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"}