1.作用与语法描述
作用： 正则表达式是使用指定字符串来描述、匹配一系列符合某个句法规则的字符串。许多程序设计语言都支持利用正则表达式进行字符串操作。MongoDB 使用 $regex 操作符来设置匹配字符串的正则表达式。
语法一
{ <field>: { $regex: /pattern/, $options: '<options>' } }
{ <field>: { $regex: 'pattern', $options: '<options>' } }
{ <field>: { $regex: /pattern/<options> } }
语法二
{ <field>: /pattern/<options> }
2.案例演示
假设MongoDB中存放了我们OrderService服务的消息信息，其数据如下：
（以下为演示所用到的9个文档）
{ "_id" : ObjectId("5d305b1c4857fc49c0c14c81"), "order" : "QQ00001", "data" : ""<?xml version='1.0' encoding='UTF-8'?><Response service=\"OrderService\"><Head>ERR</Head><ERROR>重复下单</ERROR></Response>"" }, { "_id" : ObjectId("5d305b3b4857fc49c0c14c82"), "order" : "QQ00001", "data" : ""<?xml version='1.0' encoding='UTF-8'?><Response service=\"OrderService\"><Head>ERR</Head><ERROR>重复下单</ERROR></Response>"" }, { "_id" : ObjectId("5d305b404857fc49c0c14c83"), "order" : "QQ00002", "data" : ""<?xml version='1.0' encoding='UTF-8'?><Response service=\"OrderService\"><Head>ERR</Head><ERROR>重复下单</ERROR></Response>"" }, { "_id" : ObjectId("5d305b454857fc49c0c14c84"), "order" : "QQ00002", "data" : ""<?xml version='1.0' encoding='UTF-8'?><Response service=\"OrderService\"><Head>ERR</Head><ERROR>重复下单</ERROR></Response>"" }, { "_id" : ObjectId("5d305b4b4857fc49c0c14c85"), "order" : "QQ00003", "data" : ""<?xml version='1.0' encoding='UTF-8'?><Response service=\"OrderService\"><Head>ERR</Head><ERROR>重复下单</ERROR></Response>"" }, { "_id" : ObjectId("5d305b4f4857fc49c0c14c86"), "order" : "QQ00003", "data" : ""<?xml version='1.0' encoding='UTF-8'?><Response service=\"OrderService\"><Head>ERR</Head><ERROR>重复下单</ERROR></Response>"" }, { "_id" : ObjectId("5d305bb74857fc49c0c14c87"), "order" : "QQ00003", "data" : ""<?xml version='1.0' encoding='UTF-8'?><Response service=\"OrderService\"><Head>OK</Head><Body><OrderResponse filter_mmm=\"2\" destcity=\"shenzheng\" origincode=\"QQ0003\" /></Body></Response>"" }, { "_id" : ObjectId("5d305bd14857fc49c0c14c88"), "order" : "QQ00002", "data" : ""<?xml version='1.0' encoding='UTF-8'?><Response service=\"OrderService\"><Head>OK</Head><Body><OrderResponse filter_mmm=\"2\" destcity=\"zhongshan\" origincode=\"QQ0002\" /></Body></Response>"" }, { "_id" : ObjectId("5d305be94857fc49c0c14c89"), "order" : "QQ00001", "data" : ""<?xml version='1.0' encoding='UTF-8'?><Response service=\"OrderService\"><Head>OK</Head><Body><OrderResponse filter_mmm=\"2\" destcity=\"zhongshan\" origincode=\"QQ0001\" /></Body></Response>"" }
需求： 查询 data 字段 含有 字符 <Head>OK</Head>的文档
执行代码如下：
db.dbtestregex.find({data:{ $regex:/<Head>OK</Head>/}})
查询代码中的 为转移符，以下查询语句也是如此。
返回结果如下：
{ "_id" : ObjectId("5d305bb74857fc49c0c14c87"), "order" : "QQ00003", "data" : ""<?xml version='1.0' encoding='UTF-8'?><Response service=\"OrderService\"><Head>OK</Head><Body><OrderResponse filter_mmm=\"2\" destcity=\"shenzheng\" origincode=\"QQ0003\" /></Body></Response>"" }, { "_id" : ObjectId("5d305bd14857fc49c0c14c88"), "order" : "QQ00002", "data" : ""<?xml version='1.0' encoding='UTF-8'?><Response service=\"OrderService\"><Head>OK</Head><Body><OrderResponse filter_mmm=\"2\" destcity=\"zhongshan\" origincode=\"QQ0002\" /></Body></Response>"" }, { "_id" : ObjectId("5d305be94857fc49c0c14c89"), "order" : "QQ00001", "data" : ""<?xml version='1.0' encoding='UTF-8'?><Response service=\"OrderService\"><Head>OK</Head><Body><OrderResponse filter_mmm=\"2\" destcity=\"zhongshan\" origincode=\"QQ0001\" /></Body></Response>"" }
上面的查询命令也可以改写成：
db.dbtestregex.find({data:/<Head>OK</Head>/})
其查询结果是一样的，如下：
{ "_id" : ObjectId("5d305bb74857fc49c0c14c87"), "order" : "QQ00003", "data" : ""<?xml version='1.0' encoding='UTF-8'?><Response service=\"OrderService\"><Head>OK</Head><Body><OrderResponse filter_mmm=\"2\" destcity=\"shenzheng\" origincode=\"QQ0003\" /></Body></Response>"" }, { "_id" : ObjectId("5d305bd14857fc49c0c14c88"), "order" : "QQ00002", "data" : ""<?xml version='1.0' encoding='UTF-8'?><Response service=\"OrderService\"><Head>OK</Head><Body><OrderResponse filter_mmm=\"2\" destcity=\"zhongshan\" origincode=\"QQ0002\" /></Body></Response>"" }, { "_id" : ObjectId("5d305be94857fc49c0c14c89"), "order" : "QQ00001", "data" : ""<?xml version='1.0' encoding='UTF-8'?><Response service=\"OrderService\"><Head>OK</Head><Body><OrderResponse filter_mmm=\"2\" destcity=\"zhongshan\" origincode=\"QQ0001\" /></Body></Response>"" }
还可以写成：
db.dbtestregex.find({data:{ $regex:'<Head>OK</Head>'}})
其实现功能一样。
3.类关系型数据库中的 not like 功能实现
反向查询虽然不常见，但也是我们DBA必须的。下面我们做一个案例演示，看看在MongoDB中，怎么实现not like 功能的查询。
需求 查询data 字段中不含 <Head>OK</Head>的文档
执行脚本如下：
db.dbtestregex.find({data:{ $not: /<Head>OK</Head>/ }})
返回的文档如下;
{ "_id" : ObjectId("5d305b1c4857fc49c0c14c81"), "order" : "QQ00001", "data" : ""<?xml version='1.0' encoding='UTF-8'?><Response service=\"OrderService\"><Head>ERR</Head><ERROR>重复下单</ERROR></Response>"" }, { "_id" : ObjectId("5d305b3b4857fc49c0c14c82"), "order" : "QQ00001", "data" : ""<?xml version='1.0' encoding='UTF-8'?><Response service=\"OrderService\"><Head>ERR</Head><ERROR>重复下单</ERROR></Response>"" }, { "_id" : ObjectId("5d305b404857fc49c0c14c83"), "order" : "QQ00002", "data" : ""<?xml version='1.0' encoding='UTF-8'?><Response service=\"OrderService\"><Head>ERR</Head><ERROR>重复下单</ERROR></Response>"" }, { "_id" : ObjectId("5d305b454857fc49c0c14c84"), "order" : "QQ00002", "data" : ""<?xml version='1.0' encoding='UTF-8'?><Response service=\"OrderService\"><Head>ERR</Head><ERROR>重复下单</ERROR></Response>"" }, { "_id" : ObjectId("5d305b4b4857fc49c0c14c85"), "order" : "QQ00003", "data" : ""<?xml version='1.0' encoding='UTF-8'?><Response service=\"OrderService\"><Head>ERR</Head><ERROR>重复下单</ERROR></Response>"" }, { "_id" : ObjectId("5d305b4f4857fc49c0c14c86"), "order" : "QQ00003", "data" : ""<?xml version='1.0' encoding='UTF-8'?><Response service=\"OrderService\"><Head>ERR</Head><ERROR>重复下单</ERROR></Response>"" }
更多内容可参照官方文档 https://docs.mongodb.com/manual/reference/operator/query/regex/#op._S_regex