运行 $unwind和 $group通过 null 和 $addToSet从整个集合中获取包含唯一键名的单个文档。在最后一步中，您需要使用 $map 将数组转换回单个文档, $arrayToObject和 $replaceRoot :

db.collection.aggregate([
    {
        $project: { kv: { $objectToArray: "$$ROOT" } }
    },
    {   $unwind: "$kv" },
    {
        $group: {
            _id: null,
            keys: { $addToSet: "$kv.k" }
        }
    },
    {
        $replaceRoot: {
            newRoot: {
                $arrayToObject: {
                    $map: { input: "$keys", in: [ "$$this", 1 ] }
                }
            }
        }
    }
])

Mongo Playground