mongodb_修改器（$inc/$set/$unset/$push/$pop/upsert...

對於文檔的更新除替換外，針對某個或多個文檔只須要部分更新可以使用原子的更新修改器，可以高效的進行文檔更新。更新修改器是中特殊的鍵，
用來指定複雜的操做，好比增長、刪除或者調整鍵，還多是操做數組或者內嵌文檔。

1.$inc
--------------------------------------------------------------------------
這個修改器幹什麼使的呢？看看下面示例的具體操做後的結果便可知道。

示例文檔：{"uid":"201203","type":"1",size:10}

> db.b.insert({"uid":"201203","type":"1",size:10})
> db.b.find()
{ "_id" : ObjectId("5003b6135af21ff428dafbe6"), "uid" : "201203", "type" : "1",
"size" : 10 }
> db.b.update({"uid" : "201203"},{"$inc":{"size" : 1}})
> db.b.find()
{ "_id" : ObjectId("5003b6135af21ff428dafbe6"), "uid" : "201203", "type" : "1",
"size" : 11 }
> db.b.update({"uid" : "201203"},{"$inc":{"size" : 2}})
> db.b.find()
{ "_id" : ObjectId("5003b6135af21ff428dafbe6"), "uid" : "201203", "type" : "1",
"size" : 13 }
> db.b.update({"uid" : "201203"},{"$inc":{"size" : -1}})
> db.b.find()
{ "_id" : ObjectId("5003b6135af21ff428dafbe6"), "uid" : "201203", "type" : "1",
"size" : 12 }

得出結論：修改器$inc能夠對文檔的某個值爲數字型（只能爲知足要求的數字）的鍵進行增減的操做。
（這裏有個問題：上篇中說到更新默認只對知足條件的記錄集中第一個文檔進行更新，那麼使用$inc修改器以後，仍是同樣嗎？）

2.$set
-------------------------------------------------------------------
用來指定一個鍵並更新鍵值，若鍵不存在並建立。來看看下面的效果：

> db.a.findOne({"uid" : "20120002","type" : "3"})
{ "_id" : ObjectId("500216de81b954b6161a7d8f"), "desc" : "hello world2!", "num"
: 40, "sname" : "jk", "type" : "3", "uid" : "20120002" }
--size鍵不存在的場合
> db.a.update({"uid" : "20120002","type" : "3"},{"$set":{"size":10}})
> db.a.findOne({"uid" : "20120002","type" : "3"})
{ "_id" : ObjectId("500216de81b954b6161a7d8f"), "desc" : "hello world2!", "num"
: 40, "size" : 10, "sname" : "jk", "type" : "3", "uid" : "20120002" }
--sname鍵存在的場合
> db.a.update({"uid" : "20120002","type" : "3"},{"$set":{"sname":"ssk"}})
> db.a.find()
{ "_id" : ObjectId("500216de81b954b6161a7d8f"), "desc" : "hello world2!", "num"
: 40, "size" : 10, "sname" : "ssk", "type" : "3", "uid" : "20120002" }
{ "_id" : ObjectId("50026affdeb4fa8d154f8572"), "desc" : "hello world1!", "num"
: 50, "sname" : "jk", "type" : "1", "uid" : "20120002" }
--可改變鍵的值類型
> db.a.update({"uid" : "20120002","type" : "3"},{"$set":{"sname":["java",".net","c++"]}})
> db.a.findOne({"uid" : "20120002","type" : "3"})
{
        "_id" : ObjectId("500216de81b954b6161a7d8f"),
        "desc" : "hello world2!",
        "num" : 40,
        "size" : 10,
        "sname" : [
                "java",
                ".net",
                "c++"
        ],
        "type" : "3",
        "uid" : "20120002"
}

對於內嵌的文檔，$set又是如何進行更新的內嵌的文檔的呢，請看下面的示例：
示例文檔：{"name":"toyota","type":"suv","size":{"height":10,"width":5,"length":15}}

> db.c.findOne({"name":"toyota"})
{
        "_id" : ObjectId("5003be465af21ff428dafbe7"),
        "name" : "toyota",
        "type" : "suv",
        "size" : {
                "height" : 10,
                "width" : 5,
                "length" : 15
        }
}
> db.c.update({"name":"toyota"},{"$set":{"size.height":8}})
> db.c.findOne({"name":"toyota"})
{
        "_id" : ObjectId("5003be465af21ff428dafbe7"),
        "name" : "toyota",
        "type" : "suv",
        "size" : {
                "height" : 8,
                "width" : 5,
                "length" : 15
        }
}
> db.c.update({"name":"toyota"},{"$set":{"size.width":7}})
> db.c.findOne({"name":"toyota"})
{
        "_id" : ObjectId("5003be465af21ff428dafbe7"),
        "name" : "toyota",
        "type" : "suv",
        "size" : {
                "height" : 8,
                "width" : 7,
                "length" : 15
        }
}
可見：對於內嵌文檔在使用$set更新時，使用"."鏈接的方式。

3.$unset
----------------------------------------------------------------
從字面就能夠看出其意義，主要是用來刪除鍵。
示例操做效果以下：

> db.a.update({"uid" : "20120002","type" : "3"},{"$unset":{"sname":1}})
> db.a.findOne({"uid" : "20120002","type" : "3"})
{
        "_id" : ObjectId("500216de81b954b6161a7d8f"),
        "desc" : "hello world2!",
        "num" : 40,
        "size" : 10,
        "type" : "3",
        "uid" : "20120002"
}
> db.a.update({"uid" : "20120002","type" : "3"},{"$unset":{"num":0}})
> db.a.findOne({"uid" : "20120002","type" : "3"})
{
        "_id" : ObjectId("500216de81b954b6161a7d8f"),
        "desc" : "hello world2!",
        "size" : 10,
        "type" : "3",
        "uid" : "20120002"
}
> db.a.update({"uid" : "20120002","type" : "3"},{"$unset":{"size":-1}})
> db.a.findOne({"uid" : "20120002","type" : "3"})
{
        "_id" : ObjectId("500216de81b954b6161a7d8f"),
        "desc" : "hello world2!",
        "type" : "3",
        "uid" : "20120002"
}
> db.a.update({"uid" : "20120002","type" : "3"},{"$unset":{"desc":"sssssss"}})
> db.a.findOne({"uid" : "20120002","type" : "3"})
{
        "_id" : ObjectId("500216de81b954b6161a7d8f"),
        "type" : "3",
        "uid" : "20120002"
}

得出結論：使用修改器$unset時，不論對目標鍵使用一、0、-1或者具體的字符串等都是能夠刪除該目標鍵。

4.數組修改器--$push
------------------------------------------------------------------
示例操做效果以下：
> db.c.find()
{ "_id" : ObjectId("5003be465af21ff428dafbe7"), "name" : "toyota", "type" : "suv",
"size" : { "height" : 8, "width" : 7, "length" : 15 } }

--先push一個當前文檔中不存在的鍵title
> db.c.update({"name" : "toyota"},{$push:{"title":"t1"}})
> db.c.find()
{ "_id" : ObjectId("5003be465af21ff428dafbe7"), "name" : "toyota", "size" : { "height" : 8,
 "width" : 7, "length" : 15 }, "title" : [ "t1" ], "type" : "suv" }
 
--再向title中push一個值
> db.c.update({"name" : "toyota"},{$push:{"title":"t2"}})
> db.c.find()
{ "_id" : ObjectId("5003be465af21ff428dafbe7"), "name" : "toyota", "size" : { "height" : 8,
 "width" : 7, "length" : 15 }, "title" : [ "t1", "t2" ], "type" : "suv" }

--再向title中push一個值
> db.c.update({"name" : "toyota"},{$push:{"title":"t2"}})
> db.c.find()
{ "_id" : ObjectId("5003be465af21ff428dafbe7"), "name" : "toyota", "size" : { "height" : 8,
 "width" : 7, "length" : 15 }, "title" : [ "t1", "t2", "t2" ], "type" : "suv" }

--再向一個已經存在的鍵值非數組類型的鍵push一個值
> db.c.update({"name" : "toyota"},{$push:{"size.height":10}})
Cannot apply $push/$pushAll modifier to non-array
> db.c.update({"name" : "toyota"},{$push:{"name":"ddddddd"}})
Cannot apply $push/$pushAll modifier to non-array

得出結論：$push--向文檔的某個數組類型的鍵添加一個數組元素，不過濾重複的數據。添加時鍵存在，要求鍵值類型必須是數組；鍵不存在，則建立數組類型的鍵。

5.數組修改器--$ne/$addToSet
---------------------------------------------------------------------
主要給數組類型鍵值添加一個元素時，避免在數組中產生重複數據，$ne在有些狀況是不通行的。

> db.c.update({"title" : {$ne:"t2"}},{$push:{"title":"t2"}})
> db.c.find()
{ "_id" : ObjectId("5003be465af21ff428dafbe7"), "name" : "toyota", "size" : { "height" : 8,
 "width" : 7, "length" : 15 }, "title" : [ "t1", "t2", "t2" ], "type" : "suv" }

> db.c.update({"name" : "toyota"},{$addToSet:{"title":"t2"}})
> db.c.find()
{ "_id" : ObjectId("5003be465af21ff428dafbe7"), "name" : "toyota", "size" : { "height" : 8,
 "width" : 7, "length" : 15 }, "title" : [ "t1", "t2", "t2" ], "type" : "suv" }

6.數組修改器--$pop、$pull
------------------------------------------------------------
$pop從數組的頭或者尾刪除數組中的元素，示例以下：
{ "_id" : ObjectId("5003be465af21ff428dafbe7"), "name" : "toyota", "size" : { "height" : 8,
 "width" : 7, "length" : 15 }, "title" : [ "t1", "t2", "t3", "t4" ],"type" : "suv" }

--從數組的尾部刪除 1
> db.c.update({"name" : "toyota"},{$pop:{"title":1}})
> db.c.find()
{ "_id" : ObjectId("5003be465af21ff428dafbe7"), "name" : "toyota", "size" : { "height" : 8,
 "width" : 7, "length" : 15 }, "title" : [ "t1", "t2", "t3" ], "type" : "suv" }
--從數組的頭部 -1
> db.c.update({"name" : "toyota"},{$pop:{"title":-1}})
> db.c.find()
{ "_id" : ObjectId("5003be465af21ff428dafbe7"), "name" : "toyota", "size" : { "height" : 8,
 "width" : 7, "length" : 15 }, "title" : [ "t2", "t3" ], "type" : "suv" }
--從數組的尾部刪除 0
> db.c.update({"name" : "toyota"},{$pop:{"title":0}})
> db.c.find()
{ "_id" : ObjectId("5003be465af21ff428dafbe7"), "name" : "toyota", "size" : { "height" : 8,
 "width" : 7, "length" : 15 }, "title" : [ "t2" ], "type" : "suv" }
 
$pull從數組中刪除知足條件的元素，示例以下：
{ "_id" : ObjectId("5003be465af21ff428dafbe7"), "name" : "toyota", "size" : { "height" : 8,
 "width" : 7, "length" : 15 }, "title" : [ "t1", "t2", "t2", "t3" ],"type" : "suv" }
 
> db.c.update({"name" : "toyota"},{$pull:{"title":"t2"}})
> db.c.find()
{ "_id" : ObjectId("5003be465af21ff428dafbe7"), "name" : "toyota", "size" : { "height" : 8,
 "width" : 7, "length" : 15 }, "title" : [ "t1", "t3" ], "type" : "suv" }
 
7.數組的定位修改器
-------------------------------------------------------------------
在須要對數組中的值進行操做的時候，可經過位置或者定位操做符（"$"）.數組是0開始的，能夠直接將下標做爲鍵來選擇元素。
示例以下：
{"uid":"001",comments:[{"name":"t1","size":10},{"name":"t2","size":12}]}

> db.c.find({"uid":"001"})
{ "_id" : ObjectId("5003da405af21ff428dafbe8"), "uid" : "001", "comments" : [ {
"name" : "t1", "size" : 10 }, { "name" : "t2", "size" : 12 } ] }
> db.c.update({"uid":"001"},{$inc:{"comments.0.size":1}})
> db.c.find({"uid":"001"})
{ "_id" : ObjectId("5003da405af21ff428dafbe8"), "uid" : "001", "comments" : [ {
"name" : "t1", "size" : 11 }, { "name" : "t2", "size" : 12 } ] }
> db.c.update({"comments.name":"t1"},{$set:{"comments.$.size":1}})
> db.c.find({"uid":"001"})
{ "_id" : ObjectId("5003da405af21ff428dafbe8"), "uid" : "001", "comments" : [ {
"name" : "t1", "size" : 1 }, { "name" : "t2", "size" : 12 } ] }

--若爲多個文檔知足條件，則只更新第一個文檔。

8.upsert
-----------------------------------------------------------------
upsert是一種特殊的更新。當沒有符合條件的文檔，就以這個條件和更新文檔爲基礎建立一個新的文檔，若是找到匹配的文檔就正常的更新。
使用upsert，既能夠避免競態問題，也能夠減小代碼量（update的第三個參數就表示這個upsert，參數爲true時）

> db.c.remove()
> db.c.update({"size":11},{$inc:{"size":3}})
> db.c.find()
> db.c.update({"size":11},{$inc:{"size":3}},false)
> db.c.find()
> db.c.update({"size":11},{$inc:{"size":3}},true)
> db.c.find()
{ "_id" : ObjectId("5003ded6c28f67507a6df1de"), "size" : 14 }

9.save函數-----------------------------------------------------------------1.能夠在文檔不存在的時候插入，存在的時候更新，只有一個參數文檔。2.要是文檔含有"_id"，會調用upsert。不然，會調用插入。> db.a.find(){ "_id" : ObjectId("50026affdeb4fa8d154f8572"), "desc" : "hello world1!", "num": 50, "sname" : "jk", "type" : "1", "uid" : "20120002" }> var o = db.a.findOne()> o.num = 5555> db.a.save(o)> db.a.find(){ "_id" : ObjectId("50026affdeb4fa8d154f8572"), "desc" : "hello world1!", "num": 55, "sname" : "jk", "type" : "1", "uid" : "20120002" }