mongo中使用$type查询字段的BSON类型

$type操作符用来查询某个字段是否是的指定BSON类型。当文档的数据类型是高度的非结构化时，这非常的有用
{ field: { $type: <BSON type> } }，你可以通过数组或别名来指定BSON的type
{ field: { $type: [ <BSON type1> , <BSON type2>, ... ] } }，这将匹配数组中BSON类型的任意一个

BSON type总结（version 3.2）

3.2版本可以使用别名或数字来指定BSON类型，在3.2之前的版本只能使用数字来匹配。

Type	Number	Alias	Notes
Double	1	“double”
String	2	“string”
Object	3	“object”
Array	4	“array”
Binary data	5	“binData”
Undefined	6	“undefined”	废弃
ObjectId	7	“objectId”
Boolean	8	“bool”
Date	9	“date”
Null	10	“null”
RegularExpression	11	“regex”
DBPointer	12	“dbPointer”
JavaScript	13	“javascript”
Sysmbol	14	“symbol”	废弃
JavaScript(with scope)	15	“javascriptWithScope”
32-bit integer	16	“int”
Timestamp	17	“timestamp”
64-bit integer	18	“long”
Decimal128	19	“decimal”	3.4版本新增
Min key	-1	“minKey”
Max Key	127	“maxKey”

示例

源数据

[
      { "_id" : 1, address : "2030 Martian Way", zipCode : "90698345" },
      { "_id" : 2, address: "156 Lunar Place", zipCode : 43339374 },
      { "_id" : 3, address : "2324 Pluto Place", zipCode: NumberLong(3921412) },
      { "_id" : 4, address : "55 Saturn Ring" , zipCode : NumberInt(88602117) }
]

查询zipCode字段是string的：

db.addressBook.find( { "zipCode" : { $type : 2 } } );
//等价于
db.addressBook.find( { "zipCode" : { $type : "string" } } );

//返回结果
{ "_id" : 1, "address" : "2030 Martian Way", "zipCode" : "90698345" }

zipCode的BSON类型是double的：

db.addressBook.find( { "zipCode" : { $type : 1 } } )
//等价于
db.addressBook.find( { "zipCode" : { $type : "double" } } )
//返回结果
{ "_id" : 2, "address" : "156 Lunar Place", "zip" : 43339374 }

使用number类型别名匹配BSON类型是double``int或long的：

db.addressBook.find( { "zipCode" : { $type : "number" } } )
//返回结果
{ "_id" : 2, address : "156 Lunar Place", zipCode : 43339374 }
{ "_id" : 3, address : "2324 Pluto Place", zipCode: NumberLong(3921412) }
{ "_id" : 4, address : "55 Saturn Ring" , zipCode : 88602117 }

示例2

源数据

[
      { "_id" : 1, name : "Alice King" , classAverage : 87.333333333333333 },
      { "_id" : 2, name : "Bob Jenkins", classAverage : "83.52" },
      { "_id" : 3, name : "Cathy Hart", classAverage: "94.06" },
      { "_id" : 4, name : "Drew Williams" , classAverage : 93 }
   ]

查询classAverage字段是BSON类型string或double的：

db.grades.find( { "classAverage" : { $type : [ 2 , 1 ] } } );
//等价于
db.grades.find( { "classAverage" : { $type : [ "string" , "double" ] } } );
//返回结果
{ "_id" : 1, name : "Alice King" , classAverage : 87.333333333333333 }
{ "_id" : 2, name : "Bob Jenkins", classAverage : "83.52" }
{ "_id" : 3, name : "Cathy Hart", classAverage: "94.06" }