对于文档的更新除替换外,针对某个或多个文档只需要部分更新可使用原子的更新修改器,能够高效的进行文档更新。更新修改器是中特殊的键,
用来指定复杂的操作,比如增加、删除或者调整键,还可能是操作数组或者内嵌文档。

1.$inc
--------------------------------------------------------------------------
这个修改器干什么使的呢?看看下面示例的具体操作后的结果即可知道。

示例文档:

{"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 }

得出结论:修改器$inc可以对文档的某个值为数字型(只能为满足要求的数字)的键进行增减的操作。
(这里有个问题:上篇中说到更新默认只对满足条件的记录集中第一个文档进行更新,那么使用$inc修改器之后,还是一样吗?)

2.$set
-------------------------------------------------------------------
用来指定一个键并更新键值,若键不存在并创建。来看看下面的效果:

> db.a.findOne({"uid" : "20120002","type" : "3"}) 
{ "_id" : ObjectId("500216de81b954b6161a7d8f"), "desc" : "hello world2!", "num" 
: 40, "sname" : "jk", "type" : "3", "uid" : "20120002" } 
--size键不存在的场合 
> db.a.update({"uid" : "20120002","type" : "3"},{"$set":{"size":10}}) 
> db.a.findOne({"uid" : "20120002","type" : "3"}) 
{ "_id" : ObjectId("500216de81b954b6161a7d8f"), "desc" : "hello world2!", "num" 
: 40, "size" : 10, "sname" : "jk", "type" : "3", "uid" : "20120002" } 
--sname键存在的场合 
> db.a.update({"uid" : "20120002","type" : "3"},{"$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" } 
--可改变键的值类型 
> 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" 
}

对于内嵌的文档,$set又是如何进行更新的内嵌的文档的呢,请看下面的示例:
示例文档:

{"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 
        } 
}

可见:对于内嵌文档在使用$set更新时,使用"."连接的方式。


3.$unset
----------------------------------------------------------------
从字面就可以看出其意义,主要是用来删除键。
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" 
}

得出结论:使用修改器$unset时,不论对目标键使用1、0、-1或者具体的字符串等都是可以删除该目标键。

4.数组修改器--$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一个当前文档中不存在的键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一个值

> 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一个值

> 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" }

--再向一个已经存在的键值非数组类型的键push一个值

> 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

得出结论:$push--向文档的某个数组类型的键添加一个数组元素,不过滤重复的数据。添加时键存在,要求键值类型必须是数组;键不存在,则创建数组类型的键。

5.数组修改器--$ne/$addToSet
---------------------------------------------------------------------
主要给数组类型键值添加一个元素时,避免在数组中产生重复数据,$ne在有些情况是不通行的。

> 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.数组修改器--$pop、$pull
------------------------------------------------------------
$pop从数组的头或者尾删除数组中的元素,示例如下:

{ "_id" : ObjectId("5003be465af21ff428dafbe7"), "name" : "toyota", "size" : { "height" : 8, 
 "width" : 7, "length" : 15 }, "title" : [ "t1", "t2", "t3", "t4" ],"type" : "suv" }

--从数组的尾部删除 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" }

--从数组的头部 -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" }

--从数组的尾部删除 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从数组中删除满足条件的元素,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.数组的定位修改器
-------------------------------------------------------------------
在需要对数组中的值进行操作的时候,可通过位置或者定位操作符("$").数组是0开始的,可以直接将下标作为键来选择元素。
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 } ] }

--若为多个文档满足条件,则只更新第一个文档。

8.upsert
-----------------------------------------------------------------
upsert是一种特殊的更新。当没有符合条件的文档,就以这个条件和更新文档为基础创建一个新的文档,如果找到匹配的文档就正常的更新。
使用upsert,既可以避免竞态问题,也可以减少代码量(update的第三个参数就表示这个upsert,参数为true时)

> 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函数
-----------------------------------------------------------------
1.可以在文档不存在的时候插入,存在的时候更新,只有一个参数文档。
2.要是文档含有"_id",会调用upsert。否则,会调用插入。

> db.a.find() 
{ "_id" : ObjectId("50026affdeb4fa8d154f8572"), "desc" : "hello world1!", "num": 50, 
 "sname" : "jk", "type" : "1", "uid" : "20120002" } 
> var o = db.a.findOne() 
> o.num = 55 
55 
> 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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