Database-First Mapping

The following table shows the property types that the Scaffold-DbContext command generates for BSON types. These types match the types that a data reader returns for the same connection and depend on the Decimal128 Mapping, Guid Format, and DateTimeOffset Format connection string parameters.

BSON Type	SQL Engine Column Type	.NET Property Type
ObjectId	OID	string
Double	DOUBLE	double
String	VARCHAR	string
32-bit integer	INT	int
32-bit integer or Double in a column declared as TINYINT, SMALLINT, or SINGLE	TINYINT, SMALLINT, SINGLE	byte, short, float
64-bit integer	INT64	long
Decimal128	DECIMAL128	Depends on Decimal128 Mapping: string (default), decimal, or double
Boolean	BOOLEAN	bool
Date	DATETIME	DateTime
Binary data, subtype 4 (or 3, depending on Guid Format)	UUID	Guid
Other binary data	BLOB	byte[]
Date with offset, stored according to DateTimeOffset Format	DATETIMEOFFSET	DateTimeOffset
Timestamp	BSONTIMESTAMP	long: seconds in the high 32 bits, increment in the low 32 bits
Regular expression, JavaScript	REGEX, JAVASCRIPT	string with the value in Extended JSON
Embedded document	-	Owned type (OwnsOne, ToJson)
Array of documents	-	Collection of owned types (OwnsMany, ToJson)
Array of values of one type	-	List<T>

Properties for fields that can be missing or null in documents are nullable, for example, int? or DateTime?.

Code-First Mapping

The following table shows how .NET property types are stored in BSON when you use the Code-First approach.

.NET Property Type	BSON Type
string	String; a single key (_id) is an ObjectId generated on insert, as are the foreign keys that reference it
int	32-bit integer
short, byte	32-bit integer; EnsureCreated declares the column as SMALLINT or TINYINT
long	64-bit integer
double	Double
float	Double; EnsureCreated declares the column as SINGLE
decimal	Decimal128
bool	Boolean
DateTime	Date; Kind depends on DateTime Kind
DateTimeOffset	Depends on DateTimeOffset Format
TimeSpan	64-bit integer (ticks)
Guid	Binary data, subtype 4 (or as specified by Guid Format)
enum	Numeric value of the enum
List<T>, T[], IList<T> of the types above	Array of values (Entity Framework Core 8–11)
Owned type, complex property in Entity Framework Core 10 and 11	Embedded document
Collection of owned types	Array of embedded documents