通过 java 驱动对 mogodb4.0 中的子文档进行排序

Question

我正在尝试按 Java 对子文档进行排序。我无法找到所需的输出。我的数据集是：

[
{
    "_id": {
        "$oid": "5b91668a0f77e30c11574c88"
    },
    "driverId": "22",
    "busId": "55",
    "startTime": {
        "$date": 1536255626852
    },
    "location": [
        {
            "latitude": 18.5803721,
            "longitude": 73.7447051,
            "position": 0,
            "status": 1,
            "time": {
                "$date": 1536255628848
            }
        },
        {
            "latitude": 18.5803721,
            "longitude": 73.7447051,
            "position": 1,
            "status": 2,
            "time": {
                "$date": 1536255656122
            }
        },
        {
            "latitude": 18.5803721,
            "longitude": 73.7447051,
            "position": 1,
            "status": 2,
            "time": {
                "$date": 1536255656167
            }
        }
    ]
},
{
    "_id": {
        "$oid": "5b8c2cc70f77e322617c1ba1"
    },
    "driverId": "22",
    "busId": "55",
    "startTime": {
        "$date": 1535913159533
    },
    "location": [
        {
            "latitude": 18.5804663,
            "longitude": 73.7447209,
            "position": 0,
            "status": 1,
            "time": {
                "$date": 1535913160226
            }
        },
        {
            "latitude": 18.5804663,
            "longitude": 73.7447209,
            "position": 1,
            "status": 2,
            "time": {
                "$date": 1535913186460
            }
        },
        {
            "latitude": 18.5804663,
            "longitude": 73.7447209,
            "position": 1,
            "status": 2,
            "time": {
                "$date": 1535913187603
            }
        }
    ]
}
]

还有我写的代码：

AggregateIterable<Document> findIterable = tripsCollection.aggregate(Arrays.asList(
            new Document("$match", new Document("busId", busId)),
            new Document("$sort", new Document("startTime", -1)),
            new Document("$sort", new Document("location.position", -1))));

当我按 _Id 或 startTime 对文档进行排序时，会相应地输出。但是当我尝试对子文档进行排序时，结果集不会改变。

我也尝试了其他一些变化：

Bson bsonFilterBus = Filters.eq("busId", busId);
Bson sortByDate = descending("startTime");
Bson sortByPosition = descending("location.position");
FindIterable<Document> findIterable = tripsCollection.find(bsonFilterBus).sort(sortByDate).sort(sortByPosition);

但结果是一样的。即不根据 location.position 排序

我正在使用 MongoDb 4.0。在我读到的某处，Mongo DB 没有提供任何对子文档进行排序的方法。请帮帮我。

Answer 1

您必须 $unwind 子文档，然后 $sort 通过位置的位置字段和 $group 以获取位置数组。

类似

AggregateIterable<Document> findIterable = tripsCollection.aggregate(
     Arrays.asList(
      new Document("$match", new Document("busId", busId)),
      new Document("$unwind", "$location"),
      new Document("$sort", new Document("location.position", -1)),
      new Document("$group", 
           new Document("_id", "$_id")
            .append("driverId", new Document("$first","$driverId"))
            .append("busId", new Document("$first","$busId"))
            .append("startTime", new Document("$first","$startTime"))
            .append("location", new Document("$push","$location"))
      ),
      new Document("$sort", new Document("startTime", -1))
   )
);