Toplink JPA and Java type mapping

Question

Hi there,
I'm struggling wit mapping an existing database using Toplink Essentials.
Specifically: I have an INT SQL field which I want to map as boolean/Boolean in my entity class.
How to do this? Either in standard JPA or with some Toplink extensions?
Markus

Answer 1

Hi Markus,
The JPA spec doesn't cover conversion/transformation but you can do it with TopLink Essentials using a Converter. I have an example pasted below that uses a converter to map between a database VARCHAR value and a pre-Java 5 enum (i.e., a hand coded enum-type class that runs in Java 1.4).
I use a descriptor customizer to get hold of the Basic mapping (in TopLink a "DirectToFieldMapping") and then plug in a converter.
--Shaun
Persistence.xml:
<property
   name="toplink.descriptor.customizer.TypeWriter"
   value="oracle.toplink.essentials.emf.examples.library.orm.TypeWriterCustomizer"/>The customizer:
public class TypeWriterCustomizer implements DescriptorCustomizer {
      * Add customizer to translate between Enum and value.
     public void customize(ClassDescriptor descriptor) throws Exception {
          DirectToFieldMapping typeMapping = (DirectToFieldMapping) descriptor.getMappingForAttributeName("type");
          Converter typeWriterEnumConverter = TypeWriterEnumConverter.getInstance();
          typeMapping.setConverter(typeWriterEnumConverter);
}The actual converter class:
* TypeWriterEnumConverter is a singleton since it has no state.
public class TypeWriterEnumConverter implements Converter {
     protected static TypeWriterEnumConverter instance = new TypeWriterEnumConverter();
     private TypeWriterEnumConverter() {}
     public static TypeWriterEnumConverter getInstance() {
          return instance;
     public Object convertDataValueToObjectValue(Object data, Session session) {
          String typeName = (String)data;
          return TWriterType.get(typeName);
     public Object convertObjectValueToDataValue(Object object, Session session) {
          TWriterType type = (TWriterType) object;
          if (type != null) {
               return type.getName();
          } else {
               return null;
     public void initialize(DatabaseMapping arg0, Session arg1) {}
     public boolean isMutable() {
          return false;
}