對于文檔的更新除替換外，針對某個或多個文檔只需要部分更新可使用原子的更新修改器，能夠高效的進行文檔更新。更新修改器是中特殊的鍵，
用來指定復雜的操作，比如增加、刪除或者調整鍵，還可能是操作數組或者內嵌文檔。
1.$inc
這個修改器干什么使的呢？看看下面示例的具體操作后的結果即可知道。
示例文檔：{"uid":"201203","type":"1",size:10}
> db.b.insert({"uid":"201203","type":"1",size:10})> db.b.find(){ "_id" : ObjectId("5003b6135af21ff428dafbe6"), "uid" : "201203", "type" : "1","size" : 10 }> db.b.update({"uid" : "201203"},{"$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$inc可以對文檔的某個值為數字型（只能為滿足要求的數字）的鍵進行增減的操作。
（這里有個問題：上篇中說到更新默認只對滿足條件的記錄集中第一個文檔進行更新，那么使用$inc修改器之后，還是一樣嗎？）
2.$set
用來指定一個鍵并更新鍵值，若鍵不存在并創建。來看看下面的效果：
> db.a.findOne({"uid" : "20120002","type" : "3"}){ "_id" : ObjectId("500216de81b954b6161a7d8f"), "desc" : "hello world2!", "num": 40, "sname" : "jk", "type" : "3", "uid" : "20120002" }--size鍵不存在的場合> db.a.update({"uid" : "20120002","type" : "3"},{"$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"} 對于內嵌的文檔，$set又是如何進行更新的內嵌的文檔的呢，請看下面的示例：
示例文檔：{"name":"toyota","type":"suv","size":{"height":10,"width":5,"length":15}}
> db.c.findOne({"name":"toyota"}){ "_id" : ObjectId("5003be465af21ff428dafbe7"), "name" : "toyota", "type" : "suv", "size" : { "height" : 10, "width" : 5, "length" : 15 }}> db.c.update({"name":"toyota"},{"$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"},{"$set":{"size.width":7}})> db.c.findOne({"name":"toyota"}){ "_id" : ObjectId("5003be465af21ff428dafbe7"), "name" : "toyota", "type" : "suv", "size" : { "height" : 8, "width" : 7, "length" : 15 }}可見：對于內嵌文檔在使用$set更新時，使用"."連接的方式。
3.$unset
從字面就可以看出其意義，主要是用來刪除鍵。
示例操作效果如下：
> db.a.update({"uid" : "20120002","type" : "3"},{"$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1、0、-1或者具體的字符串等都是可以刪除該目標鍵。
4.數組修改器--$push
示例操作效果如下：
> db.c.find(){ "_id" : ObjectId("5003be465af21ff428dafbe7"), "name" : "toyota", "type" : "suv","size" : { "height" : 8, "width" : 7, "length" : 15 } }--先push一個當前文檔中不存在的鍵title> db.c.update({"name" : "toyota"},{$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：$push--向文檔的某個數組類型的鍵添加一個數組元素，不過濾重復的數據。添加時鍵存在，要求鍵值類型必須是數組；鍵不存在，則創建數組類型的鍵。
5.數組修改器--$ne/$addToSet
主要給數組類型鍵值添加一個元素時，避免在數組中產生重復數據，$ne在有些情況是不通行的。
> 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
$pop從數組的頭或者尾刪除數組中的元素，示例如下：
{ "_id" : ObjectId("5003be465af21ff428dafbe7"), "name" : "toyota", "size" : { "height" : 8, "width" : 7, "length" : 15 }, "title" : [ "t1", "t2", "t3", "t4" ],"type" : "suv" }--從數組的尾部刪除 1> db.c.update({"name" : "toyota"},{$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" } $pull從數組中刪除滿足條件的元素，示例如下：{ "_id" : ObjectId("5003be465af21ff428dafbe7"), "name" : "toyota", "size" : { "height" : 8, "width" : 7, "length" : 15 }, "title" : [ "t1", "t2", "t2", "t3" ],"type" : "suv" } > db.c.update({"name" : "toyota"},{$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
在需要對數組中的值進行操作的時候，可通過位置或者定位操作符（"$"）.數組是0開始的，可以直接將下標作為鍵來選擇元素。
示例如下：
{"uid":"001",comments:[{"name":"t1","size":10},{"name":"t2","size":12}]}> db.c.find({"uid":"001"}){ "_id" : ObjectId("5003da405af21ff428dafbe8"), "uid" : "001", "comments" : [ {"name" : "t1", "size" : 10 }, { "name" : "t2", "size" : 12 } ] }> db.c.update({"uid":"001"},{$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 } ] }--若為多個文檔滿足條件，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為基礎創建一個新的文檔，如果找到匹配的文檔就正常的更新。
使用upsert，既可以避免競態問題，也可以減少代碼量（update的第三個參數就表示這個upsert，參數為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.可以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。否則，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" }
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