mongoDB 比较运算符

比较运算符是我们学习任何语言或系统中最为常见的运算符之一。mongoDB的比较运算符，跟Linux的差不多，只不过每一个比较运算符前面会带有符号，他们分别是$eq、$gt、$gte、$lt、$lte、$ne、$in、nin等，下面将对这几个运算符进行描述。

一、比较运算符

  $eq    =               "="
  $gt   (greater than )  >
  $gte                   >=  (equal)
  $lt   (less than)      <
  $lte                   <=  (equal)
  $ne   (not equal)      !=
  $in                    in
  $nin  (not in)         !in

    重点：所有的比较运算符都是出现在键与值得中间，示例如下
            { <field_name>: { $operator: <value> } }
            { <ename>: { $eq: "robin" } }
            { <qty>: { $gt: 20 } }

二、比较运算符示例

1. $eq

     { <field>: {\$eq: <value> } }
        $eq表达式与{ field: <value> }等价
        <1> 支持简单匹配
        <2> 支持文档匹配(document，逐字段比较)
        <3> 支持数组匹配(array，有顺序要求)

    //单值匹配
    db.persons.find( { age: { $eq: 25 } } )
    db.persons.find( { age: 25 } )        //与上一条语句等价         

    //多值匹配
    db.persons.find( { age: { $eq: 25 } ,country: "USA"} )
    db.persons.find({$and:[{age:{$eq:25}},{country:{$eq:"USA"}}]}) //也可以使用$and运算符

    //嵌套文档匹配
    db.persons.find( { score: {"c" : 75, "m" : 63,"e" : 97}} )

    db.persons.find({"score.c":{$eq:89}}) //可以使用基于.成员的方式进行匹配
    db.persons.find({"score.c":89})          //等价的查询方式

    //数组匹配
    db.persons.find({"books":{$eq:"PHP"}})  //forech查找，不包含A的数组不会被返回
    db.persons.find({"books":{$in:["PHP"]}})  //也可以使用$in方式替代
    db.persons.find({"books":"PHP"})        //等价方式

2. $gt/$gte

    {field: {$gt: value} }

    db.persons.find( { age: { $gt: 20 } } )                   //大于运算符
    db.persons.find( { age: { $gte: 25 } } ).sort({"age":-1}) //大于等于运算符及倒序排列

3. $lt/$lte

    Syntax: {field: {$lt: value} }

    db.persons.find( { age: { $lt: 25 } } )
    db.persons.find( { age: { $lte: 25 } } ).sort({"age":-1})
    db.persons.find( { age: { $lte: 25 } } )

4. $ne

    Syntax: {field: {$ne: value} }

    db.persons.find( { age: { $ne: 20 } } ).sort({"age":-1})

5. $in

    Syntax: { field: { $in: [<value1>, <value2>, ... <valueN> ] } }

    db.persons.find( { age: { $in: [ 25, 27 ] } } )  //多值匹配
    db.persons.find( { books: { $in: [ /^JA/, /^PH/ ] } } ) //正则表达式匹配，查询以JA以及PH开头的
    //Author : Leshami
    //Blog   : http://blog.csdn.net/leshami

6. $nin

    Syntax: { field: { $nin: [ <value1>, <value2> ... <valueN> ]} }

    db.persons.find( { age: { $nin: [ 25, 27 ] } } ).sort({"name":-1});
    db.persons.update({ books: { $nin:["JAVA","PHP"]} },{$set: { age:100 }}) //基于$nin的文档更新

三、演示用到的示例文档

var persons = [{
    name:"robinson.cheng",
    age:25,
    email:"robinson.cheng@qq.com",
    score:{c:89,m:96,e:87},
    country:"USA",
    books:["JS","C++","EXTJS","MONGODB"]
},
{
    name:"tom.tong",
    age:25,
    email:"tom.tong@qq.com",
    score:{c:75,m:66,e:97},
    country:"USA",
    books:["PHP","JAVA","EXTJS","C++"]
},
{
    name:"jerry.liu",
    age:26,
    email:"jerry.liu@qq.com",
    score:{c:75,m:63,e:97},
    country:"USA",
    books:["JS","JAVA","C#","MONGODB"]
},
{
    name:"henry.ye",
    age:27,
    email:"henry.ye@qq.com",
    score:{c:89,m:86,e:67},
    country:"China",
    books:["JS","JAVA","EXTJS","MONGODB"]
},
{
    name:"lisi",
    age:26,
    email:"lisi@qq.com",
    score:{c:53,m:96,e:83},
    country:"China",
    books:["JS","C#","PHP","MONGODB"]
},
{
    name:"fred.shu",
    age:27,
    email:"fred.shu@qq.com",
    score:{c:45,m:65,e:99},
    country:"China",
    books:["JS","JAVA","C++","MONGODB"]
},
{
    name:"jason.wu",
    age:27,
    email:"jason.wu@qq.com",
    score:{c:99,m:96,e:97},
    country:"China",
    books:["JS","JAVA","EXTJS","PHP"]
},
{
    name:"david.xiao",
    age:26,
    email:"david.xiao@dbsupport.cn",
    score:{c:39,m:54,e:53},
    country:"Korea",
    books:["JS","C#","EXTJS","MONGODB"]
},
{
    name:"frank.hu",
    age:27,
    email:"frank.hu@dbsupport.cn",
    score:{c:35,m:56,e:47},
    country:"Korea",
    books:["JS","JAVA","EXTJS","MONGODB"]
},
{
    name:"joe.zhou",
    age:21,
    email:"joe.zhou@dbsupport.cn",
    score:{c:36,m:86,e:32},
    country:"Korea",
    books:["JS","JAVA","PHP","MONGODB"]
},
{
    name:"steve.tang",
    age:22,
    email:"steve.tang@dbsupport.cn",
    score:{c:45,m:63,e:77},
    country:"Korea",
    books:["JS","JAVA","C#","MONGODB"]
}]
for(var i = 0;i<persons.length;i++){
    db.persons.insert(persons[i])
}
var persons = db.persons.find({name:"robinson.cheng"})
while(persons.hasNext()){
    obj = persons.next();
        print(obj.books.length)
}