MongoDB学习札记 第四篇 Query

MongoDB学习札记 第四篇 Query

查询条件

首先往数据库集合里面插入几条数据。
测试数据：

> db.users.insert({username:"mongo", url:"webinglin.github.io", tags:["mongodb", database","nosql"],likes:999, author:"linwenbin"})
> db.users.insert({username:"redis", url:"webinglin.github.io", tags:["redis","database","nosql"],likes:888, author:"linwenbin"})
> db.users.insert({username:"spring", url:"webinglin.github.io", tags:["spring","framework"],likes:777, author:"linwenbin"})



> db.users.find().pretty()
{
        "_id" : ObjectId("5574bdabc705777157a515aa"),
        "username" : "mongo",
        "url" : "webinglin.github.io",
        "tags" : [
                "mongodb",
                "database",
                "nosql"
        ],
        "likes" : 999,
        "author" : "linwenbin"
}
{
        "_id" : ObjectId("5574bdd2c705777157a515ab"),
        "username" : "redis",
        "url" : "webinglin.github.io",
        "tags" : [
                "redis",
                "database",
                "nosql"
        ],
        "likes" : 888,
        "author" : "linwenbin"
}
{
        "_id" : ObjectId("5574bdf3c705777157a515ac"),
        "username" : "spring",
        "url" : "webinglin.github.io",
        "tags" : [
                "spring",
                "framework"
        ],
        "likes" : 777,
        "author" : "linwenbin"
}

pretty() 方法是对查询结果进行格式化

查询的时候可以带上查询条件,那具体的查询条件怎么使用？

等于

等于操作直接使用 {key:value} 这样的文档形式即可

> db.users.find({username:"mongo"})
{ "_id" : ObjectId("5574bdabc705777157a515aa"), "username" : "mongo", "url" : "webinglin.github.io", "tags" : [ "mongodb", "database", "nosql" ], "likes" : 999, "author" : "linwenbin" }
>

大于

语法： {key : {$gt:value} }

> db.users.find({likes:{$gt:888}})
{ "_id" : ObjectId("5574bdabc705777157a515aa"), "username" : "mongo", "url" : "webinglin.github.io", "tags" : [ "mongodb", "database", "nosql" ], "likes" : 999, "author" : "linwenbin" }
>

大于等于

语法： {key : {$gte:value} }

> db.users.find({likes:{$gte:888}})
{ "_id" : ObjectId("5574bdabc705777157a515aa"), "username" : "mongo", "url" : "webinglin.github.io", "tags" : [ "mongodb", "database", "nosql" ], "likes" : 999, "author" : "linwenbin" }
{ "_id" : ObjectId("5574bdd2c705777157a515ab"), "username" : "redis", "url" : "webinglin.github.io", "tags" : [ "redis", "database", "nosql" ], "likes" : 888, "author" : "linwenbin" }

小于

语法：　{key : {$lt:value} }

> db.users.find({likes:{$lt:888}})
{ "_id" : ObjectId("5574bdf3c705777157a515ac"), "username" : "spring", "url" : "webinglin.github.io", "tags" : [ "spring", "framework" ], "likes" : 777, "author" : "linwenbin" }

小于等于

语法：　{key : {$lte:value}}

> db.users.find({likes:{$lte:888}})
{ "_id" : ObjectId("5574bdd2c705777157a515ab"), "username" : "redis", "url" : "webinglin.github.io", "tags" : [ "redis", "database", "nosql" ], "likes" : 888, "author" : "linwenbin" }
{ "_id" : ObjectId("5574bdf3c705777157a515ac"), "username" : "spring", "url" : "webinglin.github.io", "tags" : [ "spring", "framework" ], "likes" : 777, "author" : "linwenbin" }

不等于

语法： {key : {$ne:value} }

> db.users.find({likes:{$ne:888}})
{ "_id" : ObjectId("5574bdabc705777157a515aa"), "username" : "mongo", "url" : "webinglin.github.io", "tags" : [ "mongodb", "database", "nosql" ], "likes" : 999, "author" : "linwenbin" }
{ "_id" : ObjectId("5574bdf3c705777157a515ac"), "username" : "spring", "url" : "webinglin.github.io", "tags" : [ "spring", "framework" ], "likes" : 777, "author" : "linwenbin" }

且操作 AND

语法： {key1:value1, key2:value2, key3:value3 …}

> db.users.find({likes:{$gt:777},username:"mongo"})
{ "_id" : ObjectId("5574bdabc705777157a515aa"), "username" : "mongo", "url" : "webinglin.github.io", "tags" : [ "mongodb", "database", "nosql" ], "likes" : 999, "author" : "linwenbin" }

> db.users.find({likes:{$gt:777}})
{ "_id" : ObjectId("5574bdabc705777157a515aa"), "username" : "mongo", "url" : "webinglin.github.io", "tags" : [ "mongodb", "database", "nosql" ], "likes" : 999, "author" : "linwenbin" }
{ "_id" : ObjectId("5574bdd2c705777157a515ab"), "username" : "redis", "url" : "webinglin.github.io", "tags" : [ "redis", "database", "nosql" ], "likes" : 888, "author" : "linwenbin" }

或操作 OR

语法： { $or: [ {key1: value1}, {key2:value2} ] } 将or条件的所有 {key:value} 都放在 $or 的value中（数组）

> db.users.find({$or:[{username:"mongo"},{username:"redis"}]})
{ "_id" : ObjectId("5574bdabc705777157a515aa"), "username" : "mongo", "url" : "webinglin.github.io", "tags" : [ "mongodb", "database", "nosql" ], "likes" : 999, "author" : "linwenbin" }
{ "_id" : ObjectId("5574bdd2c705777157a515ab"), "username" : "redis", "url" : "webinglin.github.io", "tags" : [ "redis", "database", "nosql" ], "likes" : 888, "author" : "linwenbin" }

复杂条件查询

如何将所有的条件都连起来用呢？

比如我们想要这样查询 like>=888 && (username=”mongo” or username=”spring”)
由于上面的数据只有三条， 我们知道 like>=888 只有 mongo 和 redis 这两条数据满足条件， 后面的username=”mongo” or username=”spring” 又有 mongo和 spring 满足条件， 这两个and操作之后 就只剩下 mongo 这条数据满足条件了。 所以最终应该查出一条mongo的Document.

> db.users.find({likes:{$gte:888},$or:[{username:"mongo"},{username:"spring"}]})
{ "_id" : ObjectId("5574bdabc705777157a515aa"), "username" : "mongo", "url" : "webinglin.github.io", "tags" : [ "mongodb", "database", "nosql" ], "likes" : 999, "author" : "linwenbin" }
>

find() 其他用法

Projection

mongodb中 projection 意味着显示你希望看到的字段而非所有的字段都显示,这是什么意思呢？

比如： 我们的测试数据里面有那么多的字段: username,likes,tags,author,url 而我们经常要用到的就只有 username 和 likes 那么就显示这两个字段就好了，其他的字段就别显示出来了。

find({},{KEY:1/0}) find的第二个参数，KEY为要显示或隐藏的字段，value为1表示显示，0表示隐藏，看着也很简单，试一下吧

> db.users.find({},{_id:0,url:0,tags:0,author:0})
{ "username" : "mongo", "likes" : 999 }
{ "username" : "redis", "likes" : 888 }
{ "username" : "spring", "likes" : 777 }
>

limit, skip, sort

为了更好的测试分页的效果，新建一个集合，并插入30条数据

> for(var i=0; i<30; i++){
... db.pages.insert({"val":i});
... }
WriteResult({ "nInserted" : 1 })
> db.pages.find()
{ "_id" : ObjectId("5574ca7b192e9dda0925e37f"), "val" : 0 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e380"), "val" : 1 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e381"), "val" : 2 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e382"), "val" : 3 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e383"), "val" : 4 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e384"), "val" : 5 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e385"), "val" : 6 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e386"), "val" : 7 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e387"), "val" : 8 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e388"), "val" : 9 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e389"), "val" : 10 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e38a"), "val" : 11 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e38b"), "val" : 12 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e38c"), "val" : 13 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e38d"), "val" : 14 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e38e"), "val" : 15 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e38f"), "val" : 16 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e390"), "val" : 17 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e391"), "val" : 18 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e392"), "val" : 19 }
Type "it" for more



> db.pages.find().limit(5)
{ "_id" : ObjectId("5574ca7b192e9dda0925e37f"), "val" : 0 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e380"), "val" : 1 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e381"), "val" : 2 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e382"), "val" : 3 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e383"), "val" : 4 }

可以发现，如果使用 limit方法的话会显示整个集合的所有文档。 指定了 limit 之后， 显示具体的条数，上文中，limit(5) 表示， 显示5条文档。

limit方法除外，还有一个 skip 方法，skip也是接受一个整型的参数，表示查询结果跳过多少个文档。

例如上面插入的30条记录中，我们要显示18-22条记录，那么就应该使用
db.pages.find().skip(18).limit(5)

> db.pages.find().skip(18).limit(5)
{ "_id" : ObjectId("5574ca7b192e9dda0925e391"), "val" : 18 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e392"), "val" : 19 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e393"), "val" : 20 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e394"), "val" : 21 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e395"), "val" : 22 }

skip和limit的组合就能做到分页的功能了。但是如果数据量很大，理论上分页就会变得很慢了，比如有一亿条数据，要拿最后一页。那skip的数据量就很多很多了。这样就会变得比较慢。话说回来，有谁会看数据看到最后的几页？正常都是看前面几页数据，所以，skip和limit实现分页是可以接受的。

在mongodb中，如果要对查询结果排序，那么需要使用sort方法。sort方法接收一个文档参数。也就是{key:value}的形式。其中，key表示要排序的字段，value的可取值为 1 / -1 。1表示升序asc，-1表示降序desc。话不多说，直接上例子：

> db.pages.find().sort({val:-1})
{ "_id" : ObjectId("5574ca7b192e9dda0925e39c"), "val" : 29 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e39b"), "val" : 28 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e39a"), "val" : 27 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e399"), "val" : 26 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e398"), "val" : 25 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e397"), "val" : 24 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e396"), "val" : 23 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e395"), "val" : 22 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e394"), "val" : 21 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e393"), "val" : 20 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e392"), "val" : 19 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e391"), "val" : 18 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e390"), "val" : 17 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e38f"), "val" : 16 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e38e"), "val" : 15 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e38d"), "val" : 14 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e38c"), "val" : 13 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e38b"), "val" : 12 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e38a"), "val" : 11 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e389"), "val" : 10 }
Type "it" for more

这个是对val这个key进行逆序排序，所以value取值为-1。 那value值为1的话，就变成升序了。

> db.pages.find().sort({val:1})
{ "_id" : ObjectId("5574ca7b192e9dda0925e37f"), "val" : 0 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e380"), "val" : 1 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e381"), "val" : 2 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e382"), "val" : 3 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e383"), "val" : 4 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e384"), "val" : 5 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e385"), "val" : 6 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e386"), "val" : 7 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e387"), "val" : 8 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e388"), "val" : 9 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e389"), "val" : 10 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e38a"), "val" : 11 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e38b"), "val" : 12 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e38c"), "val" : 13 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e38d"), "val" : 14 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e38e"), "val" : 15 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e38f"), "val" : 16 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e390"), "val" : 17 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e391"), "val" : 18 }
{ "_id" : ObjectId("5574ca7b192e9dda0925e392"), "val" : 19 }
Type "it" for more
>

那如果要对多个值进行组合排序呢？ 就好比如对于我们最初的例子 users 集合。 要对users集合进行排序。其中 按照likes升序， 按照username降序。为了达到我们的效果，我们再往users集合里面插入两条数据

> db.users.insert({username:"mongodb",likes:999})
> db.users.insert({username:"springMVC",likes:888})

下面是运行结果，注意观察 likes为888的两个文档。发现username逆序排序了。至此，说明我们的sort实验成功了。

> db.users.find().sort({likes:1,username:-1}).pretty()
{
        "_id" : ObjectId("5574bdf3c705777157a515ac"),
        "username" : "spring",
        "url" : "webinglin.github.io",
        "tags" : [
                "spring",
                "framework"
        ],
        "likes" : 777,
        "author" : "linwenbin"
}
{
        "_id" : ObjectId("5574cefa192e9dda0925e39e"),
        "username" : "springMVC",
        "likes" : 888
}
{
        "_id" : ObjectId("5574bdd2c705777157a515ab"),
        "username" : "redis",
        "url" : "webinglin.github.io",
        "tags" : [
                "redis",
                "database",
                "nosql"
        ],
        "likes" : 888,
        "author" : "linwenbin"
}
{
        "_id" : ObjectId("5574cef5192e9dda0925e39d"),
        "username" : "mongodb",
        "likes" : 999
}
{
        "_id" : ObjectId("5574bdabc705777157a515aa"),
        "username" : "mongo",
        "url" : "webinglin.github.io",
        "tags" : [
                "mongodb",
                "database",
                "nosql"
        ],
        "likes" : 999,
        "author" : "linwenbin"
}
>

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转载请注明出处！ 原文地址： http://webinglin.github.io

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2015-06-07
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