var persons = [{name:"jim",age:25,email:"75431457@qq.com",c:89,m:96,e:87,country:"USA",books:["JS","C++","EXTJS","MONGODB"]
},
{name:"tom",age:25,email:"214557457@qq.com",c:75,m:66,e:97,country:"USA",books:["PHP","JAVA","EXTJS","C++"]
},
{name:"lili",age:26,email:"344521457@qq.com",c:75,m:63,e:97,country:"USA",books:["JS","JAVA","C#","MONGODB"]
},
{name:"zhangsan",age:27,email:"2145567457@qq.com",c:89,m:86,e:67,country:"China",books:["JS","JAVA","EXTJS","MONGODB"]
},
{name:"lisi",age:26,email:"274521457@qq.com",c:53,m:96,e:83,country:"China",books:["JS","C#","PHP","MONGODB"]
},
{name:"wangwu",age:27,email:"65621457@qq.com",c:45,m:65,e:99,country:"China",books:["JS","JAVA","C++","MONGODB"]
},
{name:"zhaoliu",age:27,email:"214521457@qq.com",c:99,m:96,e:97,country:"China",books:["JS","JAVA","EXTJS","PHP"]
},
{name:"piaoyingjun",age:26,email:"piaoyingjun@uspcat.com",c:39,m:54,e:53,country:"Korea",books:["JS","C#","EXTJS","MONGODB"]
},
{name:"lizhenxian",age:27,email:"lizhenxian@uspcat.com",c:35,m:56,e:47,country:"Korea",books:["JS","JAVA","EXTJS","MONGODB"]
},
{name:"lixiaoli",age:21,email:"lixiaoli@uspcat.com",c:36,m:86,e:32,country:"Korea",books:["JS","JAVA","PHP","MONGODB"]
},
{name:"zhangsuying",age:22,email:"zhangsuying@uspcat.com",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:"jim"})
while(persons.hasNext()){obj = persons.next();print(obj.books.length)
} 

find：db.集合名.find({条件},{键指定})
1：只查找部分字段1.1 查询出所有数据的指定键(name ,age ,country)db.persons.find({},{name:1,age:1,country:1,_id:0});
2.查询条件$gte $gt $lte $lt  $ne2.1查询出年龄在25到27岁之间的学生db.persons.find({age: {$gte:25,$lte:27},{_id:0,age:1})2.2查询出所有不是韩国籍的学生的数学成绩db.persons.find({country:{$ne:” Korea”}},{_id:0,m:1})
3.包含或不包含$in或$nin2.3查询国籍是中国或美国的学生信息db.persons.find({country:{$in:[“USA”,“China”]}})2.4查询国籍不是中国或美国的学生信息db.persons.find({country:{$nin:[“USA”,“China”]}})
4.OR查询$or2.4查询语文成绩大于85或者英语大于90的学生信息db.persons.find({$or:[{c:{$gte:85}},{e:{$gte:90}}]},{_id:0,c:1,e:1})
5.Null把中国国籍的学生上增加新的键sexdb.person.update({country:”China”},{$set:{sex:”m”}})2.5查询出sex 等于 null的学生db.persons.find({sex:{$in:[null]}},{country:1})或者db.persons.find({sex:{$eq:null}})
6.正则查询2.6查询出名字中存在”li”的学生的信息db.persons.find({name:/li/i},{_id:0,name:1})
7.$not的使用$not可以用到任何地方进行取反操作2.7查询出名字中不存在”li”的学生的信息db.persons.find({name:{$not:/li/i}},{_id:0,name:1})$not和$nin的区别是$not可以用在任何地方儿$nin是用到集合上的
8.数组查询$all和index应用2.8查询喜欢看MONGOD和JS的学生db.persons.find({books:{$all:[“MONGOBD”,”JS”]}},{books:1,_id:0})2.8.2查询第二本书是JAVA的学习信息db.persons.find({“books.1”:”JAVA”})
9.查询指定长度数组$size它不能与比较查询符一起使用(这是弊端)2.9查询出喜欢的书籍数量小于4本的学生db.persons.find({$where:"this.books.length《4"})2.9.2查询出lili喜欢看的书的数量     var lili = db.persons.find({name:"lili"})while(lili.hasNext()){obj=lili.next()print(obj.books.length)}
10.$slice操作符返回文档中指定数组的内部值2.10查询出Jim书架中第2~4本书db.persons.find({name:"jim"},{books:{"$slice":[1,3]}})2.10.2查询出最后一本书db.persons.find({name:"jim"},{books:{"$slice":-1},_id:0,name:1})    

var jim = [{school :"K",score:"A"
},{school :"L",score:"B"
},{school :"J",score:"A+"
}]
db.persons.update({name:"jim"},{$set:{school:jim}})

3.文档查询3.1查询出在K上过学的学生db.persons.find({"school.school":"K"})3.2查询出在K上过学的学生，而且成绩中获得过A的学生db.persons.find({"school.school":"K","school.score":"A"})3.3查询出在K校成绩为A的学生db.persons.find({school:{$elemMatch:{"school":"K","score":"A"}}})
4.$where4.查询年龄大于22岁,喜欢看C#书,在K学校上过学的学生信息db.persons.find({age:22,books:{$in:["C#"]},"school.school":"K"})或者db.persons.find({"$where":function(){//得到查询结果的每一条文档var books = this.books;//得到文档中的school对象var school = this.school;//如果年纪>=22if(this.age > 22){var php = null;//遍历书籍for ( var i = 0; i < books.length; i++) {if(books[i] == "C++"){php = books[i];//如果学校是真if(school){for (var j = 0; j < school.length; j++) {//判断是不是在K上学if(school[j].school == "K"){//返回是真return true;}}break;}}}    }}})
5.Limit返回指定的数据条数5.1查询出persons文档中前5条数据db.persons.find({},{_id:0,name:1}).limit(5)
6.Skip返回指定数据的跨度6.1查询出persons文档中5~10条的数据db.persons.find({},{_id:0,name:1}).limit(5).skip(5)
7.Sort返回按照年龄排序的数据[1,-1]db.persons.find({},{_id:0,name:1,age:1}).sort({age:1})注意:mongodb的key可以存不同类型的数据排序就也有优先级最小值null数字字符串对象/文档数组二进制对象ID布尔日期时间戳  正则  最大值
8：分页（跳过多少条，去多少条）db.persons.find().limit(5).skip(5).sort({id:1})注意：分页的性能不好，建议通过，筛选条件+limit()，获取分页示例：根据自增的id取数据（每页5条，显示第二页）方法一：db.persons.find().limit(5).skip(5)方法二：db.persons.find({id:{$gt:5}}).limit(5) 而且，应该把重点放到便捷和精确查询上而不是分页的性能上
因为用户最多不会翻查过2页的