[ Team LiB ] Recipe 2.8 Mapping .NET Data Provider Data Types to .NET Framework Data Types Problem You want to convert between .NET provider data types and .NET Framework data types. Solution You need to understand the .NET Framework data types; their mappings to SQL Server, OLE DB, ODBC, and Oracle data types; and how to properly cast them. The .NET Framework typed accessors and .NET Framework provider-specific typed accessors for use with the DataReader class are also important. Discussion The ADO.NET DataSet and contained objects are data source independent. The DataAdapter is used to retrieve data into the DataSet and to reconcile modifications made to the data to the data source at some later time. The implication is that data in the DataTable objects contained in the DataSet are .NET Framework data types rather than data types specific to the underlying data source or the .NET data provider used to connect to that data source. While the DataReader object for a data source is specific to the .NET data provider used to retrieve the data, the values in the DataReader are stored in variables with .NET Framework data types. The .NET Framework data type is inferred from the .NET data provider used to fill the DataSet or build the DataReader. The DataReader has typed accessor methods that improve performance by returning a value as a specific .NET Framework data type when the data type is known, thereby eliminating the need for additional type conversion. For more information about using typed accessors with a DataReader, see Recipe 9.6 . Some DataReader classes expose data source specific accessor methods as well. For example, the SqlDataReader exposes accessor methods that return SQL Server data types as objects of System.Data.SqlType. The following example shows how to cast a value from a DataReader to a .NET Framework data type and how to use the .NET Framework typed accessor and the SQL Server-specific typed accessor: // Create the connection and the command. SqlConnection conn = new SqlConnection( ConfigurationSettings.AppSettings["Sql_ConnectString"]); SqlCommand cmd = new SqlCommand( "SELECT CategoryID, CategoryName FROM Categories", conn); // Open the connection and build the DataReader. conn.Open( ); SqlDataReader dr = cmd.ExecuteReader( ); // Get the CategoryID from the DataReader and cast to int. int categoryId = Convert.ToInt32(dr[0]); // Get the CategoryID using typed accessor. int taCategoryId = dr.GetInt32(0); // Get the CategoryID using the SQL Server-specific accessor. System.Data.SqlTypes.SqlInt32 sqlCategoryId = dr.GetSqlInt32(0); In all cases, a null value for a .NET Framework data type is represented by System.DBNull.Value. Table 2-7 lists the inferred .NET Framework data type, the .NET Framework typed accessor for the DataReader, and the SQL Server-specific typed accessor for each SQL Server data type. Table 2-7. Data types and accessors for SQL Server .NET data provider SQL Server data type .NET Framework data type .NET Framework typed accessor SQLType typed accessor bigint Int64 GetInt64( ) GetSqlInt64( ) binary Byte[] GetBytes( ) GetSqlBinary( ) bit Boolean GetBoolean( ) GetSqlBit( ) char StringChar[] 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 StringChar[] GetString( )GetChars( ) GetSqlString( ) ntext StringChar[] GetString( )GetChars( ) GetSqlString( ) numeric Decimal GetDecimal( ) GetSqlDecimal( ) nvarchar StringChar[] 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 StringChar[] GetString( )GetChars( ) GetSqlString( ) timestamp Byte[] GetBytes( ) GetSqlBinary( ) tinyint Byte GetByte( ) GetSqlByte( ) uniqueidentifier Guid GetGuid( ) GetSqlGuid( ) varbinary Byte[] GetBytes( ) GetSqlBinary( ) varchar StringChar[] GetString( )GetChars( ) GetSqlString( ) Table 2-8 lists the inferred .NET Framework data type, the .NET Framework typed accessor for the DataReader for each OLE DB type, and the corresponding ADO type. Table 2-8. Data types and accessors for OLE DB .NET data provider OLE DB data type ADO type .NET Framework data type .NET Framework typed accessor DBTYPE_BOOL adBoolean Boolean GetBoolean( ) DBTYPE_BSTR adBSTR String GetString( ) DBTYPE_BYTES adBinary Byte[] GetBytes( ) DBTYPE_CY adCurrency Decimal GetDecimal( ) DBTYPE_DATE adDate DateTime GetDateTime( ) DBTYPE_DBDATE adDBDate DateTime GetDateTime( ) DBTYPE_DBTIME adDBTime DateTime GetDateTime( ) DBTYPE_DBTIMESTAMP adDBTimeStamp DateTime GetDateTime( ) DBTYPE_DECIMAL adDecimal Decimal GetDecimal( ) DBTYPE_ERROR adError ExternalException GetValue( ) DBTYPE_FILETIME adFileTime DateTime GetDateTime( ) DBTYPE_GUID adGUID Guid GetGuid( ) DBTYPE_HCHAPTER adChapter See footnote 1 GetValue( ) DBTYPE_I1 adTinyInt Byte GetByte( ) DBTYPE_I2 adSmallInt Int16 GetInt16( ) DBTYPE_I4 adInteger Int32 GetInt32( ) DBTYPE_I8 adBigInt Int64 GetInt64( ) DBTYPE_IDISPATCH2 adIDispatch Object GetValue( ) DBTYPE_IUNKNOWN2 adIUnknown Object GetValue( ) DBTYPE_NUMERIC adNumeric Decimal GetDecimal( ) DBTYPE_PROPVARIANT adPropVariant Object GetValue( ) DBTYPE_R4 adSingle Single GetFloat( ) DBTYPE_R8 adDouble Double GetDouble( ) DBTYPE_STR adChar String GetString( ) DBTYPE_UI1 adUnsignedTinyInt Byte GetByte( ) DBTYPE_UI2 adUnsignedSmallInt UInt16 GetValue( ) DBTYPE_UI4 adUnsignedInt UInt32 GetValue( ) DBTYPE_UI8 adUnsignedBigInt UInt64 GetValue( ) DBTYPE_UDT adUserDefined Not supported Not supported DBTYPE_VARIANT adVariant Object GetValue( ) DBTYPE_VARNUMERIC adVarNumeric Not supported Not supported DBTYPE_WSTR adWChar String GetString( ) 1 Supported using the DataReader. For more information, see Recipe 2.20. 2 The object reference is a marshaled representation of the pointer. Table 2-9 lists the inferred .NET Framework data type and the .NET Framework typed accessor for the DataReader for each ODBC data type. Table 2-9. Data types and accessors for ODBC .NET data provider ODBC data type .NET Framework data type .NET Framework typed accessor SQL_BIGINT Int64 GetInt64( ) SQL_BINARY Byte[] GetBytes( ) SQL_BIT Boolean GetBoolean( ) SQL_CHAR StringChar[] GetString( )GetChars( ) SQL_DECIMAL Decimal GetDecimal( ) SQL_DOUBLE Double GetDouble( ) SQL_GUID Guid GetGuid( ) SQL_INTEGER Int32 GetInt32( ) SQL_LONG_VARCHAR StringChar[] 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 StringChar[] GetString( )GetChars( ) SQL_WLONGVARCHAR StringChar[] GetString( )GetChars( ) SQL_WVARCHAR StringChar[] GetString( )GetChars( ) Table 2-10 lists the inferred .NET Framework data type, the .NET Framework typed accessor for the DataReader, and the Oracle-specific typed accessor for each Oracle data type. Table 2-10. Data types and accessors for Oracle .NET data provider Oracle data type .NET Framework data type .NET Framework typed accessor OracleType typed accessor BFILE Byte[] GetBytes( ) GetOracleBFile( ) BLOB Byte[] GetBytes( ) GetOracleLob( ) CHAR StringChar[] GetString( )GetChars( ) GetOracleString( ) CLOB StringChar[] GetString( )GetChars( ) GetOracleLob( ) DATE DateTime GetDateTime( ) GetOracleDateTime( ) FLOAT Decimal GetDecimal( ) GetOracleNumber( )2 INTEGER Decimal GetDecimal( ) GetOracleNumber( )2 INTERVAL YEAR TO MONTH1 Int32 GetInt32( ) GetOracleMonthSpan( ) INTERVAL DAY TO SECOND1 TimeSpan GetTimeSpan( ) GetOracleTimeSpan( ) LONG StringChar[] GetString( )GetChars( ) GetOracleString( ) LONG RAW Byte[] GetBytes( ) GetOracleBinary( ) NCHAR StringChar[] GetString( )GetChars( ) GetOracleString( ) NCLOB StringChar[] GetString( )GetChars( ) GetOracleLob( ) NUMBER Decimal GetDecimal( ) GetOracleNumber( )2 NVARCHAR2 StringChar[] GetString( )GetChars( ) GetOracleString( ) RAW Byte[] GetBytes( ) GetOracleBinary( ) REF CURSOR n/a n/a n/a ROWID StringChar[] GetString( )GetChars( ) GetOracleString( ) TIMESTAMP1 DateTime GetDateTime( ) GetOracleDateTime( ) TIMESTAMP WITH LOCAL TIME ZONE1 DateTime GetDateTime( ) GetOracleDateTime( ) TIMESTAMP WITH TIME ZONE1 DateTime GetDateTime( ) GetOracleDateTime( ) UNSIGNED INTEGER Decimal GetDecimal( ) GetOracleNumber( )2 VARCHAR2 StringChar[] GetString( )GetChars( ) GetOracleString( ) 1 Available only when using both Oracle 9i client and server software. 2 The Oracle NUMBER type has a maximum of 38 significant digits while the .NET Framework decimal type has a maximum of 28. An OverflowException will be raised if the Oracle NUMBER type has more than 28 significant digits. For details about inferred .NET Framework data types, .NET Framework typed accessors for the DataReader, and provider-specific typed accessors for other .NET data providers, consult the documentation for the specific .NET data provider. [ Team LiB ] . 2.8 Mapping .NET Data Provider Data Types to .NET Framework Data Types Problem You want to convert between .NET provider data types and .NET Framework data. data types rather than data types specific to the underlying data source or the .NET data provider used to connect to that data source. While the DataReader