深入浅出MongoDB(四)：常用命令详细讲解
创建数据库，集合 由于MongoDB不是关系型数据库文件，实际上，它并不存在传统关系型数据库中所谓”数据库”的概念，当你第一次新增数据时，MongoDB就会以collection集合的开式进行保存和新建，而不需要你提前去建立 列出所有/当前的数据库使用show dbs命令查看所有的数据库, 用db命令查询当前链接的数据库
有些同学可能感觉到很奇怪，为什么连接了test数据库，在显示所有数据库的时候竟没有test呢？这是因为连接test时，并没有向其中写数据，所以并没有真正的建立、只是在使用当前的数据库。 定义新的数据库连接用“use 数据库名”来定义新的数据库连接，和上面的test一样，只是建立了连接
增加文档MongoDB插入原理：使用驱动程序进行插入的时候，会装数据转换成BSON格式，数据库会解析BSON，并检查是否含有“_id”键，因为“_id”键在插入到数据库时MongoDB会自动生成。 定义一个collection(集合)，名为users，然后插入文档：
首先用insert（用save也可以）语句插入一条数据，使用的是users集合，插入成功后查看所有的库，多了一个mydb库，再查看所有的集合(用show collections或show tables)，多了一个users集合，再用db.users.find()查看users集合中的所有文档。 可以增加字段
让id自增长的解决方案：定义一个函数，在插入_id时调用自己定义的函数来实现id自增
注：system.indexes是由所有文档的_id组成的索引集合。 存储在MongoDB集合中的每个文档都有一个默认的主键_id，它必须是唯一的，这个主键名称是固定的，它可以是MongoDB支持的任何数据类型，默认是ObjectId. Insert和save的不同点：如果已存在_id，Insert会插入失败，而save会更新原有的数据 删除文档删除文档用remove命令 语法格式：db.collname.remove({条件})，不写条件删除所有记录
更新文档先来创建两条记录，然后进行更新操作
我们用上面这种方法来更新另外一条记录
发现了没，sex字段竟没有了，这时候set关键字就派上用场了
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查询文档
查询用find或findOne（查询一条）
语法格式：db.collname.find({条件}),不写条件查询所有的数据
> db.users.find() { "_id" : ObjectId("50325c3595e66fd3daf3beac"), "name" : "mynosql" } { "_id" : ObjectId("50325c0a95e66fd3daf3beab"), "name" : "mongodbname" } { "_id" : ObjectId("50325e87b8e32f5aeae17d8c"), "name" : "nosqls", "sex" : "man" } > db.users.find ({name:"nosqls"}) { "_id" : ObjectId("50325e87b8e32f5aeae17d8c"), "name" : "nosqls", "sex" : "man" } > db.users.findOne() { "_id" : ObjectId("50325c3595e66fd3daf3beac"), "name" : "mynosql" } > |
查询指定的字段，_id默认是显示的，如果不要其显示，用_id:0
> db.users.find({name:'nosqls'}) { "_id" : ObjectId("50325e87b8e32f5aeae17d8c"), "name" : "nosqls", "sex" : "man" } > db.users.find({name:"nosqls"},{name:1}) { "_id" : ObjectId("50325e87b8e32f5aeae17d8c"), "name" : "nosqls" } > db.users.find({name:"nosqls"},{name:1,sex:1}) { "_id" : ObjectId("50325e87b8e32f5aeae17d8c"), "name" : "nosqls", "sex" : "man" } > db.users.find({name:"nosqls"},{name:1,sex:1,_id:0}) { "name" : "nosqls", "sex" : "man" } |
在mysql中，我们有这样的语句：
Select * from t1 order by age desc limit 1,2
Select count(*) from t1
这在MongoDB中是否也有类似的函数呢？答案是肯定的，下面我们来插入一些数据来操作
> for(i=1;i<=10;i++){ ... db.c1.insert({name:"user"+i,age:i}); ... } > db.c1.find() { "_id" : ObjectId("5032d0b73142123b5a215d50"), "name" : "user1", "age" : 1 } { "_id" : ObjectId("5032d0b73142123b5a215d51"), "name" : "user2", "age" : 2 } { "_id" : ObjectId("5032d0b73142123b5a215d52"), "name" : "user3", "age" : 3 } { "_id" : ObjectId("5032d0b73142123b5a215d53"), "name" : "user4", "age" : 4 } { "_id" : ObjectId("5032d0b73142123b5a215d54"), "name" : "user5", "age" : 5 } { "_id" : ObjectId("5032d0b73142123b5a215d55"), "name" : "user6", "age" : 6 } { "_id" : ObjectId("5032d0b73142123b5a215d56"), "name" : "user7", "age" : 7 } { "_id" : ObjectId("5032d0b73142123b5a215d57"), "name" : "user8", "age" : 8 } { "_id" : ObjectId("5032d0b73142123b5a215d58"), "name" : "user9", "age" : 9 } { "_id" : ObjectId("5032d0b73142123b5a215d59"), "name" : "user10", "age" : 10 } > |
用count()统计文档数
用sort来对文档进行排序，age:-1表示以age降序来显示，age:1表示以age升序来显示
用limit来限制输出几条文档，用skip跳过几个再输出，limit、skip、sort和count的可以组合使用
> db.c1.count() 10 > db.c1.find().sort({age:-1}) { "_id" : ObjectId("5032d0b73142123b5a215d59"), "name" : "user10", "age" : 10 } { "_id" : ObjectId("5032d0b73142123b5a215d58"), "name" : "user9", "age" : 9 } { "_id" : ObjectId("5032d0b73142123b5a215d57"), "name" : "user8", "age" : 8 } { "_id" : ObjectId("5032d0b73142123b5a215d56"), "name" : "user7", "age" : 7 } { "_id" : ObjectId("5032d0b73142123b5a215d55"), "name" : "user6", "age" : 6 } { "_id" : ObjectId("5032d0b73142123b5a215d54"), "name" : "user5", "age" : 5 } { "_id" : ObjectId("5032d0b73142123b5a215d53"), "name" : "user4", "age" : 4 } { "_id" : ObjectId("5032d0b73142123b5a215d52"), "name" : "user3", "age" : 3 } { "_id" : ObjectId("5032d0b73142123b5a215d51"), "name" : "user2", "age" : 2 } { "_id" : ObjectId("5032d0b73142123b5a215d50"), "name" : "user1", "age" : 1 } > db.c1.find().sort({age:1}) { "_id" : ObjectId("5032d0b73142123b5a215d50"), "name" : "user1", "age" : 1 } { "_id" : ObjectId("5032d0b73142123b5a215d51"), "name" : "user2", "age" : 2 } { "_id" : ObjectId("5032d0b73142123b5a215d52"), "name" : "user3", "age" : 3 } { "_id" : ObjectId("5032d0b73142123b5a215d53"), "name" : "user4", "age" : 4 } { "_id" : ObjectId("5032d0b73142123b5a215d54"), "name" : "user5", "age" : 5 } { "_id" : ObjectId("5032d0b73142123b5a215d55"), "name" : "user6", "age" : 6 } { "_id" : ObjectId("5032d0b73142123b5a215d56"), "name" : "user7", "age" : 7 } { "_id" : ObjectId("5032d0b73142123b5a215d57"), "name" : "user8", "age" : 8 } { "_id" : ObjectId("5032d0b73142123b5a215d58"), "name" : "user9", "age" : 9 } { "_id" : ObjectId("5032d0b73142123b5a215d59"), "name" : "user10", "age" : 10 } > db.c1.find().limit(2); { "_id" : ObjectId("5032d0b73142123b5a215d50"), "name" : "user1", "age" : 1 } { "_id" : ObjectId("5032d0b73142123b5a215d51"), "name" : "user2", "age" : 2 } > db.c1.find().sort({name:-1}).limit(2); { "_id" : ObjectId("5032d0b73142123b5a215d58"), "name" : "user9", "age" : 9 } { "_id" : ObjectId("5032d0b73142123b5a215d57"), "name" : "user8", "age" : 8 } > db.c1.find().skip(5).limit(3); { "_id" : ObjectId("5032d0b73142123b5a215d55"), "name" : "user6", "age" : 6 } { "_id" : ObjectId("5032d0b73142123b5a215d56"), "name" : "user7", "age" : 7 } { "_id" : ObjectId("5032d0b73142123b5a215d57"), "name" : "user8", "age" : 8 } > db.c1.find().skip(5).limit(3).count(); 10 > db.c1.find().skip(5).limit(3).count(1) 3 > db.c1.find().skip(5).limit(3).count(0) 10 |
注：
如果limit、skip、sort和count组合使用，是先排序、再跳过几条，然后再限制输出几条。
count如果不输入参数或者输入为0，会把find()后面的参数忽略，如果他的参数不为0，则统计在前面的条件过滤后的结果
条件表达式
1. <($lt),<=($lte),>($gt),>=($gte) ,!=($ne)
> db.c1.find({age:{$gt:5}}) { "_id" : ObjectId("5032d0b73142123b5a215d55"), "name" : "user6", "age" : 6 } { "_id" : ObjectId("5032d0b73142123b5a215d56"), "name" : "user7", "age" : 7 } { "_id" : ObjectId("5032d0b73142123b5a215d57"), "name" : "user8", "age" : 8 } { "_id" : ObjectId("5032d0b73142123b5a215d58"), "name" : "user9", "age" : 9 } { "_id" : ObjectId("5032d0b73142123b5a215d59"), "name" : "user10", "age" : 10 } > db.c1.find({age:{$gt:5,$lte:8}}) { "_id" : ObjectId("5032d0b73142123b5a215d55"), "name" : "user6", "age" : 6 } { "_id" : ObjectId("5032d0b73142123b5a215d56"), "name" : "user7", "age" : 7 } { "_id" : ObjectId("5032d0b73142123b5a215d57"), "name" : "user8", "age" : 8 } > |
2. $all
$all操作要求数组里面的值全部被包含在返回的记录里面，如：
> db.c2.insert({a:[123,1,2,3,4]}) > db.c2.find() { "_id" : ObjectId("5032d6a63142123b5a215d5a"), "a" : [ 123, 1, 2, 3, 4 ] } > db.c2.find({a:{$all:[2,3]}}) { "_id" : ObjectId("5032d6a63142123b5a215d5a"), "a" : [ 123, 1, 2, 3, 4 ] } > db.c2.find({a:{$all:[2,6]}}) > |
3. $exists
$exists操作检查一个字段是否存在，如：
> db.c2.find({age:{$exists:1}}) > db.c2.find({a:{$exists:1}}) { "_id" : ObjectId("5032d6a63142123b5a215d5a"), "a" : [ 123, 1, 2, 3, 4 ] } > |
4. $mod
$mod操作可以让我们简单的进行取模操作，而不需要用到where子句，如：
> db.c1.find({age:{$mod:[2,1]}}) { "_id" : ObjectId("5032d0b73142123b5a215d50"), "name" : "user1", "age" : 1 } { "_id" : ObjectId("5032d0b73142123b5a215d52"), "name" : "user3", "age" : 3 } { "_id" : ObjectId("5032d0b73142123b5a215d54"), "name" : "user5", "age" : 5 } { "_id" : ObjectId("5032d0b73142123b5a215d56"), "name" : "user7", "age" : 7 } { "_id" : ObjectId("5032d0b73142123b5a215d58"), "name" : "user9", "age" : 9 } > |
5. $in, $nin
$in操作类似于传统关系数据库中的IN, $nin跟$in操作相反
> db.c1.find({age:{$in:[4,5,6]}}) { "_id" : ObjectId("5032d0b73142123b5a215d53"), "name" : "user4", "age" : 4 } { "_id" : ObjectId("5032d0b73142123b5a215d54"), "name" : "user5", "age" : 5 } { "_id" : ObjectId("5032d0b73142123b5a215d55"), "name" : "user6", "age" : 6 } > db.c1.find({age:{$nin:[4,5,6]}}) { "_id" : ObjectId("5032d0b73142123b5a215d50"), "name" : "user1", "age" : 1 } { "_id" : ObjectId("5032d0b73142123b5a215d51"), "name" : "user2", "age" : 2 } { "_id" : ObjectId("5032d0b73142123b5a215d52"), "name" : "user3", "age" : 3 } { "_id" : ObjectId("5032d0b73142123b5a215d56"), "name" : "user7", "age" : 7 } { "_id" : ObjectId("5032d0b73142123b5a215d57"), "name" : "user8", "age" : 8 } { "_id" : ObjectId("5032d0b73142123b5a215d58"), "name" : "user9", "age" : 9 } { "_id" : ObjectId("5032d0b73142123b5a215d59"), "name" : "user10", "age" : 10 } > |
6. $nor跟$or
> db.c1.find({$or:[{name:"user2"},{name:"user3"}]}) { "_id" : ObjectId("5032d0b73142123b5a215d51"), "name" : "user2", "age" : 2 } { "_id" : ObjectId("5032d0b73142123b5a215d52"), "name" : "user3", "age" : 3 } > db.c1.find({$nor:[{name:"user2"},{name:"user3"},{name:"user4"},{name:"user5"}]}) { "_id" : ObjectId("5032d0b73142123b5a215d50"), "name" : "user1", "age" : 1 } { "_id" : ObjectId("5032d0b73142123b5a215d55"), "name" : "user6", "age" : 6 } { "_id" : ObjectId("5032d0b73142123b5a215d56"), "name" : "user7", "age" : 7 } { "_id" : ObjectId("5032d0b73142123b5a215d57"), "name" : "user8", "age" : 8 } { "_id" : ObjectId("5032d0b73142123b5a215d58"), "name" : "user9", "age" : 9 } { "_id" : ObjectId("5032d0b73142123b5a215d59"), "name" : "user10", "age" : 10 } > db.c1.find({$or:[{name:"user2"},{age:8}]}) { "_id" : ObjectId("5032d0b73142123b5a215d51"), "name" : "user2", "age" : 2 } { "_id" : ObjectId("5032d0b73142123b5a215d57"), "name" : "user8", "age" : 8 } > |
7. $size
$size操作将会查询数组长度等于输入参数的数组，例子：
> db.c2.find(); { "_id" : ObjectId("5032d6a63142123b5a215d5a"), "a" : [ 123, 1, 2, 3, 4 ] } { "_id" : ObjectId("50337a8aed4213674aebade4"), "b" : [ 568, 89, 52 ] } > db.c2.find({a:{$size:4}}) > db.c2.find({a:{$size:5}}) { "_id" : ObjectId("5032d6a63142123b5a215d5a"), "a" : [ 123, 1, 2, 3, 4 ] } |
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