分页与排序
1. limit() 返回指定条数的数据
a.查询出persons文档中前5条数据
> db.persons.find({},{_id:0}).limit(5)
{ "name" : "tom", "age" : 25, "email" : "214557457@qq.com", "c" : 75, "m" : 66, "e" : 97, "country" : "USA", "books" : [ "PHP", "JAVA", "EXTJS", "C++" ], "size" : 4 }
{ "name" : "lili", "age" : 26, "email" : "344521457@qq.com", "c" : 75, "m" : 63, "e" : 97, "country" : "USA", "books" : [ "JS", "JAVA", "C#", "MONGODB" ], "size" : 4 }
{ "name" : "zhangsan", "age" : 27, "email" : "2145567457@qq.com", "c" : 89, "m" : 86, "e" : 67, "country" : "China", "books" : [ "JS", "JAVA", "EXTJS", "MONGODB" ], "sex" : "M", "size" : 4 }
{ "name" : "lisi", "age" : 26, "email" : "274521457@qq.com", "c" : 53, "m" : 96, "e" : 83, "country" : "China", "books" : [ "JS", "C#", "PHP", "MONGODB" ], "sex" : "M", "size" : 4 }
{ "name" : "wangwu", "age" : 27, "email" : "65621457@qq.com", "c" : 45, "m" : 65, "e" : 99, "country" : "China", "books" : [ "JS", "JAVA", "C++", "MONGODB" ], "sex" : "M", "size" : 4 }
2.skip()返回指定数据的跨度
a.查询出persons文档中5~10条的数据
> db.persons.find({},{_id:0,name:1}).limit(5).skip(5)
{ "name" : "zhaoliu" }
{ "name" : "piaoyingjun" }
{ "name" : "lizhenxian" }
{ "name" : "lixiaoli" }
{ "name" : "zhangsuying" }
3.sort返回按照年龄排序的数据[1,-1]
1 : 顺序
-1:倒序
> db.persons.find({},{_id:0,name:1,age:1}).sort({age:1})
{ "name" : "lixiaoli", "age" : 21 }
{ "name" : "zhangsuying", "age" : 22 }
{ "name" : "tom", "age" : 25 }
{ "name" : "jim", "age" : 25 }
{ "name" : "lili", "age" : 26 }
{ "name" : "lisi", "age" : 26 }
{ "name" : "piaoyingjun", "age" : 26 }
{ "name" : "zhangsan", "age" : 27 }
{ "name" : "wangwu", "age" : 27 }
{ "name" : "zhaoliu", "age" : 27 }
{ "name" : "lizhenxian", "age" : 27 }
注意:mongodb的key可以存储不同类型的数据,排序也就有了优先级:
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
4.limit()和skip()完成分页
a.三条数据为一页进行分页
第一页:
> db.persons.find({},{_id:0,name:1}).limit(3).skip(0)
{ "name" : "tom" }
{ "name" : "lili" }
{ "name" : "zhangsan" }
第二页:
> db.persons.find({},{_id:0,name:1}).limit(3).skip(3)
{ "name" : "lisi" }
{ "name" : "wangwu" }
{ "name" : "zhaoliu" }
b.skip有性能问题,没有特殊情况下我们也可以换个思路
对文档进行重新结构设计:
增加Date键
在每次查询时候,前后台传值要把上次最后一个文档的日期保存下来
然后这样就可以做分页查询了:
db.person.find({date:{$gt:日期数值}}).limit(3)
个人建议: 应该把软件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页超过2页