MongoDB分组依据，每个组有排序和限制[重复]

Question

例如，我有一个收藏：

{ "_id" : 1, "name" : "abc", "score" : 10 }
{ "_id" : 2, "name" : "abc", "score" : 15 }
{ "_id" : 3, "name" : "abc", "score" : 20 }
{ "_id" : 4, "name" : "xyz", "score" : 10 }
{ "_id" : 5, "name" : "xyz", "score" : 15 }
{ "_id" : 6, "name" : "xyz", "score" : 20 }

如何在MongoDB中进行查询以按name分组，然后按分数排序并以限制=2进行。我想得到这样的：

    {"_id": "abc", "items": [
          { "_id" : 3, "name" : "abc", "score" : 20 },
          { "_id" : 2, "name" : "abc", "score" : 15 }]
    }
    {"_id": "xyz", "items": [
          { "_id" : 6, "name" : "xyz", "score" : 20 },
          { "_id" : 5, "name" : "xyz", "score" : 15 }]
    }

Answer 1

我的解决办法是

db.collection.aggregate([
    {$sort:{name:-1, score:-1}},
    {$group:{_id:"$name",items:{$push:{score:"$score"}}}}, 
    {$project:{items:{$slice:["$items", 2]}}}])
.pretty()

退货

{
    "_id" : "abc",
    "items" : [
        {
            "score" : 20
        },
        {
            "score" : 15
        }
    ]
}
{
    "_id" : "xyz",
    "items" : [
        {
            "score" : 20
        },
        {
            "score" : 15
        }
    ]
}