一、Find查询
事前准备：插入如下数据
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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})
查询出所有数据的指定键(name ,age ,country)
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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
2.查询条件
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比较操作符 |
意义 |
举例 |
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$lt |
< |
查询出id小于5的学生 > db.Students.find({_id:{$lt:5}},{}) |
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$lte |
<= |
查询出年龄小于等于25岁之间的学生 > db.Students.find({age:{$lte:25}},{}) |
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$ne |
!= |
查询出国家不是中国的学生 > db.Students.find({country:{$ne:"China"}},{}) |
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$gt |
> |
查询所有年纪大于27岁的，中国学生名字 > db.Students.find({age:{$gt:27}},{name:1,country:1,age:1}) { "_id" : 5, "name" : "Zhou", "age" : 30, "country" : "China" } |
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$gte |
>= |
同上 |
3.包含或不包含
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较操作符 |
意义 |
举例 |
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$in |
包含 |
查询国家是中国和美国的学生 > db.Students.find({country:{$in:["China","USA"]}},{}) |
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$nin |
不包含 |
查询年龄不是27岁的学生 > db.Students.find({age:{$nin:[27]}},{}) |
4.OR查询
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较操作符 |
意义 |
举例 |
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$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:{$nin:["China"]}}]},{}) |
5.Null
为所有美国学生添加性别属性为男性（M）
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> db.Students.update({country:"USA"},{$set:{sex:"M"}},false,true) |
查询所有sex属性为null的学生
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> db.Students.find({sex:{$in:[null]}},{name:1,country:1}) |
6.正则查询
查询出名字中存在”Zh”的学生的信息
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> db.Students.find({name:/Zh/},{}){ "_id" : 1, "name" : "Zhao", "age" : 25, "country" : "USA", "books" : [ "JS", "C++", "EXTJS", "MONGODB" ], "sex" : "M" }{ "_id" : 5, "name" : "Zhou", "age" : 30, "country" : "China", "books" : [ "JS", "C#", "PHP", "MONGODB" ] }{ "_id" : 7, "name" : "Zheng", "age" : 27, "country" : "UK", "books" : [ "JS", "JAVA", "EXTJS", "PHP" ] } |
7.$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
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> 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
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> db.Students.find({books:{$all:["JS","PHP"]}},{}){ "_id" : 5, "name" : "Zhou", "age" : 30, "country" : "China", "books" : [ "JS", "C#", "PHP", "MONGODB" ] }{ "_id" : 7, "name" : "Zheng", "age" : 27, "country" : "UK", "books" : [ "JS", "JAVA", "EXTJS", "PHP" ] } |
查询第三本书是C#的同学
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> db.Students.find({"books.2":"C#"},{}){ "_id" : 3, "name" : "Sun", "age" : 26, "country" : "USA", "books" : [ "JS", "JAVA", "C#", "MONGODB" ], "sex" : "M" } |
上面那个使用index来查询的例子中，"books.2"一定要用""包含起来
9.查询指定长度数组$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
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> 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
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> db.Students.find({books:{$size:2}},{}){ "_id" : 9, "name" : "Xu", "age" : 26, "country" : "Japan", "books" : [ "C#", "PHP" ] } |
查询名字是“Li”的喜欢的书的数量
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> var person = db.Students.find({name:"Li"})> while(person.hasNext()){ obj = person.next(); print(obj.books.length) } |
10.$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
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> db.Students.find({name:"Wang"},{books:{$slice:[0,3]}}){ "_id" : 8, "name" : "Wang", "age" : 26, "country" : "Korea", "books" : [ "JS", "C#", "EXTJS" ] } |
查询出最后一本书
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> db.Students.find({name:"Wang"},{books:{$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
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> var li = [{ ... subject :"Math", ... score: 90 ... },{ ... subject :"English", ... score:85 ... },{ ... subject :"History", ... score:95 ... }] > db.Students.update({name:"Li"},{$set:{school:li}}) WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 }) > db.Students.find({name:"Li"},{}) { "_id" : 4, "name" : "Li", "age" : 27, "country" : "China", "books" : [ "JS", "JAVA", "EXTJS", "MONGODB" ], "school" : [{ "subject" : "Math", "score" : 90 },{ "subject" : "English", "score" : 85 }, { "subject" : "History", "score" : 95 }]} > |
查询参加了数学考试，并且分数为90的同学
①.绝对匹配可以
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> db.Students.find({school:{subject:"Math",score:90}},{_id:0,name:1}){ "name" : "Li" } |
但是问题存在如下：
条件顺序变化时候，
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> db.Students.find({school:{score:90,subject:"Math"}},{_id:0,name:1})> --查不到东西-- |
条件数目不一致的时候，也同样查不到
②.为了解决顺序的问题我可以用对象“.”
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> db.Students.find({"school.subject":"Math","school.score":90},{name:1}){ "_id" : 4, "name" : "Li" } |
这种方式支持顺序的变化，但是也同样存在问题，那就是匹配的问题，条件不是作为一对条件来进行匹配的
例如：
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> db.Students.find({"school.subject":"Math","school.score":85},{name:1}){ "_id" : 4, "name" : "Li" } |
这里的85分是英语成绩
③.正确做法单条条件组查询$elemMatch
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> 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:{$elemMatch:{subject:"Math"}}},{name:1}){ "_id" : 4, "name" : "Li" }> |
二、分页与排序
1.Limit返回指定的数据条数
查询出Student文档中前5条数据
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> db.Students.find().limit(5) |
2.Skip返回指定数据的跨度
查询出persons文档中3~8条的数据
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> db.Students.find().limit(5).skip(2) |
3.Sort返回按照年龄排序的数据[1,-1]
查询所有数据，按照年龄排序
正序
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> db.Students.find({},{_id:0,age:1,name:1}).sort({age:1}){ "name" : "Qian", "age" : 22 }{ "name" : "Zhao", "age" : 25 }{ "name" : "Sun", "age" : 26 }{ "name" : "Wang", "age" : 26 }{ "name" : "Xu", "age" : 26 }{ "name" : "Wu", "age" : 27 }{ "name" : "Zheng", "age" : 27 }{ "name" : "Li", "age" : 27 }{ "name" : "Zhou", "age" : 30 } |
倒序
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> db.Students.find({},{_id:0,age:1,name:1}).sort({age:-1}){ "name" : "Zhou", "age" : 30 }{ "name" : "Wu", "age" : 27 }{ "name" : "Zheng", "age" : 27 }{ "name" : "Li", "age" : 27 }{ "name" : "Sun", "age" : 26 }{ "name" : "Wang", "age" : 26 }{ "name" : "Xu", "age" : 26 }{ "name" : "Zhao", "age" : 25 }{ "name" : "Qian", "age" : 22 }> |
skip性能不好，可以采用插入时间的做法来弥补，具体方法如下：
- 1.在每一个记录后面都加入一个插入时间的键值对
- 2.每次取数据的时候都把取出的最后一个数据的时间保存下来，再传给下一次查询
- 3.使用db.persons.find({date:{$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
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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.
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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
到此这篇关于MongoDB实现查询操作的文章就介绍到这了。希望对大家的学习有所帮助，也希望大家多多支持服务器之家。
原文链接：https://www.cnblogs.com/dcz2015/p/5251309.html
