Accessing XML Data
There are two separate methods of retrieving XML data from a data source: one uses CStreamRowset and the other uses CXMLAccessor.
Functionality |
CStreamRowset |
CXMLAccessor |
|---|---|---|
Amount of data transferred |
Retrieves data from all columns and rows at once. |
Retrieves data from all columns but only one row at a time. You must navigate rows using methods such as MoveNext. |
Formatting the string |
SQL Server formats the XML string and sends it to the consumer. |
Retrieves rowset data in its native format (requests that the provider send it as Unicode strings) and then builds the string containing the data in XML format. |
Control over formatting |
You have some level of control over how the XML string is formatted by setting some SQL Server 2000-specific properties. |
You have no control over the format of the generated XML string. |
While CStreamRowset provides a more overall efficient way of retrieving data in XML format, it is only supported by SQL Server 2000.
Retrieving XML Data Using CStreamRowset
You specify CStreamRowset as the rowset type in your CCommand or CTable declaration. You can use it with your own accessor or no accessor, for example:
CCommand<CAccessor<CMyAccessor>, CStreamRowset> myCmd;
-or-
CCommand<CNoAccessor, CStreamRowset> myCmd;
Normally when you call CCommand::Open (specifying, for example, CRowset as the TRowset class), it obtains an IRowsetpointer. ICommand::Execute returns an IRowsetpointer, which is stored in the m_spRowset member of the CRowset object. Methods such as MoveFirst, MoveNext, and GetData use that pointer to retrieve the data.
By contrast, when you call CCommand::Open (but specify CStreamRowset as the TRowset class), ICommand::Execute returns an ISequentialStream pointer, which is stored in the m_spStream data member of CStreamRowset. You then use the Read method to retrieve the (Unicode string) data in XML format. For example:
myCmd.m_spStream->Read()
SQL Server 2000 performs the XML formatting and returns all columns and all rows of the rowset as one XML string.
For an example using the Read method, see "Adding XML Support to the Consumer" in Implementing a Simple Consumer.
Note
XML support using CStreamRowset works with SQL Server 2000 only and requires that you have the OLE DB Provider for SQL Server 2000 (installed with MDAC).
Retrieving XML Data Using CXMLAccessor
CXMLAccessor allows you to access data from a data source as string data when you have no knowledge of the data store's schema. CXMLAccessor works like CDynamicStringAccessorW except that the former converts all data accessed from the data store as XML-formatted (tagged) data. The XML tag names match the data store's column names as closely as possible.
Use CXMLAccessor as you would any other accessor class, passing it as a template parameter to CCommand or CTable:
CTable<CXMLAccessor, CRowset> rs;
Use GetXMLRowData to retrieve data from the table one row at a time, and navigate rows using methods such as MoveNext, for example:
// Open data source, session, and rowset
hr = rs.MoveFirst();
while( SUCCEEDED(hr) && hr != DB_S_ENDOFROWSET )
{
CStringW strRowData;
myCmd.GetXMLRowData(strRowData);
printf_s( "%S\n", strRowData );
hr = rs.MoveNext();
}
You can use GetXMLColumnData to retrieve the column (data type) information as XML-formatted string data.