Accessing JPA metadata

Question

I have some "none" JPA data columns that I support using @Transient methods that use JDBC to lazy fetch the data. In this case it is JGeometry, while I'm waiting for some bug fixes in the extensions Doug Clarke is working on; but the problem will extend to any data type not supported by Toplink.
To facilitate this I need to, regretfully, resort to native (SQL) queries. This requires me to know the table name associated with an entity class. My table names are overloaded using the orm.xml file, so even if I reflect on the class looking for the @Table annotation, I won't get the correct table.
My entity classes are layered into base classes that contain common attributes extended by implementing classes that add in the additional columns used for a particular client schema. The orm.xml file is used to adjust table and column names to fit a particular legacy database.
Perhaps I'm missing something, but I can't seem to find an API class in the persistence architecture that will let me discover the table name for a class or a column name for a property; useful information when I have to resort to building an SQL query.
Thanks, Mark.

Answer 1

Hi Mark,
All the meta data, including table name(s) for a class as well as the columns associated with properties are available at runtime. The code below will print out all the tables for each entity and the columns for each mapping.
EntityManagerFactory emf = Persistence.createEntityManagerFactory("demo");
EntityManager em = emf.createEntityManager();
EntityManagerImpl emImpl = (EntityManagerImpl)em;
Collection<ClassDescriptor> descs =emImpl.getServerSession().getProject().getDescriptors().values();
for (ClassDescriptor desc : descs) {
     System.out.println(desc.getTableNames());
     Collection<DatabaseMapping> mappings = desc.getMappings();
     for (DatabaseMapping databaseMapping : mappings) {
          System.out.println(databaseMapping.getField());
}If you need to do some custom coding per descriptor you can write a descriptor customizer (some links in this Cache in multiple server enviroment). In there you can use the native TopLink API above to get at the metadata for the class.
--Shaun