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Mapping .NET Framework Data Provider Data Types to .NET Framework Data Types

The ADO.NET DataSet object is independent of any specific data source. Data in a DataSet is retrieved from a data source, and changes are persisted back to the data source using a DataAdapter. This means that when a DataAdapter fills a DataTable in a DataSet with values from a data source, the resulting data types of the columns in the DataTable are .NET Framework types rather than types specific to the .NET Framework data provider used to connect to the data source.

Likewise, when a DataReader returns a value from a data source, the resulting value is stored in a local variable that has a .NET Framework type.

For both the Fill operations of the DataAdapter and the Get methods of the DataReader, the .NET Framework type is inferred from the type returned from the .NET Framework data provider. It is recommended that you use the typed accessor methods of the DataReader when you know the specific type of the value being returned. Typed accessor methods result in better performance by returning a value as a specific .NET Framework type, eliminating the need for additional type conversion. The SqlDataReader exposes SQL Server–specific typed accessor methods if a .NET Framework type does not meet the needs of the application. SQL Server–specific typed accessor methods return objects of System.Data.SqlType.

The following tables show the inferred .NET Framework type for data types from Microsoft SQL Server, OLE DB, and ODBC. The typed accessor methods for the DataReader are also listed.

Note   Null values for any .NET Framework data provider data types are represented by DBNull.Value.

.NET Framework Data Provider for SQL Server

SQL Server type .NET Framework type .NET Framework typed accessor SqlType typed accessor
bigint Int64 GetInt64() GetSqlInt64()
binary Byte[] GetBytes() GetSqlBinary()
bit Boolean GetBoolean() GetSqlBit()
char String

Char[]

GetString()

GetChars()

GetSqlString()
datetime DateTime GetDateTime() GetSqlDateTime()
decimal Decimal GetDecimal() GetSqlDecimal()
float Double GetDouble() GetSqlDouble()
image Byte[] GetBytes() GetSqlBinary()
int Int32 GetInt32() GetSqlInt32()
money Decimal GetDecimal() GetSqlMoney()
nchar String

Char[]

GetString()

GetChars()

GetSqlString()
ntext String

Char[]

GetString()

GetChars()

GetSqlString()
numeric Decimal GetDecimal() GetSqlDecimal()
nvarchar String

Char[]

GetString()

GetChars()

GetSqlString()
real Single GetFloat() GetSqlSingle()
smalldatetime DateTime GetDateTime() GetSqlDateTime()
smallint Int16 GetInt16() GetSqlInt16()
smallmoney Decimal GetDecimal() GetSqlDecimal()
sql_variant Object * GetValue() * GetSqlValue() *
text String

Char[]

GetString()

GetChars()

GetSqlString()
timestamp Byte[] GetBytes() GetSqlBinary()
tinyint Byte GetByte() GetSqlByte()
uniqueidentifier Guid GetGuid() GetSqlGuid()
varbinary Byte[] GetBytes() GetSqlBinary()
varchar String

Char[]

GetString()

GetChars()

GetSqlString()

* It is recommended that you use a specific typed accessor if you know the underlying type of the sql_variant.

.NET Framework Data Provider for OLE DB

ADO type OLE DB type .NET Framework type .NET Framework typed accessor
adBigInt DBTYPE_I8 Int64 GetInt64()
adBinary DBTYPE_BYTES Byte[] GetBytes()
adBoolean DBTYPE_BOOL Boolean GetBoolean()
adBSTR DBTYPE_BSTR String GetString()
adChapter DBTYPE_HCHAPTER Supported through the DataReader. See Retrieving Data Using the DataReader. GetValue()
adChar DBTYPE_STR String GetString()
adCurrency DBTYPE_CY Decimal GetDecimal()
adDate DBTYPE_DATE DateTime GetDateTime()
adDBDate DBTYPE_DBDATE DateTime GetDateTime()
adDBTime DBTYPE_DBTIME DateTime GetDateTime()
adDBTimeStamp DBTYPE_DBTIMESTAMP DateTime GetDateTime()
adDecimal DBTYPE_DECIMAL Decimal GetDecimal()
adDouble DBTYPE_R8 Double GetDouble()
adError DBTYPE_ERROR ExternalException GetValue()
adFileTime DBTYPE_FILETIME DateTime GetDateTime()
adGUID DBTYPE_GUID Guid GetGuid()
adIDispatch DBTYPE_IDISPATCH * Object GetValue()
adInteger DBTYPE_I4 Int32 GetInt32()
adIUnknown DBTYPE_IUNKNOWN * Object GetValue()
adNumeric DBTYPE_NUMERIC Decimal GetDecimal()
adPropVariant DBTYPE_PROPVARIANT Object GetValue()
adSingle DBTYPE_R4 Single GetFloat()
adSmallInt DBTYPE_I2 Int16 GetInt16()
adTinyInt DBTYPE_I1 Byte GetByte()
adUnsignedBigInt DBTYPE_UI8 UInt64 GetValue()
adUnsignedInt DBTYPE_UI4 UInt32 GetValue()
adUnsignedSmallInt DBTYPE_UI2 UInt16 GetValue()
adUnsignedTinyInt DBTYPE_UI1 Byte GetByte()
adVariant DBTYPE_VARIANT Object GetValue()
adWChar DBTYPE_WSTR String GetString()
adUserDefined DBTYPE_UDT not supported    
adVarNumeric DBTYPE_VARNUMERIC not supported    

* For OLE DB types DBTYPE_IUNKNOWN and DBTYPE_IDISPATCH, the object reference is a marshaled representation of the pointer.

.NET Framework Data Provider for ODBC

ODBC type .NET Framework type .NET Framework typed accessor
SQL_BIGINT Int64 GetInt64()
SQL_BINARY Byte[] GetBytes()
SQL_BIT Boolean GetBoolean()
SQL_CHAR String

Char[]

GetString()

GetChars()

SQL_DECIMAL Decimal GetDecimal()
SQL_DOUBLE Double GetDouble()
SQL_GUID Guid GetGuid()
SQL_INTEGER Int32 GetInt32()
SQL_LONG_VARCHAR String

Char[]

GetString()

GetChars()

SQL_LONGVARBINARY Byte[] GetBytes()
SQL_NUMERIC Decimal GetDecimal()
SQL_REAL Single GetFloat()
SQL_SMALLINT Int16 GetInt16()
SQL_TINYINT Byte GetByte()
SQL_TYPE_TIMES DateTime GetDateTime()
SQL_TYPE_TIMESTAMP DateTime GetDateTime()
SQL_VARBINARY Byte[] GetBytes()
SQL_WCHAR String

Char[]

GetString()

GetChars()

SQL_WLONGVARCHAR String

Char[]

GetString()

GetChars()

SQL_WVARCHAR String

Char[]

GetString()

GetChars()

.NET Framework Data Provider for Oracle

Oracle type .NET Framework type .NET Framework typed accessor OracleType typed accessor
BFILE Byte[] GetBytes() GetOracleBFile()
BLOB Byte[] GetBytes() GetOracleLob()
CHAR String

Char[]

GetString()

GetChars()

GetOracleString()
CLOB String

Char[]

GetString()

GetChars()

GetOracleLob()
DATE DateTime GetDateTime() GetOracleDateTime()
FLOAT Decimal GetDecimal() GetOracleNumber() **
INTEGER Decimal GetDecimal() GetOracleNumber() **
INTERVAL YEAR TO MONTH * Int32 GetInt32() GetOracleMonthSpan()
INTERVAL DAY TO SECOND * TimeSpan GetTimeSpan() GetOracleTimeSpan()
LONG String

Char[]

GetString()

GetChars()

GetOracleString()
LONG RAW Byte[] GetBytes() GetOracleBinary()
NCHAR String

Char[]

GetString()

GetChars()

GetOracleString()
NCLOB String

Char[]

GetString()

GetChars()

GetOracleLob()
NUMBER Decimal GetDecimal() GetOracleNumber() **
NVARCHAR2 String

Char[]

GetString()

GetChars()

GetOracleString()
RAW Byte[] GetBytes() GetOracleBinary()
REF CURSOR            
ROWID String

Char[]

GetString()

GetChars()

GetOracleString()
TIMESTAMP * DateTime GetDateTime() GetOracleDateTime()
TIMESTAMP WITH LOCAL TIME ZONE * DateTime GetDateTime() GetOracleDateTime()
TIMESTAMP WITH TIME ZONE * DateTime GetDateTime() GetOracleDateTime()
UNSIGNED INTEGER Decimal GetDecimal() GetOracleNumber() **
VARCHAR2 String

Char[]

GetString()

GetChars()

GetOracleString()

* The specified Oracle type is only available when using both Oracle 9i client and server software.

** An Oracle NUMBER can have a maximum of 38 significant digits. The .NET Framework decimal type is limited to 28 digits. Reading an Oracle NUMBER into a .NET Framework decimal type results in an OverflowException for NUMBER values exceeding 28 digits. If you are reading an Oracle NUMBER value from an OracleDataReader, it is recommended that you call the GetOracleNumber typed accessor method to return Oracle NUMBER values as an OracleNumber. If you are filling a DataSet, you can use the FillError event to determine if an OverflowException has occurred and take appropriate action. For information on the FillError event, see Working with DataAdapter Events.

See Also

Populating a DataSet from a DataAdapter

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