Question

我正在尝试对未绑定的子文档进行排序。这是集合：

[
    {
        otherFields: {},
        visites: ["58d46ffbf1c383862cf5de4a", "58d46ffbf1c383862cf5de49"]
    }
]

这是聚合：

db.exps.aggregate([
    { "$match": {} },
    { "$project": { "visites": 1 } },
    { "$unwind": "$visites" },
    { "$sort": { "visites.formVersion": 1 } },
    { "$group": { "_id": null, "count": { "$sum": 1 }, "data": { "$push": "$visites" } } }
])

我意识到用子字段排序是没有意义的，因为visites字段只是一个id的数组。是否可以在聚合中填充它们，以便对它们进行排序？

nodejs人口之后的结果是：

{
    "count": 50,
    "data": [
        {
            "_id": "58d46ffbf1c383862cf5de4a",
            "formVersion": 4,
            "start": "2017-06-04T07:30:00.000Z",
            "end": "2017-06-04T08:30:00.000Z",
            "type": "assessor",
            "expedient": "58d46ffaf1c383862cf5de41",
            "user": "58d46ff8f1c383862cf5de3a",
            "__v": 0,
            "isDeleted": false,
            "lastModified": "2017-03-24T01:01:47.343Z",
            "created": "2017-03-24T01:01:47.330Z"
        },
        {
            "_id": "58d46ffbf1c383862cf5de49",
            "formVersion": 3,
            "start": "2017-06-03T07:30:00.000Z",
            "end": "2017-06-03T08:30:00.000Z",
            "type": "assessor",
            "expedient": "58d46ffaf1c383862cf5de41",
            "user": "58d46ff8f1c383862cf5de3a",
            "__v": 0,
            "isDeleted": false,
            "lastModified": "2017-03-24T01:01:47.341Z",
            "created": "2017-03-24T01:01:47.328Z"
        },

Answer 1

假设有两个集合coll1和coll2：

> db.coll1.find()

{
 "_id": ObjectId("58eecf2a11b7af6f560666d8"),
  "otherFields": {

 },
 "visites": [
   "58d46ffbf1c383862cf5de4a",
   "58d46ffbf1c383862cf5de49"
  ]
}
> db.coll2.find()
{
  "_id": "58d46ffbf1c383862cf5de4a",
  "formVersion": 4,
  "start": "2017-06-04T07:30:00.000Z",
  "end": "2017-06-04T08:30:00.000Z",
  "type": "assessor",
  "expedient": "58d46ffaf1c383862cf5de41",
  "user": "58d46ff8f1c383862cf5de3a",
  "__v": 0,
  "isDeleted": false,
  "lastModified": "2017-03-24T01:01:47.343Z",
  "created": "2017-03-24T01:01:47.330Z"
}
{
  "_id": "58d46ffbf1c383862cf5de49",
  "formVersion": 3,
  "start": "2017-06-03T07:30:00.000Z",
  "end": "2017-06-03T08:30:00.000Z",
  "type": "assessor",
  "expedient": "58d46ffaf1c383862cf5de41",
  "user": "58d46ff8f1c383862cf5de3a",
  "__v": 0,
  "isDeleted": false,
  "lastModified": "2017-03-24T01:01:47.341Z",
  "created": "2017-03-24T01:01:47.328Z"
}

如果您希望按以下方式排序： formVersion字段，一个可能的聚合管道解决方案可能是： db.coll1.aggregate（[

// left outer join from coll2 to coll1
{$lookup:{
    from:"coll2",
    localField:"visites",
    foreignField:"_id",
    as:"data"
}},

// unwind the resulting array
{$unwind:"$data"},

// sort the unwinded documents using the formVersion field
{$sort:{"_id":1 ,"data.formVersion": 1}},

// collect the results into an array
{$group:{"_id":null, data:{$push:"$data"}}}
])

管道的结果是：

 {
  "_id": null,
  "data": [
    {
      "_id": "58d46ffbf1c383862cf5de49",
      "formVersion": 3,
      "start": "2017-06-03T07:30:00.000Z",
      "end": "2017-06-03T08:30:00.000Z",
      "type": "assessor",
      "expedient": "58d46ffaf1c383862cf5de41",
      "user": "58d46ff8f1c383862cf5de3a",
      "__v": 0,
      "isDeleted": false,
      "lastModified": "2017-03-24T01:01:47.341Z",
      "created": "2017-03-24T01:01:47.328Z"
    },
    {
      "_id": "58d46ffbf1c383862cf5de4a",
      "formVersion": 4,
      "start": "2017-06-04T07:30:00.000Z",
      "end": "2017-06-04T08:30:00.000Z",
      "type": "assessor",
      "expedient": "58d46ffaf1c383862cf5de41",
      "user": "58d46ff8f1c383862cf5de3a",
      "__v": 0,
      "isDeleted": false,
      "lastModified": "2017-03-24T01:01:47.343Z",
      "created": "2017-03-24T01:01:47.330Z"
    }
  ]
}

请注意，自MongoDB 3.4起，$lookup阶段存在某些限制;例如，两个集合必须位于同一个数据库中，from参数不能是分片集合。有关详细信息，请参阅https://docs.mongodb.com/manual/reference/operator/aggregation/lookup/ 另请注意，最后一个$group阶段将产生一个文档，该文档将受MongoDB的16 MB文档大小限制的约束。如果您愿意，可以删除$group阶段并迭代$sort阶段返回的光标。

mongodb sort unopulated subdocument

1 个答案: