Getting Startedwith pureQuery

Chapter 15 – pureQuery and pureXML 289
expression will be used to update the correct nodes in the original XML document. Listing
15.2 shows an example of an XQuery Transform expression that can be used to update
the Employee information in the database:
public static void updateEmployee(Data data, Employee emp){
String sql = "update employee set doc = xmlquery(" +
"'copy $new := $DOC " +
"modify (do replace value of $new/employee/name/first with
$firstname," +
"do replace value of $new/employee/name/last with $lastname," +
"do replace value of $new/employee/office with $office)" +
"return $new' " +
"passing cast(:firstname as varchar(20)) as \"firstname\", " +
"cast(:lastname as varchar(20)) as \"lastname\"," +
"cast(:office as INTEGER) as \"office\"" +
") where id = :id";
data.update(sql, emp);
}
Listing 15.2 – Using an XQuery Transform expression
Using this approach allows the application developers to be oblivious of schema evolution
in the application data, as the mapping is done in the database, hiding these changes from
the application.
15.3 Give control to the data access API
In this approach, we will show how XML data can be mapped into Java objects and viceversa
using the data access API, instead of doing this mapping at the database level like in
the previous approach.
The pureQuery API provides several plug-in mechanisms, including custom result set and
custom data row handlers. These custom handlers provide you with means to override
default mapping strategies from relational data into Java beans. The ResultHandler lets
you control the mapping strategy for the entire result set. This is very useful for aggregation
queries and one-to-many relationships, when several consecutive result sets may contain
information about the same business object. The RowHandler lets you define how
individual relational result set rows are mapped into a Java bean. Unlike the ResultHandler,
the RowHandler only has access to the current row in the result set and not the entire
result set.
By taking advantage of these plug-in mechanisms, you can use one of the several existing
Java-XML mapping frameworks to map from XML documents stored as pureXML data into
your business logic Java beans, as shown in Figure 15.2.