MongoDB的查询

一、Find操作

二、分页和排序

三、游标的使用

一、Find查询

事前准备：插入如下数据

db.Students.insert([
{ _id:1,  name:"Zhao", age:25, country:"USA", books:["JS","C++","EXTJS","MONGODB"]},
{ _id:2, name:"Qian",age:22, country:"USA", books:["PHP","JAVA","EXTJS","C++"]},
{ _id:3,name:"Sun",age:26, country:"USA", books:["JS","JAVA","C#","MONGODB"]},
{ _id:4, name:"Li",age:27,country:"China",books:["JS","JAVA","EXTJS","MONGODB"]},
{ _id:5,name:"Zhou", age:30,country:"China",books:["JS","C#","PHP","MONGODB"]},
{ _id:6, name:"Wu", age:27, country:"Japan", books:["JS","JAVA","C++","MONGODB"]},
{ _id:7, name:"Zheng", age:27, country:"UK", books:["JS","JAVA","EXTJS","PHP"]},
{ _id:8, name:"Wang", age:26,  country:"Korea",books:["JS","C#","EXTJS","MONGODB"]}
]) 

1.指定返回的键

  db.[文档名].find ({条件},{键指定})

1.1 查询出所有数据的指定键(name ,age ,country)

db.Students.find({},{name:1,age:1,country:1,_id:0})

※条件不写就是查询全部

※需要查询的就在键后指定为1，不用就指定为0（感觉只要想查的键后面有值不见得非得是1）

※如果不指定显示=式_id:0,那查询过程都是带有_id的

例：查询所有学生的姓名和国家
> db.Students.find({},{name:1,country:1})
{ "_id" : 1, "name" : "Zhao", "country" : "USA" }
{ "_id" : 2, "name" : "Qian", "country" : "USA" }
{ "_id" : 3, "name" : "Sun", "country" : "USA" }
{ "_id" : 4, "name" : "Li", "country" : "China" }
{ "_id" : 5, "name" : "Zhou", "country" : "China" }
{ "_id" : 6, "name" : "Wu", "country" : "Japan" }
{ "_id" : 7, "name" : "Zheng", "country" : "UK" }
{ "_id" : 8, "name" : "Wang", "country" : "Korea" }
>

2.查询条件

比较操作符	意义	举例
$lt	<	查询出id小于5的学生 > db.Students.find({_id:{$lt:5}},{})
$lte	<=	查询出年龄小于等于25岁之间的学生 > db.Students.find({age:{$lte:25}},{})
$ne	!=	查询出国家不是中国的学生 > db.Students.find({country:{$ne:"China"}},{})
$gt	>	查询所有年纪大于27岁的，中国学生名字 > db.Students.find({age:{$gt:27}},{name:1,country:1,age:1}) { "_id" : 5, "name" : "Zhou", "age" : 30, "country" : "China" }
$gte	>=	同上

3.包含或不包含

较操作符	意义	举例
$in	包含	查询国家是中国和美国的学生 > db.Students.find({country:{$in:["China","USA"]}},{})
$nin	不包含	查询年龄不是27岁的学生 > db.Students.find({age:{$nin:[27]}},{})

4.OR查询

较操作符	意义	举例
$or	包含	查询年龄小于27岁，或者国家是美国的学生 >db.Students.find({$or:[{age:{$lt:27}},{country:"USA"}]},{}) 查询年龄大于等于30岁，或者国家是不是美国的学生 >db.Students.find({$or:[{age:{$gte:30}},{country:{$nin:["China"]}}]},{})

5.Null

为所有美国学生添加性别属性为男性（M）

> db.Students.update({country:"USA"},{$set:{sex:"M"}},false,true)

查询所有sex属性为null的学生

> db.Students.find({sex:{$in:[null]}},{name:1,country:1})

6.正则查询

查询出名字中存在”Zh”的学生的信息

> db.Students.find({name:/Zh/},{})
{ "_id" : 1, "name" : "Zhao", "age" : 25, "country" : "USA", "books" : [ "JS", "C++", "EXTJS", "MONGODB" ], "sex" : "M" }
{ "_id" : 5, "name" : "Zhou", "age" : 30, "country" : "China", "books" : [ "JS", "C#", "PHP", "MONGODB" ] }
{ "_id" : 7, "name" : "Zheng", "age" : 27, "country" : "UK", "books" : [ "JS", "JAVA", "EXTJS", "PHP" ] }

7.$not的使用

※$not和$nin的区别是$not可以用在任何地方儿$nin是用到集合上的

查找出名字中不存在“Zh”的学生信息

> db.Students.find({name:{$not:/Zh/}},{})
{ "_id" : 2, "name" : "Qian", "age" : 22, "country" : "USA", "books" : [ "PHP","JAVA", "EXTJS", "C++" ], "sex" : "M" }
{ "_id" : 3, "name" : "Sun", "age" : 26, "country" : "USA", "books" : [ "JS", "JAVA", "C#", "MONGODB" ], "sex" : "M" }
{ "_id" : 4, "name" : "Li", "age" : 27, "country" : "China", "books" : [ "JS", "JAVA", "EXTJS", "MONGODB" ] }
{ "_id" : 6, "name" : "Wu", "age" : 27, "country" : "Japan", "books" : [ "JS", "JAVA", "C++", "MONGODB" ] }
{ "_id" : 8, "name" : "Wang", "age" : 26, "country" : "Korea", "books" : [ "JS","C#", "EXTJS", "MONGODB" ] }

8.数组查询$all和index应用

查询所有拥有JS和PHP书籍的同学

> db.Students.find({books:{$all:["JS","PHP"]}},{})
{ "_id" : 5, "name" : "Zhou", "age" : 30, "country" : "China", "books" : [ "JS", "C#", "PHP", "MONGODB" ] }
{ "_id" : 7, "name" : "Zheng", "age" : 27, "country" : "UK", "books" : [ "JS", "JAVA", "EXTJS", "PHP" ] }

查询第三本书是C#的同学

> db.Students.find({"books.2":"C#"},{})
{ "_id" : 3, "name" : "Sun", "age" : 26, "country" : "USA", "books" : [ "JS", "JAVA", "C#", "MONGODB" ], "sex" : "M" }　

上面那个使用index来查询的例子中，"books.2"一定要用""包含起来

9.查询指定长度数组$size

它不能与比较查询符一起使用(这是弊端)

插入一条book数组有两本数的同学

> db.Students.insert({_id:9,name:"Xu",age:26,country:"Japan",books:["C#","PHP"]})
WriteResult({ "nInserted" : 1 })

查询只有两本书的同学

> db.Students.find({books:{$size:2}},{})
{ "_id" : 9, "name" : "Xu", "age" : 26, "country" : "Japan", "books" : [ "C#", "PHP" ] }

查询名字是“Li”的喜欢的书的数量

> var person = db.Students.find({name:"Li"})
> while(person.hasNext()){ obj = person.next(); print(obj.books.length) }

10.$slice操作符返回文档中指定数组的内部值

查询名字为“Wang”书架中第1~3本书

> db.Students.find({name:"Wang"},{books:{$slice:[0,3]}})
{ "_id" : 8, "name" : "Wang", "age" : 26, "country" : "Korea", "books" : [ "JS", "C#", "EXTJS" ] }

查询出最后一本书

> db.Students.find({name:"Wang"},{books:{$slice:-1}})
{ "_id" : 8, "name" : "Wang", "age" : 26, "country" : "Korea", "books" : [ "MONGODB" ] }　　

11.文档查询

添加一个对象数组到“Li”同学，记录“Li”同学的成绩

> var li = [{

... subject :"Math",

... score: 90

... },{

... subject :"English",

... score:85

... },{

... subject :"History",

... score:95

... }]

> db.Students.update({name:"Li"},{$set:{school:li}})

WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })

> db.Students.find({name:"Li"},{})

{ "_id" : 4, "name" : "Li", "age" : 27, "country" : "China", "books" : [ "JS", "JAVA", "EXTJS", "MONGODB" ],

 "school" : [{ "subject" : "Math", "score" : 90 },{ "subject" : "English", "score" : 85 }, { "subject" : "History", "score" : 95 }]
}

>

查询参加了数学考试，并且分数为90的同学

①.绝对匹配可以

> db.Students.find({school:{subject:"Math",score:90}},{_id:0,name:1})
{ "name" : "Li" }　　

但是问题存在如下：

条件顺序变化时候，

> db.Students.find({school:{score:90,subject:"Math"}},{_id:0,name:1})
> --查不到东西--　

条件数目不一致的时候，也同样查不到

②.为了解决顺序的问题我可以用对象“.”

> db.Students.find({"school.subject":"Math","school.score":90},{name:1})
{ "_id" : 4, "name" : "Li" }

这种方式支持顺序的变化，但是也同样存在问题，那就是匹配的问题，条件不是作为一对条件来进行匹配的

例如：

> db.Students.find({"school.subject":"Math","school.score":85},{name:1})
{ "_id" : 4, "name" : "Li" }　

这里的85分是英语成绩

③.正确做法单条条件组查询$elemMatch

> db.Students.find({school:{$elemMatch:{subject:"Math",score:90}}},{name:1})
{ "_id" : 4, "name" : "Li" }
> db.Students.find({school:{$elemMatch:{score:90,subject:"Math"}}},{name:1})
{ "_id" : 4, "name" : "Li" }
> db.Students.find({school:{$elemMatch:{subject:"Math"}}},{name:1})
{ "_id" : 4, "name" : "Li" }
>

二、分页与排序

1.Limit返回指定的数据条数

查询出Student文档中前5条数据

> db.Students.find().limit(5)

2.Skip返回指定数据的跨度

查询出persons文档中3~8条的数据

> db.Students.find().limit(5).skip(2)

3.Sort返回按照年龄排序的数据[1,-1]

查询所有数据，按照年龄排序

正序
> db.Students.find({},{_id:0,age:1,name:1}).sort({age:1})
{ "name" : "Qian", "age" : 22 }
{ "name" : "Zhao", "age" : 25 }
{ "name" : "Sun", "age" : 26 }
{ "name" : "Wang", "age" : 26 }
{ "name" : "Xu", "age" : 26 }
{ "name" : "Wu", "age" : 27 }
{ "name" : "Zheng", "age" : 27 }
{ "name" : "Li", "age" : 27 }
{ "name" : "Zhou", "age" : 30 }
倒序
> db.Students.find({},{_id:0,age:1,name:1}).sort({age:-1})
{ "name" : "Zhou", "age" : 30 }
{ "name" : "Wu", "age" : 27 }
{ "name" : "Zheng", "age" : 27 }
{ "name" : "Li", "age" : 27 }
{ "name" : "Sun", "age" : 26 }
{ "name" : "Wang", "age" : 26 }
{ "name" : "Xu", "age" : 26 }
{ "name" : "Zhao", "age" : 25 }
{ "name" : "Qian", "age" : 22 }
>

skip性能不好，可以采用插入时间的做法来弥补，具体方法如下：

1.在每一个记录后面都加入一个插入时间的键值对

2.每次取数据的时候都把取出的最后一个数据的时间保存下来，再传给下一次查询

3.使用 db.persons.find({date:{$gt:日期数值}}).limit(取出的数据数目)比较查询取出要分页的数据

　　

三、游标和其他知识

1.利用游标来查询数据

    var  persons = db.persons.find();
    while(persons.hasNext()){
    obj = persons.next();
          print(obj.name)
     }

2.游标几个销毁条件　　

客户端发来信息叫他销毁

游标迭代完毕

默认游标超过10分钟没用也会别清除

3.查询快照

快照后就会针对不变的集合进行游标运动了,看看使用方法.

db.persons.find({$query:{name:”Jim”},$snapshot:true})

为什么用快照，以为MongoDB在进行更新的时候，例如添加一些键值对，那么MongoDB的处理不会在原来的索引位置上进行更新操作，而是会把

更新之后的数据，放在末尾，那么就导致了前后两次进行查询时候相同索引对应不同数据的情况

补充：

高级查询选项

$where

$query

$orderby

$maxsan：integer 最多扫描的文档数

$min：doc  查询开始

$max：doc  查询结束

$hint：doc   使用哪个索引

$explain:boolean  统计

$snapshot:boolean 一致快照