7.5.3. Data Types
Data Type Mappings in Rowsets and Parameters
The methods that provide information about rowset columns and command parameters (IColumnsInfo::GetColumnInfo, ICommandWithParameters::GetParameterInfo) use the mapping of Virtuoso data types into OLE DB data types shown in the following table.
Table 7.18. Data Type Mappings
| Virtuoso Type | OLE DB Type |
|---|---|
| CHAR | DBTYPE_STR |
| VARCHAR | DBTYPE_STR |
| LONG VARCHAR | DBTYPE_STR |
| NCHAR | DBTYPE_WSTR |
| NVARCHAR | DBTYPE_WSTR |
| LONG NVARCHAR | DBTYPE_WSTR |
| NUMERIC | DBTYPE_NUMERIC |
| DECIMAL | DBTYPE_NUMERIC |
| SMALLINT | DBTYPE_I2 |
| INTEGER | DBTYPE_I4 |
| FLOAT | DBTYPE_R8 |
| DOUBLE | DBTYPE_R8 |
| REAL | DBTYPE_R4 |
| VARBINARY | DBTYPE_BYTES |
| LONG VARBINARY | DBTYPE_BYTES |
| DATE | DBTYPE_DBDATE |
| TIME | DBTYPE_DBTIME |
| DATETIME | DBTYPE_DBTIMESTAMP |
| TIMESTAMP | BINARY |
Data Type Conversions
Applications can bind column and parameter values using data types different from those described in the section called “Data Type Mappings in Rowsets and Parameters” . In such cases VIRTOLEDB uses OLE DB Data Conversion Library. See MDAC documentation for the list of supported data type conversions.
Long Data Types
Long data types include LONG VARCHAR, LONG NVARCHAR, and LONG VARBINARY. A long value can only be bound to a buffer that have one of these OLE DB types:
-
DBTYPE_IUNKNOWN
-
DBTYPE_STR
-
DBTYPE_STR | DBTYPE_BYREF
-
DBTYPE_WSTR
-
DBTYPE_WSTR | DBTYPE_BYREF
-
DBTYPE_BYTES
-
DBTYPE_BYTES | DBTYPE_BYREF
Other type conversions are not supported.
If a long data is bound to a DBTYPE_IUNKNOWN type, this implies the use of the ISequentialStream interface. VIRTOLEDB supports the ISequentialStream::Read method both when getting and setting data. The ISequentialStream::Write method is never supported.