Applied XML Programming for Microsoft .NET.pdf - Csbdu.in

schema information to associate the element with a record in a table. The record isactually written when the end tag for that element is found. This algorithm ensures thatin the case of parent-child relationships, all the children are processed before theparent row.Transacted LoadingUnlike the T-SQL BULK INSERT statement, XML bulk loading is a sort of add-on.Because XML bulk loading is not natively part of SQL Server 2000, it never runs withinan implicit transaction, as normally happens with T-SQL statements. As a result, youmust manage transactions yourself. On the other hand, bulk loading is the kind ofoperation that sometimes does need to run in a transacted context.It goes without saying that if you can afford to run bulk loading without transactions,doing so would be greatly beneficial to the overall performance of the application.Nontransacted loading makes a lot of sense when you have to fill up empty databases.In a transactionless scenario, you lose the ability to roll back changes, but becauseyour databases were originally empty, if something goes wrong, you can clear thedatabase and start over.NoteIn nontransacted mode, XML bulk loading takes advantage of themethods of the OLE DB IRowsetFastLoad interface to do the job.Not all OLE DB providers supply the IRowsetFastLoad interface, butthe SQLOLEDB provider does.When XML bulk loading works in transacted mode, the component creates a temporaryfile for each table involved in the operation. The files will gather all the changes for thetables. When a commit occurs, the contents of the various files are flushed into thecorresponding SQL Server table using the BULK INSERT statement.XML Bulk Loading in ActionLet's see how XML bulk loading really works. As mentioned, XML bulk loading isimplemented through a COM object whose progID attribute is SQLXMLBulkLoad. Thefollowing Visual Basic 6.0 code shows how to use the object:conn = "PROVIDER=sqloledb;SERVER=localhost;" & _"database=Northwind;UID=sa"Set bulk = CreateObject("SQLXMLBulkLoad.SQLXMLBulkload.3.0")bulk.ConnectionString = connbulk.Execute "schema.xml", "data.xml"To perform bulk loading, you set the connection string and then call the Executemethod. The method takes two arguments: the schema and the XML source data. Inlineschemas are ignored, as are schema files referenced in the source file. As a result,you must always supply schema information and data through distinct XML files.Finally, note that XML documents are checked for well-formedness, but their contentsare never validated against any schema. Any contents outside the root node of thedocument—the node—are simply discarded.The following listing shows a typical source for a bulk loading operation. It adds acouple of employees, each with a few related territories.308