mongodb "数组的定位修改器" —— $或.

数组的定位修改器
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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。 

 

查询全部
>db.foo.find()
{"_id":ObjectId("544a3ddad4646f0c8c904965"),"a":4}
{"_id":ObjectId("544a3dc0d4646f0c8c904962"),"a":7,"name":"zhangsan2"}
{"_id":ObjectId("5463178aa14bafe4547cafc0"),"a":8,"uid":"001","comments":[{"name":"t1","size":10},{"name":"t2","size":12},{"name":"t5","size":14}]}
{"_id":ObjectId("5463179ea14bafe4547cafc1"),"a":9,"uid":"001","comments":[{"name":"t1","size":10},{"name":"t2","size":12},{"name":"t5","size":14}]}

查询a=8
>db.foo.find({a:8})
{"_id":ObjectId("5463178aa14bafe4547cafc0"),"a":8,"uid":"001","comments":[{"name":"t1","size":10},{"name":"t2","size":12},{"name":"t5","size":14}]}

更新数据中第一个元素
>db.foo.update({a:8},{$set:{"comments.0.name":"t11"}})  当更新第一个元素时，可使用$，即 comments.$.name
>db.foo.find({a:8})
{"_id":ObjectId("5463178aa14bafe4547cafc0"),"a":8,"comments":[{"name":"t11","size":10},{"name":"t2","size":12},{"name":"t5","size":14}],"uid":"001"}

更新数据中第二个元素
>db.foo.update({a:8},{$set:{"comments.1.name":"t22"}})
>db.foo.find({a:8})
{"_id":ObjectId("5463178aa14bafe4547cafc0"),"a":8,"comments":[{"name":"t11","size":10},{"name":"t22","size":12},{"name":"t5","size":14}],"uid":"001"}

>db.foo.find()
{"_id":ObjectId("544a3ddad4646f0c8c904965"),"a":4}
{"_id":ObjectId("544a3dc0d4646f0c8c904962"),"a":7,"name":"zhangsan2"}
{"_id":ObjectId("5463178aa14bafe4547cafc0"),"a":8,"comments":[{"name":"t1","size":10},{"name":"t2","size":12},{"name":"t5","size":14}],"uid":"001"
}
{"_id":ObjectId("5463179ea14bafe4547cafc1"),"a":9,"uid":"001","comments":[{"name":"t1","size":10},{"name":"t2","size":12},{"name":"t5","size":14}]}

>db.foo.update({$set:{"comments.1.name":"t22"}})
assertfailed:needanobject  -——提示只能更新一个对象中的数据元素
Error:PrintingStackTrace
atprintStackTrace(src/mongo/shell/utils.js:37:15)
atdoassert(src/mongo/shell/assert.js:6:5)
atassert(src/mongo/shell/assert.js:14:5)
atDBCollection.update(src/mongo/shell/collection.js:220:5)
at(shell):1:8
WedNov1216:25:52.234assertfailed:needanobjectatsrc/mongo/shell/assert.js:7

>db.foo.update({},{$set:{"comments.1.name":"t22"}})    --默认更新一条记录，这种方式虽然不报错，但是不对

>db.foo.find({})
{"_id":ObjectId("544a3dc0d4646f0c8c904962"),"a":7,"name":"zhangsan2"}
{"_id":ObjectId("5463178aa14bafe4547cafc0"),"a":8,"comments":[{"name":"t1","size":10},{"name":"t2","size":12},{"name":"t5","size":14}],"uid":"001"}
{"_id":ObjectId("5463179ea14bafe4547cafc1"),"a":9,"uid":"001","comments":[{"name":"t1","size":10},{"name":"t2","size":12},{"name":"t5","size":14}]}
{"_id":ObjectId("544a3ddad4646f0c8c904965"),"a":4,"comments":{"1":{"name":"t22"}}}

>db.foo.update({},{$set:{"comments.1.name":"t222"}},0,1)--更全部的查询记录，这种方式也不报错，但是也不对的
>db.foo.find({})
{"_id":ObjectId("5463178aa14bafe4547cafc0"),"a":8,"comments":[{"name":"t1","size":10},{"name":"t222","size":12},{"name":"t5","size":14}],"uid":"001"}
{"_id":ObjectId("5463179ea14bafe4547cafc1"),"a":9,"comments":[{"name":"t1","size":10},{"name":"t222","size":12},{"name":"t5","size":14}],"uid":"001"}
{"_id":ObjectId("544a3ddad4646f0c8c904965"),"a":4,"comments":{"1":{"name":"t222"}}}
{"_id":ObjectId("544a3dc0d4646f0c8c904962"),"a":7,"comments":{"1":{"name":"t222"}},"name":"zhangsan2"}
>

 

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> db.foo.find()
{ "_id" : ObjectId("544a3ddad4646f0c8c904965"), "a" : 4 }
{ "_id" : ObjectId("544a3dd0d4646f0c8c904963"), "a" : "2.3", "name" : "zhangsan" }
{ "_id" : ObjectId("544a3dc0d4646f0c8c904962"), "a" : 7, "name" : "zhangsan2" }
{ "_id" : ObjectId("544a3dd5d4646f0c8c904964"), "a" : 3, "title" : [  2,  3,  4,  5 ] }

> db.foo.update({a:3},{$push:{title:6}})
> db.foo.find()
{ "_id" : ObjectId("544a3ddad4646f0c8c904965"), "a" : 4 }
{ "_id" : ObjectId("544a3dd0d4646f0c8c904963"), "a" : "2.3", "name" : "zhangsan" }
{ "_id" : ObjectId("544a3dc0d4646f0c8c904962"), "a" : 7, "name" : "zhangsan2" }
{ "_id" : ObjectId("544a3dd5d4646f0c8c904964"), "a" : 3, "title" : [  2,  3,  4,  5,  6 ] }

> db.foo.update({},{$push:{title:6}},0,1)
> db.foo.find()
{ "_id" : ObjectId("544a3ddad4646f0c8c904965"), "a" : 4, "title" : [  6 ] }
{ "_id" : ObjectId("544a3dd0d4646f0c8c904963"), "a" : "2.3", "name" : "zhangsan", "title" : [  6 ] }
{ "_id" : ObjectId("544a3dc0d4646f0c8c904962"), "a" : 7, "name" : "zhangsan2", "title" : [  6 ] }
{ "_id" : ObjectId("544a3dd5d4646f0c8c904964"), "a" : 3, "title" : [  2,  3,  4,  5,  6,  6 ] }

 

> db.foo.find()

{ "_id" : ObjectId("544a3ddad4646f0c8c904965"), "a" : 4, "title" : [6,6 ] }
{ "_id" : ObjectId("544a3dd0d4646f0c8c904963"), "a" : "2.3", "name" : "zhangsan", "title" : [6,6 ] }
{ "_id" : ObjectId("544a3dc0d4646f0c8c904962"), "a" : 7, "name" : "zhangsan2", "title" : [6,6 ] }
{ "_id" : ObjectId("544a3dd5d4646f0c8c904964"), "a" : 3, "title" : [2,3,4,5,6,6,6 ] }

> db.foo.update({a:3},{$set:{"title.$":22}})
Cannot apply the positional operator without a corresponding query field containing an array.

 

> db.foo.update({a:3},{$set:{"title.0":22}})
> db.foo.find()
{ "_id" : ObjectId("544a3ddad4646f0c8c904965"), "a" : 4, "title" : [6,6 ] }
{ "_id" : ObjectId("544a3dd0d4646f0c8c904963"), "a" : "2.3", "name" : "zhangsan", "title" : [6,6 ] }
{ "_id" : ObjectId("544a3dc0d4646f0c8c904962"), "a" : 7, "name" : "zhangsan2", "title" : [6,6 ] }
{ "_id" : ObjectId("544a3dd5d4646f0c8c904964"), "a" : 3, "title" : [22,3,4,5,6,6,6 ] }

> db.foo.update({a:3},{$set:{"title.1":33}})
> db.foo.find()
{ "_id" : ObjectId("544a3ddad4646f0c8c904965"), "a" : 4, "title" : [6,6 ] }
{ "_id" : ObjectId("544a3dd0d4646f0c8c904963"), "a" : "2.3", "name" : "zhangsan", "title" : [6,6 ] }
{ "_id" : ObjectId("544a3dc0d4646f0c8c904962"), "a" : 7, "name" : "zhangsan2", "title" : [6,6 ] }
{ "_id" : ObjectId("544a3dd5d4646f0c8c904964"), "a" : 3, "title" : [22,33,4,5,6,6,6 ] }
>