是否可以在MongoDB中的$ cond中编写正则表达式

本文介绍了是否可以在MongoDB中的$ cond中编写正则表达式的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我需要使用$ cond合并differnetnet列，而我需要编写的一个$ cond如下:

I need to use $cond to combine differenet column, and one $cond I need to write is as following:

create_widget: { $sum:{ $cond:[{$and: [ {$eq: ['$Method', 'POST']}, {Url:{$regex: /.*\/widgets$/}} ]}, 1, 0] } }

这段代码似乎不正确，正则表达式不能放在这里.还有其他方法吗?我想匹配Url和正则表达式，并将代码放在$ cond下.

and this code is not right, it seems, regular expression can not be put here.Is there any other way to do this? I want to match Url and regular expression and put the code under $cond.

样本数据显示为

{"BrandId":"a","SessionId":"a1","Method":"POST","Url":"/sample/widgets"} {"BrandId":"a","SessionId":"a2","Method":"POST","Url":"/sample/blog"} {"BrandId":"b","SessionId":"b1","Method":"PUT","Url":"/sample/widgets"}

我编写的整个代码如下:

The whole code I wrote is as following:

db.tmpAll.aggregate([ {$group: { _id: {BrandId:'$BrandId'}, SessionId: {$addToSet: '$SessionId'}, create_widget: { $sum:{ $cond:[{$and: [ {$eq: ['$Method', 'POST']}, {} ]}, 1, 0] } } }}, {$group: { _id: '$_id.BrandId', distinct_session: {$sum: {$size: '$SessionId'}}, create_widget: {$sum: '$create_widget'} }} ]);

示例代码的预期结果是

{ "_id" : "a", "distinct_session" : 2, "create_widget" : 1 } { "_id" : "b", "distinct_session" : 1, "create_widget" : 0 }

推荐答案

对于 MongoDB 4.2 和较新的生产版本，以及在4.1.11和较新的开发版本中，使用 $regexMatch ，它是 $regexFind ，可用于正则表达式匹配和捕获.

For MongoDB 4.2 and newer production releases, and in the 4.1.11 and newer development versions, use $regexMatch which is a syntactic sugar on top of $regexFind which can be used for regex matching and capturing.

db.tmpAll.aggregate([ { "$group": { "_id": { "BrandId": "$BrandId", "SessionId": "$SessionId" }, "widget_count": { "$sum": { "$cond": [ { "$and": [ { "$eq": ["$Method", "POST"] }, { "$regexMatch": { "input": "$Url", "regex": /widget/ } } ] }, 1, 0 ] } }, "session_count": { "$sum": 1 } } }, { "$group": { "_id": "$_id.BrandId", "create_widget": { "$sum": "$widget_count" }, "distinct_session": { "$sum": "$session_count" } } } ]);

此 SERVER-8892-使用中，JIRA尚未解决$regex作为$cond 中的表达式.但是，作为解决方法，对于不具有上述功能的MongoDB较早版本，请在聚合管道中使用以下解决方法.

There is an open JIRA issue for this SERVER-8892 - Use $regex as the expression in a $cond. However, as a workaround, For older MongoDB versions which do not have the above features, use the following workaround in your aggregation pipeline.

它使用> $substr 运算符，位于 $project 运算符阶段提取URL的一部分，并作为正则表达式的变通方法. :

It uses the $substr operator in the $project operator stage to extract the part of the URL and acts as a workaround for the regex. :

db.tmpAll.aggregate([ { "$group": { "_id": { "BrandId": "$BrandId", "SessionId": "$SessionId" }, "widget_count": { "$sum": { "$cond": [ { "$and": [ { "$eq": ["$Method", "POST"] }, { "$eq": [ { "$substr": [ "$Url", 8, -1 ] }, "widget"] } ] }, 1, 0 ] } }, "session_count": { "$sum": 1 } } }, { "$group": { "_id": "$_id.BrandId", "create_widget": { "$sum": "$widget_count" }, "distinct_session": { "$sum": "$session_count" } } } ]);

输出

/* 1 */ { "result" : [ { "_id" : "a", "create_widget" : 1, "distinct_session" : 2 }, { "_id" : "b", "create_widget" : 0, "distinct_session" : 1 } ], "ok" : 1 }