Re: RequestFactory - EntityManager and Server Side Question

On Tuesday, February 5, 2013 8:48:35 AM UTC+1, Manuel wrote:

Hey,

I had a look and used this to implement a servlet-module: http://code.google.com/p/google-guice/wiki/ServletModule
My Module looks like the example from your session per request link: http://code.google.com/p/google-guice/wiki/JPA#Web_Environments_%28session-per-http-request%29

In the web.xml I put a Listener.
<listener>
  <listener-class>de.mash.project.shared.MyGuiceServletConfig</listener-class>
</listener>

The Listener looks like this:
public class MyGuiceServletConfig extends GuiceServletContextListener {

      @Override
      protected Injector getInjector() {
          return Guice.createInjector(new MyServletModule());         
      } 
    }

Then I added the following in my Worker Entity-class:

//@RequestScoped

@Entity
@Table(name = "Worker")
public class Worker {

@Transient
@Inject    static EntityManager em3;

You don't want a single EntityManager for the whole app lifetime and shared between threads, so you have to use a Provider<EntityManager> here.

 

...

 @Transactional
  public void persist() {...}


@Transactional
public static Worker findWorker(Long id) {...}
}

I don't think Guice can intercept static methods, so you'd have to explicitly begin/end a transaction here.

 

I set a breakpoint on my doFilter() method in my PersistFilter, and its just doing what Jens descripted above.

EntityManager em = create(); //save this em instance somewhere so you can access it in your RF service methods, e.g. using a static ThreadLocal

filterChain.doFilter() //this calls the RF servlet and does all the RF requests

em.close() //Don't forget to cleanup the ThreadLocal if you have used one.

Instead of EntityManager, its called UnitOfWork

I thought my WorkerEntity´s em3 EntityManager would now get injected but it doesnt :(

Static injection needs to be requested explicitly from your module: https://code.google.com/p/google-guice/wiki/Injections#Static_Injections

 

Im not sure if I´m totally wrong, or if just something small is missing/wrong.

Use a service (with a custom ServiceLocator that uses Guice, see https://github.com/tbroyer/gwt-maven-archetypes/tree/master/guice-rf-activities/src/main/resources/archetype-resources/__rootArtifactId__-server/src/main/java for an example) instead of static methods in your entity; that way you'll remove the need for static injection and @Transaction will Just Work™.

Beware that your service will be a "quasi-singleton" in RequestFactory (singleton that can be garbage-collected under low-memory conditions and recreated later when needed), so always inject Provider<>s.

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