Getting Startedwith pureQuery

Chapter 9 – Persistence Frameworks and Data Access: Context for pureQuery 177
See Chapter 13 for more information about implementing custom handlers.
9.3.3 Query over Collections with pureQuery
pureQuery supports transparent, mixed, in-memory vs. relational queries using standard
SQL. This feature is called Query over Collections, and allows the object-relational layer to
be implemented using a hybrid approach dividing query processing between a traditional
relational database backend and in-memory objects.
Depending on the kind of processing that is required, there may be systems which can be
optimized by pulling a large, initial collection of data from the database using a traditional
database query, then closing the database connection and performing several further,
filtering queries on the initial collection in-memory. The advantage of this scheme is that
the initial database connection resources can be freed up for other clients. Likewise, if the
same set of initial data will have a number of filtering queries performed on it, the ability to
query over the initial collection in-memory cuts the cost of additional trips to the database
for each subsequent sub-query.
To query over collections, pureQuery accepts a parameter marker in the place of the table
name in any SQL query using SQL-92 standard syntax. The application then provides a
java collection for the table parameter to the annotated or inline pureQuery method which
performs the query.
In Listing 3.4, a java List containing the contents of a previous database query is provided
as a parameter to a pureQuery query-over-collection annotated method. In this example,
the pureQuery numbered parameter marker (“?1”) represents a table in the SQL query
syntax. pureQuery’s implementation for this method will treat the List of Customers as the
table over which to perform the query.
import com.company.Customer;
import com.company.Campaign.CitySize;
public interface RegionReport
{
@Select(sql="SELECT COUNT(DISTINCT city) FROM ?1")
public Integer countCities (List curRegion);
}
Listing 9.4 - An example of a Query Over Collection, in this case a List of Customers.
9.3.4 XML entity mapping with pureQuery
One common way to increase the flexibility of the object-relational mapping layer is to
separate the object-relational mapping definition from the application code. pureQuery
supports XML entity-mapping files for annotated methods defined for pureQuery data
access objects. See Chapter 11 to learn how to create pureQuery data access objects with
user-defined, annotated methods using a pureQuery development project. To use XML
entity mapping with pureQuery, an XML object-relational mapping file is provided to the
pureQuery tooling along with the pureQuery annotated interface used to generate the class