未加星标

Query on string length in MongoDB

字体大小 | |
[前端(javascript) 所属分类 前端(javascript) | 发布者 店小二04 | 时间 2016 | 作者 红领巾 ] 0人收藏点击收藏

If you need to query on string length, you will need to use the $where operator. As per the documentation, you can pass either a string with a javascript expression or a JavaScript function.

The downside to this operation is that it operates on each document in the collection. As a result, it can be a slow. So use with caution.

For the examples below, lets consider a document with the following structure:

{ "username": "brian", "addresses': [ { "address": "500 Grant Street", "city": "Pittsburgh", "state": "PA", "zip": "15219", "country": "US" }, { "address": "405 Spray Ave", "city": "Banff", "state": "AB", "zip": "T1L1J4", "country": "CA" } ] } String Expressions

So first thing, here's a simple JS expression in a string:

db.users.find({ $where: 'this.username.length < 4' })

The above example will find all documents in the users collection that have a username property with a length less than 4 characters.

You'll notice that in the expression, the reference to the document is made with this .

The string expressions will work for property or sub-document access and is straightforward for simple queries.

Function Expressions

If you have to work with Arrays or more complicated queries across multiple properties, you will need to use the function based approach.

This is similar to the string based approach, except you pass in a function to execute for each document:

db.users.find({ $where: function() { for(var i = 0; i < this.addresses.length; i++) { var address = this.addresses[i]; if(address.state.length > 2) { return true; } } } });

The above function will iterate over the addresses array and look at the length of each . It will look at the state property of each address and see if the length is larger than 2 characters.

Conclusion

Hopefully this helps you understand how string queries work in MongoDB.

本文前端(javascript)相关术语:javascript是什么意思 javascript下载 javascript权威指南 javascript基础教程 javascript 正则表达式 javascript设计模式 javascript高级程序设计 精通javascript javascript教程

主题: MongoDBJavaScriptJava
分页:12
转载请注明
本文标题:Query on string length in MongoDB
本站链接:http://www.codesec.net/view/482655.html
分享请点击:


1.凡CodeSecTeam转载的文章,均出自其它媒体或其他官网介绍,目的在于传递更多的信息,并不代表本站赞同其观点和其真实性负责;
2.转载的文章仅代表原创作者观点,与本站无关。其原创性以及文中陈述文字和内容未经本站证实,本站对该文以及其中全部或者部分内容、文字的真实性、完整性、及时性,不作出任何保证或承若;
3.如本站转载稿涉及版权等问题,请作者及时联系本站,我们会及时处理。
登录后可拥有收藏文章、关注作者等权限...
技术大类 技术大类 | 前端(javascript) | 评论(0) | 阅读(27)