Handling Collection Query Results

TopLink provides a useCollectionClass method to all subclasses of DataReadQuery and ReadAllQuery, that you can use to configure a query to return results as any concrete instance of Collection or Map.

Do not confuse collection query result configuration with a mapping container policy (see "Configuring Container Policy"): there is no relationship between the two. Collection query result configuration determines how TopLink returns multiobject results from a particular query. A mapping container policy tells TopLink how your domain object implements a data member that contains a collection.

For example, consider a class Employee with a data member phoneNumbers. In your implementation of Employee, the getPhoneNumbers method returns a Vector. Using TopLink Workbench, you map the phoneNumbers data member as a one-to-many mapping. You configure the mapping container policy so that the mapping contains its value (many PhoneNumber objects) in a Vector. This corresponds to your implementation of Employee.

You define a ReadAllQuery named localPhoneNumbers on the DescriptorQueryManager of the PhoneNumber. The localPhoneNumbers query takes one argument, the ID of an Employee object, and returns all the phone numbers from its phoneNumbers data member whose area code is 613.

You get this query by name from the DescriptorQueryManager for PhoneNumber. You call the useCollectionClass method on this ReadAllQuery, passing in the ArrayList class. You execute the query, passing in the ID of an Employee. The query returns all the PhoneNumber objects from the Employee object's phoneNumbers data member whose area code is 613. The query returns these results as an ArrayList.