EntityManager

From CauchoWiki

[edit] API

   public interface EntityManager {
   public <T> T find(Class<T> entityClass, Object key);
   public <T> T getReference(Class<T> entityClass, Object key);
   public void refrech(Object entity);
   
   public void persist(Object entity);
   public <T> T merge(T entity);
   public void remove(Object entity);

   public Query createQuery(String sql);
   public Query createNamedQuery(String name);
   public Query createNativeQuery(String sql, Class resultClass);
   public Query createNativeQuery(String sql, String resultSetMapping);

   public boolean contains(Object entity);
   public void clear();
   public void flush();
   public boolean isOpen();
   public void close();

   public void setFlushMode(FlushModeType flushMode);   
   public FlushModeType getFlushMode();

   public void lock(Object entity, LockModeType lockMode);   
   
   public EntityTransaction getTransaction();
   }

[edit] @PersistenceContext injection

The EntityManager for a persistence unit can be assigned using EJB injection with the @PersistenceContext annotation.

The @PersistenceContext EntityManager is a proxy ThreadLocal. In other words, the underlying EntityManager is specific to the request thread and is thread-safe. Different request threads for the same @PersistenceContext proxy will be using different underlying EntityManagers.

The configuration for a servlet might look like:

   public class MyServlet extends GenericServlet {
 
       @PersistenceContext
       EntityManager _em;

       public void service(ServletRequest req, ServletResponse res)
       {
           TestBean test = _em.find(TestBean.class, new Integer(1));
           ...
       }
   }

@PersistenceContext(unitName="xxx") can be used if the environment has more than one persistence unit.

@PersistenceContext can be used for session beans, message-driver beans, servlets, filters, and JSP pages.

[edit] Obtaining an EntityManager using JNDI

In Amber, the EntityManager for a persistence unit is stored as "java:comp/env/persistence/PersistenceContext/xxx", where "xxx" is the name of the persistence unit.

(The CMP 2.1 implementation uses a name of "resin-ejb".)