MongoDB：获取具有两个值的不同组合的最新文档

Question

所以我有一个问题，如何对数据库形成一个稍微复杂一点的特定查询。我有一个包含类似文件的集合：

[{
  "_id": { "$oid" : "Object1" },
  "created": { "$date" : "2021-11-14T10:58:01.456Z" },
  "primaryId": "SomeId1",
  "secondaryIdx": 0,
  "otherData" : something
}
{
  "_id": { "$oid" : "Object2" },
  "created": { "$date" : "2021-11-13T10:58:01.456Z" },
  "primaryId": "SomeId2",
  "secondaryIdx": 0,
  "otherData" : something
}
{
  "_id": { "$oid" : "Object3" },
  "created": { "$date" : "2021-11-15T10:58:01.456Z" },
  "primaryId": "SomeId2",
  "secondaryIdx": 1,
  "otherData" : something
}
{
  "_id": { "$oid" : "Object4" },
  "created": { "$date" : "2021-11-16T10:58:01.456Z" },
  "primaryId": "SomeId1",
  "secondaryIdx": 0,
  "otherData" : something
}]

而且我生成的集合应该只包含具有 primaryId + secondaryIdx 的唯一组合的文档。只要有超过一个文件的这种组合，我只想得到最新的一个。所以我的结果应该是这样的：

{
  "_id": { "$oid" : "Object2" },
  "created": { "$date" : "2021-11-13T10:58:01.456Z" },
  "primaryId": "SomeId2",
  "secondaryIdx": 0,
  "otherData" : something
}
{
  "_id": { "$oid" : "Object3" },
  "created": { "$date" : "2021-11-15T10:58:01.456Z" },
  "primaryId": "SomeId2",
  "secondaryIdx": 1,
  "otherData" : something
}
{
  "_id": { "$oid" : "Object4" },
  "created": { "$date" : "2021-11-16T10:58:01.456Z" },
  "primaryId": "SomeId1",
  "secondaryIdx": 0,
  "otherData" : something
}]

所以 Object1 被排除在结果之外，因为 primaryId+secondaryIdx 重复，而 Object4 较新。

我目前在我的应用程序中实现了此功能，但我认为在查询级别执行此操作会更好，因此我的应用程序不必加载不必要的大集合，然后可能会过滤掉大部分无论如何，他们立即。

Answer 1

您可以先$sort primaryId: 1, secondaryIdx: 1, created: -1。然后通过primaryId + secondaryIdx做一个$group然后取第一个文件。

db.collection.aggregate([
  {
    $sort: {
      primaryId: 1,
      secondaryIdx: 1,
      created: -1
    }
  },
  {
    $group: {
      _id: {
        primaryId: "$primaryId",
        secondaryIdx: "$secondaryIdx"
      },
      lastDoc: {
        $first: "$$ROOT"
      }
    }
  },
  {
    "$replaceRoot": {
      "newRoot": "$lastDoc"
    }
  }
])

这里是Mongo playground供您参考。

MongoDB：获取具有两个值的不同组合的最新文档

MongoDB: Get newest documents with distinct combination of two values

mongodb

mongodb-query

aggregation-framework

spring-data-mongodb