mongodb 获取最后插入的文档 [英] mongodb get last inserted document

问题描述

此 Meteor 代码尝试查找集合中的最后一个文档.

This Meteor code tries to find the last document in a collection.

.find({userId: this.userId}, {sort: {createdAt: -1}, limit: 1});

但是由于所有文档都是按时间顺序排列的，我想删除 createdAt 字段，所以一旦它被删除"，是否有一种不昂贵"的方法来返回最后输入的文档?谢谢

But since all the documents are in chronological order, I thought to remove the createdAt field, so once that is 'deleted', Is there a "not expensive" way to return just the last entered document? Thanks

{userId: 'someId', info: 'someInfo'}
myCol.findLast().info;              <--- my wish list

文档中的

$last(aggregation) 首先进行排序等等

$last(aggregation) in the docs first does sorting among other things

编辑
尝试利用斯蒂芬伍兹提出的想法；

edit
An attempt to utilise the idea given by Stephen Woods;

server.js

MyCol._ensureIndex({createdAt: -1});
MyCol.before.insert(function (userId, doc) {
  doc.userId = userId;
  createdAt = Date.now();
});
Meteor.publish('myCol', function () {
  return MyCol.findOne({userId: this.userId});
});

推荐答案

我将假设昂贵是指执行时间.在这种情况下，您需要 createdAt 字段、createdAt 上的二级索引，并使用 findOne() 语句.要在 createdAt 上为您的集合创建索引，请执行以下操作:

I'm going to make the assumption that by expensive you mean execution time. In that case, you want a createdAt field, a secondary index on createdAt, and to use a findOne() statement. To create the index on createdAt for your collection, do:

myCol._ensureIndex({ createdAt: -1 });

然后在您的发布中:

Meteor.publish('myCol', function () {
  return MyCol.find({userId: this.userId}, { sort: { createdAt: -1 } });
});

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