mongoDB修改字段类型：string转decimal

将test表中的num_string字段从String转换到decimal:

db.test.find().forEach(function(x){x.num_string=NumberDecimal(Number(x.num_string));db.test.save(x);})

为了严谨，只转换字段是特定类型的数据

find指定数据类型的字段：

db.test.find({‘num_string’ : { $type : 16 }})

将指定数据类型的字段转换：

db.test.find({‘num_string’ : { $type : 2 }}).forEach(function(x){x.num_string=NumberDecimal(Number(x.num_string));db.test.save(x);})

mongodb3.4字段类型编号:

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