MongoDB學習札記第四篇之Query

時間  2019-12-10
標籤 mongodb 學習 札記 第四 query 欄目 MongoDB 简体版
原文   原文鏈接

系列專題http://www.codefrom.com/p/mongodbgit

查詢條件github

首先往數據庫集合裏面插入幾條數據。
測試數據：web

> 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() 方法是對查詢結果進行格式化
查詢的時候能夠帶上查詢條件,那具體的查詢條件怎麼使用？
等於
等於操做直接使用 {key:value} 這樣的文檔形式便可redis

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

大於
語法： {key : {$gt:value} }spring

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

大於等於
語法： {key : {$gte:value} }sql

> 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" }

小於
語法：　{key : {$lt:value} }mongodb

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

小於等於數據庫

語法：　{key : {$lte:value}}數組

> 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" }

不等於
語法： {key : {$ne:value} }nosql

> 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" }

且操做 AND
語法： {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" }

或操做 OR

語法： { $or: [ {key1: value1}, {key2:value2} ] } 將or條件的全部 {key:value} 都放在 $or 的value中（數組）

> 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" }

複雜條件查詢

如何將全部的條件都連起來用呢？

好比咱們想要這樣查詢 like>=888 && (username=」mongo」 or username=」spring」)
因爲上面的數據只有三條， 咱們知道 like>=888 只有 mongo 和 redis 這兩條數據知足條件， 後面的username=」mongo」 or username=」spring」 又有 mongo和 spring 知足條件， 這兩個and操做以後 就只剩下 mongo 這條數據知足條件了。 因此最終應該查出一條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() 其餘用法
Projection

mongodb中 projection 意味着顯示你但願看到的字段而非全部的字段都顯示,這是什麼意思呢？

好比： 咱們的測試數據裏面有那麼多的字段: username,likes,tags,author,url 而咱們常常要用到的就只有 username 和 likes 那麼就顯示這兩個字段就行了，其餘的字段就別顯示出來了。

find({},{KEY:1/0}) find的第二個參數，KEY爲要顯示或隱藏的字段，value爲1表示顯示，0表示隱藏，看着也很簡單，試一下吧


> 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

爲了更好的測試分頁的效果，新建一個集合，並插入30條數據

> 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 }

能夠發現，若是使用 limit方法的話會顯示整個集合的全部文檔。 指定了 limit 以後， 顯示具體的條數，上文中，limit(5) 表示， 顯示5條文檔。

limit方法除外，還有一個 skip 方法，skip也是接受一個整型的參數，表示查詢結果跳過多少個文檔。

例如上面插入的30條記錄中，咱們要顯示18-22條記錄，那麼就應該使用
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的組合就能作到分頁的功能了。可是若是數據量很大，理論上分頁就會變得很慢了，好比有一億條數據，要拿最後一頁。那skip的數據量就不少不少了。這樣就會變得比較慢。話說回來，有誰會看數據看到最後的幾頁？正常都是看前面幾頁數據，因此，skip和limit實現分頁是能夠接受的。

在mongodb中，若是要對查詢結果排序，那麼須要使用sort方法。sort方法接收一個文檔參數。也就是{key:value}的形式。其中，key表示要排序的字段，value的可取值爲 1 / -1 。1表示升序asc，-1表示降序desc。話很少說，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

這個是對val這個key進行逆序排序，因此value取值爲-1。 那value值爲1的話，就變成升序了。

> 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
>

那若是要對多個值進行組合排序呢？ 就比如如對於咱們最初的例子 users 集合。 要對users集合進行排序。其中 按照likes升序， 按照username降序。爲了達到咱們的效果，咱們再往users集合裏面插入兩條數據

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

下面是運行結果，注意觀察 likes爲888的兩個文檔。發現username逆序排序了。至此，說明咱們的sort實驗成功了。

> 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"
}
>

原做者：webinglin

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