为每个用户获取最后创建的对象？

时间：2022-05-04 20:13:42

I have a collection, say, "Things":

我有一个集合，比如，“东西”：

{ id: 1
    creator: 1
    created: Today }
{ id: 2
    creator: 2
    created: Today }
{ id: 3
    creator: 2
    created: Yesterday }

I'd like to create a query that'll return each Thing created by a set of users, but only their most recently created thing.

我想创建一个查询，它将返回由一组用户创建的每个Thing，但只返回他们最近创建的东西。

What would this look like? I can get search my collection with an array of creators and it works just fine - how can I also only get the most recently created object per user?

这会是什么样的？我可以使用一系列创建者搜索我的集合，它可以正常工作 - 我怎样才能获得每个用户最近创建的对象？

Thing.find({ _creator : { "$in" : creatorArray })...

1 个解决方案

#1

3  

You cannot find, sort and pick the most recent in just a single find() query. But you can do it using aggregation:

您只能在一个find（）查询中找不到，排序和选择最新的。但是你可以使用聚合来做到这一点：

  • Match all the records where the creator is amongst the one who we are looking for.
  • 匹配创建者所在的所有记录。
  • Sort the records in descending order based on the created field.
  • 根据创建的字段按降序对记录进行排序。
  • Group the documents based on the creator.
  • 根据创建者对文档进行分组。
  • Pick each creator's first document from the group, which will also be his latest.
  • 从群组中挑选每个创作者的第一个文档，这也是他的最新文档。
  • Project the required fields.
  • 投射必填字段。

snippet:

片段：

Thing.aggregate([
{$match:{"creator":{$in:[1,2]}}},
{$sort:{"created":-1}},
{$group:{"_id":"$creator","record":{$first:"$$ROOT"}}},
{$project:{"_id":0,
           "id":"$record.id",
           "creator":"$record.creator",
           "created":"$record.created"}}
], function(err,data){
   })

#1

3  

You cannot find, sort and pick the most recent in just a single find() query. But you can do it using aggregation:

您只能在一个find（）查询中找不到，排序和选择最新的。但是你可以使用聚合来做到这一点：

  • Match all the records where the creator is amongst the one who we are looking for.
  • 匹配创建者所在的所有记录。
  • Sort the records in descending order based on the created field.
  • 根据创建的字段按降序对记录进行排序。
  • Group the documents based on the creator.
  • 根据创建者对文档进行分组。
  • Pick each creator's first document from the group, which will also be his latest.
  • 从群组中挑选每个创作者的第一个文档，这也是他的最新文档。
  • Project the required fields.
  • 投射必填字段。

snippet:

片段：

Thing.aggregate([
{$match:{"creator":{$in:[1,2]}}},
{$sort:{"created":-1}},
{$group:{"_id":"$creator","record":{$first:"$$ROOT"}}},
{$project:{"_id":0,
           "id":"$record.id",
           "creator":"$record.creator",
           "created":"$record.created"}}
], function(err,data){
   })
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