$concat 字段与 $map mongodb 中的索引？ [复制]

我有以下收藏

{
    "_id" : ObjectId("5b16405a8832711234bcfae7"),
    "createdAt" : ISODate("2018-06-05T07:48:45.248Z"),
    "firstName": "Bruce",
    "lastName": "Wayne"
},
{
    "_id" : ObjectId("5b16405a8832711234bcfae8"),
    "createdAt" : ISODate("2018-06-05T07:48:45.248Z"),
    "firstName": "Clerk",
    "lastName": "Kent"
},
{
    "_id" : ObjectId("5b16405a8832711234bcfae9"),
    "createdAt" : ISODate("2018-06-05T07:48:45.248Z"),
    "firstName": "Peter",
    "lastName": "Parker"
}

我需要$project又一个关键索引$concat'INV-00' + 根元素的索引

我的输出应该是这样的

{
    "_id" : ObjectId("5b16405a8832711234bcfae7"),
    "createdAt" : ISODate("2018-06-05T07:48:45.248Z"),
    "firstName": "Bruce",
    "lastName": "Wayne",
    "index": "INV-001"
},
{
    "_id" : ObjectId("5b16405a8832711234bcfae8"),
    "createdAt" : ISODate("2018-06-05T07:48:45.248Z"),
    "firstName": "Clerk",
    "lastName": "Kent",
    "index": "INV-002"
},
{
    "_id" : ObjectId("5b16405a8832711234bcfae9"),
    "createdAt" : ISODate("2018-06-05T07:48:45.248Z"),
    "firstName": "Peter",
    "lastName": "Parker",
    "index": "INV-003"
}

我可以改变吗createdAt格式为这个Thu Jan 18 2018 using $dateToString或者是其他东西？？？

提前致谢！！！

虽然我当然建议您在客户端而不是在 MongoDB 内部执行此操作，但您可以通过以下方式获得您想要的东西 - 非常暴力但有效：

db.collection.aggregate([
    // you should add a $sort stage here to make sure you get the right indexes
{
    $group: {
        _id: null, // group all documents into the same bucket
        docs: { $push: "$$ROOT" } // just to create an array of all documents
    }
}, {
    $project: {
        docs: { // transform the "docs" field
            $map: { // into something
                input: { $range: [ 0, { $size: "$docs" } ] }, // an array from 0 to n - 1 where n is the number of documents
                as: "this", // which shall be accessible using "$$this"
                in: {
                    $mergeObjects: [ // we join two documents
                        { $arrayElemAt: [ "$docs", "$$this" ] }, // one is the nth document in our "docs" array
                        { "index": { $concat: [ 'INV-00', { $substr: [ { $add: [ "$$this", 1 ] }, 0, -1 ] } ] } } // and the second document is the one with our "index" field
                    ]
                }
            }
        }
    }
}, {
    $unwind: "$docs" // flatten the result structure
}, {
    $replaceRoot: {
        newRoot: "$docs" // restore the original document structure
    }
}])