MongoDB Basics II - Data Types

For MongoDB version 3.4 the data types are as follows

Type	Number	Alias	Notes
Double	1	“double”	stores floating point values
String	2	“string”	stores UTF8 text
Object	3	“object”	stores embedded documents
Array	4	“array”	can store multiple values of multiple data types
Binary data	5	“binData”	stores binary data
Undefined	6	“undefined”	Deprecated. Works like Null
ObjectId	7	“objectId”	stores the document's ID. 12 bytes, system generated
Boolean	8	“bool”	true or false
Date	9	“date”	64-bit integer representing milliseconds since 01.01.1970
Null	10	“null”
Regular Expression	11	“regex”
DBPointer	12	“dbPointer”	Deprecated.
JavaScript	13	“javascript”	stores JavaScript data without Scope
Symbol	14	“symbol”	Deprecated.
JavaScript (with scope)	15	“javascriptWithScope”	stores JavaScript data with Scope
32-bit integer	16	“int”
Timestamp	17	“timestamp”	64-bit integer. 32 bits representing seconds since 01.01.1970 + 32 bits incrementing. Unique per Mongo instance
64-bit integer	18	“long”
Decimal128	19	“decimal”	New in version 3.4  Wikipedia:Decimal128_floating-point_format
Min key	-1	“minKey”	always the lowest result in a sort
Max key	127	“maxKey”	always highest result in a sort

Each data type has a number and string alias that can be used with the $type operator to query documents by BSON type. Additionally, there is a "number" alias that corresponds to all the numeric data-types.

db.addresses.find( { "areaCode" : { $type : "number" } } )
This will find all the Documents in the addresses Collection where areaCode is numeric
 

db.addresses.find( { "areaCode" : { $type : "string" } } )
This will find all the Documents in the addresses Collection where areaCode is text

Types can be implicitly defined:
{
 screenname: "Max",                    //  string
 age: 29,                              // integer
 visible: false,                       // boolean
 subscriptions: ["mongoDB","MariaDB"]  // array
 "phone" : {"cell" : "555-123-4567",
            "office" : "555-312-6789"},// Object (embedded document)
 email: null                           // null
}

or explicitly defined:
{
 "_id" : ObjectId("5b6b9f34a1f359177d123a5a"),
 field1: NumberLong(123456) ,
 field2: NumberInt(123456789)
}