mongodb

MongoDB find and return all with max value

由 孤者浪人 提交于 2021-02-20 18:07:25
问题 I'm trying to get a list of documents that have the max value. I can specify it if I know the number of documents with max value (like in the solution in this another stackoverflow solution 'mongodb how to get max value from collections'), but I don't know how to do it if I don't know what the number of documents is. For example, using the following documents: {name:"a", age:10} {name:"b", age:11} {name:"d", age:12} {name:"c", age:12} So I know that there are 2 documents with max age of 12.

MongoDB find and return all with max value

由 ﹥＞﹥吖頭↗ 提交于 2021-02-20 18:05:43
问题 I'm trying to get a list of documents that have the max value. I can specify it if I know the number of documents with max value (like in the solution in this another stackoverflow solution 'mongodb how to get max value from collections'), but I don't know how to do it if I don't know what the number of documents is. For example, using the following documents: {name:"a", age:10} {name:"b", age:11} {name:"d", age:12} {name:"c", age:12} So I know that there are 2 documents with max age of 12.

仅使用CSS就可以提高页面渲染速度的4个技巧

由 随声附和 提交于 2021-02-20 16:16:19
文末福利资源更新 本文将重点介绍4个可以用来提高页面渲染速度的CSS技巧。 1. Content-visibility 一般来说，大多数Web应用都有复杂的UI元素，它的扩展范围超出了用户在浏览器视图中看到的内容。在这种情况下，我们可以使用内容可见性（ content-visibility ）来跳过屏幕外内容的渲染。如果你有大量的离屏内容，这将大大减少页面渲染时间。 这个功能是最新增加的功能之一，也是对提高渲染性能影响最大的功能之一。虽然 content-visibility 接受几个值，但我们可以在元素上使用 content-visibility: auto; 来获得直接的性能提升。 让我们考虑一下下面的页面，其中包含许多不同信息的卡片。虽然大约有12张卡适合屏幕，但列表中大约有375张卡。正如你所看到的，浏览器用了1037ms来渲染这个页面 。 下一步，您可以向所有卡添加 content-visibility 。 在这个例子中，在页面中加入 content-visibility 后，渲染时间下降到150ms，这是6倍以上的性能提升。 正如你所看到的，内容可见性是相当强大的，对提高页面渲染时间非常有用。根据我们目前所讨论的东西，你一定是把它当成了页面渲染的银弹。 content-visibility 的限制 然而，有几个领域的内容可视性不佳。我想强调两点，供大家参考。

windows 下安装MongoDB

由 南楼画角 提交于 2021-02-20 11:52:10
一：下载mongodb安装包 下载地址： https://www.mongodb.com/download-center/community 这里推荐下载msi的安装包 二：安装mongodb 双击下载下来的mongodb安装包进行安装 在Windows下安装软件十分的简单，只需要next就可以了，只需要注意点下面两点 1：如下图安装界面中选择自定义安装，这里可以选择您的安装目录，这里我选择的安装目录为：D:\MongoDB 2：取消如下图形界面管理工具勾选，勾选的话安装会十分十分的慢，如果您想要安装的话可以访问： https://www.mongodb.com/download-center/compass 进行下载安装 如下是mongodb安装后的目录结构 三：mongodb配置 安装号mongodb之后我们需要进行mongodb配置 1：启动mongodb服务 使用命令行进入mongodb安装目录的bin目录下执行 mongod --dbpath " D:\MongoDB\data " #D:\MongoDB\data为我安装的mongodb目录下的data目录，用户存储数据 运行如上名利之后在浏览器上访问：localhost:27017（27017为mongodb的默认端口号） 2：配置本地windows mongodb服务 1：在安装的根目录下新建一个mongod

《万亿级数据库MongoDB集群性能数十倍提升优化实践》核心17问详细解答

由 好久不见. 提交于 2021-02-20 10:33:09
《万亿级数据库MongoDB集群性能数十倍提升优化实践》核心17问详细解答 说明： 为了更好的理解背景，请提前阅读oschina分享的 《万亿级数据库MongoDB集群性能数十倍提升及机房多活容灾实践》 一文。 本文是2020年深圳Qcon全球软件开发大会 《专题：现代数据架构》 专场 、 dbaplus专场：万亿级数据库MongoDB集群性能优化实践 、mongodb2020年终盛会 分享 后，获得一致好评。本文收集了会后众多mongodb用户提的比较频繁的17个问题，并对每个问题进行了详细解答，一并整理到本文中。 分享内容回顾如下： MongoDB在OPPO互联网推广经验分享-如何把一个淘汰边缘的数据库逐步变为公司主流数据库 谈谈当前国内对MongoDB误解（丢数据、不安全、难维护）？ MongoDB跨机房多活方案-实现成本、性能、一致性"三丰收" MongoDB线程模型瓶颈及其优化方法 并行迁移：MongoDB内核扩容迁移速率数倍/数十倍提升优化实践 百万级高并发读写/千亿级数据量MongoDB集群性能数倍提升优化实践 万亿级数据量MongoDB集群性能数十倍提升优化实践 磁盘80%节省-记某服务接口千亿级数据迁移MongoDB，近百台SSD服务器节省原理 关于作者 前滴滴出行技术专家，现任OPPO文档数据库mongodb负责人

MongoDB select distinct and where

由 心不动则不痛 提交于 2021-02-20 10:17:23
问题 So I'm doing a select distinct which works, but I also want to add another key. $data = $this->db->command(array("distinct" => "scores","key"=>"target_user")); I need something like this: SELECT DISTINCT target_user FROM scores where seen = 1 Can it be done in mongo? 回答1: You can do it as follows by using distinct query : db.scores.distinct("target_user", {"seen":1}) Running distinct query using Aggregate Framework is shown below. Inserted following records into MongoDB. db.scores.insert(

MongoDB select distinct and where

由 旧城冷巷雨未停 提交于 2021-02-20 10:16:56
问题 So I'm doing a select distinct which works, but I also want to add another key. $data = $this->db->command(array("distinct" => "scores","key"=>"target_user")); I need something like this: SELECT DISTINCT target_user FROM scores where seen = 1 Can it be done in mongo? 回答1: You can do it as follows by using distinct query : db.scores.distinct("target_user", {"seen":1}) Running distinct query using Aggregate Framework is shown below. Inserted following records into MongoDB. db.scores.insert(

In mongoose, what is the difference between save(), insertOne() and updateOne(),when I want to add something new to a field that is already made?

由 半腔热情 提交于 2021-02-20 04:13:06
问题 for example I have a schema const listSchema=new mongoose.Schema({ name:String, items:Array }); const List=mongoose.model("List",listSchema); and I made a document const list=New List({ name: "list1", items:[item1, item2,item3] }); and then later I wanted to add a new item called item 4 so I used List.findOne({name:list1},function(err,foundList){ foundList.items.push(item4); foundList.save(); I know it might be a stupid question but it's confusing me. When I use .push I essentially added a

In mongoose, what is the difference between save(), insertOne() and updateOne(),when I want to add something new to a field that is already made?

由 主宰稳场 提交于 2021-02-20 04:12:26
问题 for example I have a schema const listSchema=new mongoose.Schema({ name:String, items:Array }); const List=mongoose.model("List",listSchema); and I made a document const list=New List({ name: "list1", items:[item1, item2,item3] }); and then later I wanted to add a new item called item 4 so I used List.findOne({name:list1},function(err,foundList){ foundList.items.push(item4); foundList.save(); I know it might be a stupid question but it's confusing me. When I use .push I essentially added a

In mongoose, what is the difference between save(), insertOne() and updateOne(),when I want to add something new to a field that is already made?

由 ぃ、小莉子 提交于 2021-02-20 04:11:00
问题 for example I have a schema const listSchema=new mongoose.Schema({ name:String, items:Array }); const List=mongoose.model("List",listSchema); and I made a document const list=New List({ name: "list1", items:[item1, item2,item3] }); and then later I wanted to add a new item called item 4 so I used List.findOne({name:list1},function(err,foundList){ foundList.items.push(item4); foundList.save(); I know it might be a stupid question but it's confusing me. When I use .push I essentially added a
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