mongodb 修改器（$inc/$set/$unset/$push/$pop/upsert)
对于文档的更新除替换外，针对某个或多个文档只需要部分更新可使用原子的更新修改器，能够高效的进行文档更新。更新修改器是中特殊的键，
用来指定复杂的操作，比如增加、删除或者调整键，还可能是操作数组或者内嵌文档。
1.$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":"helloworld2!","num"
:40,"sname":"jk","type":"3","uid":"20120002"}
--size键不存在的场合
>db.a.update({"uid":"20120002","type":"3"},{"$set":{"size":10}})
>db.a.findOne({"uid":"20120002","type":"3"})
{"_id":ObjectId("500216de81b954b6161a7d8f"),"desc":"helloworld2!","num"
:40,"size":10,"sname":"jk","type":"3","uid":"20120002"}
--sname键存在的场合
>db.a.update({"uid":"20120002","type":"3"},{"$set":{"sname":"ssk"}})
>db.a.find()
{"_id":ObjectId("500216de81b954b6161a7d8f"),"desc":"helloworld2!","num"
:40,"size":10,"sname":"ssk","type":"3","uid":"20120002"}
{"_id":ObjectId("50026affdeb4fa8d154f8572"),"desc":"helloworld1!","num"
:50,"sname":"jk","type":"1","uid":"20120002"}
--可改变键的值类型
>db.a.update({"uid":"20120002","type":"3"},{"$set":{"sname":["Java",".net","c++"]}})
>db.a.findOne({"uid":"20120002","type":"3"})
{
"_id":ObjectId("500216de81b954b6161a7d8f"),
"desc":"helloworld2!",
"num":40,
"size":10,
"sname":[
"java",
".net",
"c++"
],
"type":"3",
"uid":"20120002"
}
对于内嵌的文档，$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"},{"$unset":{"sname":1}})
>db.a.findOne({"uid":"20120002","type":"3"})
{
"_id":ObjectId("500216de81b954b6161a7d8f"),
"desc":"helloworld2!",
"num":40,
"size":10,
"type":"3",
"uid":"20120002"
}
>db.a.update({"uid":"20120002","type":"3"},{"$unset":{"num":0}})
>db.a.findOne({"uid":"20120002","type":"3"})
{
"_id":ObjectId("500216de81b954b6161a7d8f"),
"desc":"helloworld2!",
"size":10,
"type":"3",
"uid":"20120002"
}
>db.a.update({"uid":"20120002","type":"3"},{"$unset":{"size":-1}})
>db.a.findOne({"uid":"20120002","type":"3"})
{
"_id":ObjectId("500216de81b954b6161a7d8f"),
"desc":"helloworld2!",
"type":"3",
"uid":"20120002"
}
>db.a.update({"uid":"20120002","type":"3"},{"$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}})
Cannotapply$push/$pushAllmodifiertonon-array
>db.c.update({"name":"toyota"},{$push:{"name":"ddddddd"}})
Cannotapply$push/$pushAllmodifiertonon-array
得出结论：$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":"helloworld1!","num":50,
"sname":"jk","type":"1","uid":"20120002"}
>varo=db.a.findOne()
>o.num=55
55
>db.a.save(o)
>db.a.find()
{"_id":ObjectId("50026affdeb4fa8d154f8572"),"desc":"helloworld1!","num":55,
"sname":"jk","type":"1","uid":"20120002"}