用于返回按单个字段分组的最新版本文档的mongoose查询

Question

我有这些文件，

{
    "_id" : 1,
    "fId" : "test",
    "pId" : "test",
    "url" : "A",
    "subfolder" : "a"
}

,
{
    "_id" : 3,
    "fId" : "test",
    "pId" : "test", 
    "url" : "A",
    "subfolder" : "b"
}

,
{
    "_id" : 5,
    "fId" : "test",
    "pId" : "test"
    "url" : "A",
    "subfolder" : "c"
}

,
{
    "_id" : 2,
    "fId" : "test",
    "pId" : "test",
    "url" : "B",
    "subfolder" : "a"
}

,
{
    "_id" : 4,
    "fId" : "test",
    "pId" : "test",
    "url" : "B",
    "subfolder" : "b"
}

,
{
    "_id" : 7,
    "fId" : "test",
    "pId" : "test",
    "url" : "A",
    "subfolder" : "d"
}

,
{
    "_id" : 8,
    "fId" : "test",
    "pId" : "test",
    "url" : "B",
    "subfolder" : "d"
}

,
{
    "_id" : 9,
    "fId" : "test",
    "pId" : "test",
    "url" : "A",
    "subfolder" : "e"
}

,
{
    "_id" : 10,
    "fId" : "test",
    "pId" : "test",
    "url" : "B",
    "subfolder" : "e"
}

,
{
    "_id" : 6,
    "fId" : "test",
    "pId" : "test",
    "url" : "B",
    "subfolder" : "c"
}

如何根据_id，group by子文件夹编写mongoose查询来对这些文档进行排序，并返回最近的5个组。

预期结果是

group 1:
[{
    "_id" : 10,
    "fId" : "test",
    "pId" : "test",
    "url" : "B",
    "subfolder" : "e"
},
{
    "_id" : 9,
    "fId" : "test",
    "pId" : "test",
    "url" : "A",
    "subfolder" : "e"
}]
,
group 2:
[{
    "_id" : 8,
    "fId" : "test",
    "pId" : "test",
    "url" : "B",
    "subfolder" : "d"
}
,
{
    "_id" : 7,
    "fId" : "test",
    "pId" : "test",
    "url" : "A",
    "subfolder" : "d"
}]
,

group 3:
[{
    "_id" : 6,
    "fId" : "test",
    "pId" : "test",
    "url" : "B",
    "subfolder" : "c"
}
,
{
    "_id" : 5,
    "fId" : "test",
    "pId" : "test"
    "url" : "A",
    "subfolder" : "c"
}]
,
group 4:
[{
    "_id" : 4,
    "fId" : "test",
    "pId" : "test",
    "url" : "B",
    "subfolder" : "b"
}
,
{
    "_id" : 3,
    "fId" : "test",
    "pId" : "test", 
    "url" : "A",
    "subfolder" : "b"
}]
,

group 5:
[{
    "_id" : 2,
    "fId" : "test",
    "pId" : "test",
    "url" : "B",
    "subfolder" : "a"
}
,
{
    "_id" : 1,
    "fId" : "test",
    "pId" : "test",
    "url" : "A",
    "subfolder" : "a"
}]

我尝试过查询

model.aggregate(
   [      
     {$match : {fId : "test" ,  pId : "test"}},
     {$group : {_id : "$subfolder", recording: { $push: "$$ROOT" } }},     
     {$skip : 5*(pageNumber-1)},
     {$sort : {"_id": -1}},    
     {$limit : 5 }
   ]
  )

我得到随机的5组，而不是最近的组，结果也没有根据_id进行排序。

Answer 1

你在这里误解了跳过和限制的使用。试试这个：

model.aggregate(
   [      
     {$match : {fId : "test" ,  pId : "test"}},
     {$group : {_id : "$subfolder", recording: { $push: "$$ROOT" } }},     
     {$sort : {"recording._id": -1}},
     {$limit: 5}
   ]
  )

提供示例文档的

输出：

       {
    "_id" : "5",
    "recording" : [
        {
            "_id" : 9,
            "fId" : "test",
            "pId" : "test",
            "url" : "A",
            "subfolder" : "5"
        },
        {
            "_id" : 10,
            "fId" : "test",
            "pId" : "test",
            "url" : "B",
            "subfolder" : "5"
        }
    ]
}
{
    "_id" : "4",
    "recording" : [
        {
            "_id" : 7,
            "fId" : "test",
            "pId" : "test",
            "url" : "A",
            "subfolder" : "4"
        },
        {
            "_id" : 8,
            "fId" : "test",
            "pId" : "test",
            "url" : "B",
            "subfolder" : "4"
        }
    ]
}
{
    "_id" : "3",
    "recording" : [
        {
            "_id" : 5,
            "fId" : "test",
            "pId" : "test",
            "url" : "A",
            "subfolder" : "3"
        },
        {
            "_id" : 6,
            "fId" : "test",
            "pId" : "test",
            "url" : "B",
            "subfolder" : "3"
        }
    ]
}
{
    "_id" : "2",
    "recording" : [
        {
            "_id" : 3,
            "fId" : "test",
            "pId" : "test",
            "url" : "A",
            "subfolder" : "2"
        },
        {
            "_id" : 4,
            "fId" : "test",
            "pId" : "test",
            "url" : "B",
            "subfolder" : "2"
        }
    ]
}
{
    "_id" : "1",
    "recording" : [
        {
            "_id" : 1,
            "fId" : "test",
            "pId" : "test",
            "url" : "A",
            "subfolder" : "1"
        },
        {
            "_id" : 2,
            "fId" : "test",
            "pId" : "test",
            "url" : "B",
            "subfolder" : "1"
        }
    ]
}