The table below contains type mapping rules that are used to map BSON types to .NET types.

BSON Type	MongoDBType	SQL Engine Column	.NET Data Type
Double	Double	DOUBLE	Double
Double in a column declared SINGLE or FLOAT4 (CREATE TABLE, EnsureCreated)	Double	SINGLE	Single
String	String	VARCHAR	String
32-bit integer	Integer	INT	Int32
32-bit integer in a column declared TINYINT or SMALLINT (CREATE TABLE, EnsureCreated)	Integer	TINYINT, SMALLINT	Byte, Int16
64-bit integer	Long	INT64	Int64
Decimal128	Decimal128	DECIMAL128	String by default; Decimal or Double by Decimal128 Mapping
Boolean	Boolean	BOOLEAN	Boolean
Date	Date	DATETIME	DateTime, Kind by DateTime Kind (Utc by default)
ObjectId	Oid	OID	String (24 hexadecimal digits)
Binary data, subtype 4 (or 3, by Guid Format)	Uuid	UUID	Guid
Other binary data	Binary	part columns .base64 and .subType	String
Date with offset, stored by DateTimeOffset Format	DateTimeOffset	DATETIMEOFFSET	DateTimeOffset
Embedded document	Object	A column for each nested field; one VARCHAR with JSON with Complex As String or Json Fields	String (JSON)
Array	Array	A column per element (tags.0); one VARCHAR with JSON with Complex As String or Json Fields	String (JSON)
Regular expression	Regex	Part columns .pattern and .options	String
JavaScript	Code	Part column .$code	String
JavaScript with scope	ScopeCode	Part columns .$code, .$scope	String
Timestamp	TimeStamp	Part columns .t and .i	String; parts Int32
Null	Null	MNULL	String (the value is DBNull)
MinKey, MaxKey	MinKey, MaxKey	MINKEY, MAXKEY	String

Notes:

• Uuid and DateTimeOffset are not BSON types; they describe how the provider reads a binary Guid and a stored DateTimeOffset, respectively.
• A column created by CREATE TABLE or EF Core EnsureCreated retains its declared type in the collection schema. TINYINT, SMALLINT, and SINGLE columns are read as Byte, Int16, and Single, respectively (GetDataTypeName returns TINYINT, SMALLINT, SINGLE). The values are stored as 32-bit integers and doubles. A stored value that doesn't fit the declared type is returned by GetValue as stored, while GetByte, GetInt16, and GetFloat throw an InvalidCastException with the message: "The value 300 of the column "b" can't be converted to Byte".
• DateTimeOffset Format: DateTime (default; a BSON date, with the offset lost), Document ({DateTime, Ticks, Offset} as the official MongoDB driver writes it), Array ([ticks, offset in minutes]), or String (ISO 8601). All these formats are supported for reading. In SQL, such values are compared and sorted by the instant.
• Guid Format: Uuid (default, subtype 4), Subtype3Rfc, Subtype3Guid, Subtype3Reversed (Java byte order), or String. Subtype 4 and text are supported for reading regardless of the format. In SQL, a UUID column compares against the text representation of the Guid, regardless of letter case.
• Undefined, DBPointer, and Symbol are deprecated in MongoDB and are not supported. Reading them raises the "Unknown BSON type" error.
• Decimal128 Mapping=Decimal rounds values to 28-29 digits; NaN, Infinity, and out-of-range values throw an OverflowException. Double preserves NaN and Infinity.
• Decimal128 values are sorted numerically in SQL (1.5 equals 1.50).
• With Complex As String, the JSON uses relaxed Extended JSON: numbers are represented as plain values (5, not {"$numberLong":"5"}), while ObjectId and date values retain the {"$oid": ...} and {"$date": ...} formats.

Parameter Types

.NET Data Type	BSON Type Written
Byte, SByte, Int16, UInt16, Int32, UInt32	32-bit integer
Int64, UInt64	64-bit integer
Single, Double	Double
Decimal	Decimal128
Boolean	Boolean
DateTime	Date; a DateTime of Unspecified kind is taken as DateTime Kind
DateTimeOffset	By DateTimeOffset Format
Guid	By Guid Format (binary subtype 4 by default)
String	String; ObjectId when MongoDBType=Oid
Byte[] with MongoDBType=Binary	Binary data, subtype 0
MongoDBDocument	Embedded document
Null	Null

Arrays can't be passed as parameters. A Byte[] value requires MongoDBType=Binary to be set explicitly.