Introdução ao OData com o Olingo

@Entity
@Table(name="car_maker")
public class CarMaker {
    @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
    private Long id;
    @NotNull
    private String name;
    @OneToMany(mappedBy="maker",orphanRemoval = true,cascade=CascadeType.ALL)
    private List models;
    // ... getters, setters and hashcode omitted
}

@Entity
@Table(name="car_model")
public class CarModel {
    @Id @GeneratedValue(strategy=GenerationType.AUTO)
    private Long id;

    @NotNull
    private String name;

    @NotNull
    private Integer year;

    @NotNull
    private String sku;

    @ManyToOne(optional=false,fetch=FetchType.LAZY) @JoinColumn(name="maker_fk")
    private CarMaker maker;

    // ... getters, setters and hashcode omitted
}

@Component
public class CarsODataJPAServiceFactory extends ODataJPAServiceFactory {
    // other methods omitted...

    @Override
    public ODataJPAContext initializeODataJPAContext() throws ODataJPARuntimeException {
        ODataJPAContext ctx = getODataJPAContext();
        ODataContext octx = ctx.getODataContext();
        HttpServletRequest request = (HttpServletRequest) octx.getParameter(
          ODataContext.HTTP_SERVLET_REQUEST_OBJECT);
        EntityManager em = (EntityManager) request
          .getAttribute(EntityManagerFilter.EM_REQUEST_ATTRIBUTE);

        ctx.setEntityManager(em);
        ctx.setPersistenceUnitName("default");
        ctx.setContainerManaged(true);
        return ctx;
    }
}

@Component
@ApplicationPath("/odata")
public class JerseyConfig extends ResourceConfig {
    public JerseyConfig(CarsODataJPAServiceFactory serviceFactory, EntityManagerFactory emf) {
        ODataApplication app = new ODataApplication();
        app
          .getClasses()
          .forEach( c -> {
              if ( !ODataRootLocator.class.isAssignableFrom(c)) {
                  register(c);
              }
          });

        register(new CarsRootLocator(serviceFactory));
        register(new EntityManagerFilter(emf));
    }

    // ... other methods omitted
}

@Path("/")
public class CarsRootLocator extends ODataRootLocator {
    private CarsODataJPAServiceFactory serviceFactory;
    public CarsRootLocator(CarsODataJPAServiceFactory serviceFactory) {
        this.serviceFactory = serviceFactory;
    }

    @Override
    public ODataServiceFactory getServiceFactory() {
       return this.serviceFactory;
    }
}

@Provider
public static class EntityManagerFilter implements ContainerRequestFilter,
  ContainerResponseFilter {

    public static final String EM_REQUEST_ATTRIBUTE =
      EntityManagerFilter.class.getName() + "_ENTITY_MANAGER";
    private final EntityManagerFactory emf;

    @Context
    private HttpServletRequest httpRequest;

    public EntityManagerFilter(EntityManagerFactory emf) {
        this.emf = emf;
    }

    @Override
    public void filter(ContainerRequestContext ctx) throws IOException {
        EntityManager em = this.emf.createEntityManager();
        httpRequest.setAttribute(EM_REQUEST_ATTRIBUTE, em);
        if (!"GET".equalsIgnoreCase(ctx.getMethod())) {
            em.getTransaction().begin();
        }
    }

    @Override
    public void filter(ContainerRequestContext requestContext,
      ContainerResponseContext responseContext) throws IOException {
        EntityManager em = (EntityManager) httpRequest.getAttribute(EM_REQUEST_ATTRIBUTE);
        if (!"GET".equalsIgnoreCase(requestContext.getMethod())) {
            EntityTransaction t = em.getTransaction();
            if (t.isActive() && !t.getRollbackOnly()) {
                t.commit();
            }
        }

        em.close();
    }
}

curl http://localhost:8080/odata/$metadata

curl http://localhost:8080/odata/CarMakers
curl http://localhost:8080/odata/CarModels
curl http://localhost:8080/odata/CarMakers(1)
curl http://localhost:8080/odata/CarModels(1)
curl http://localhost:8080/odata/CarModels(1)/CarMakerDetails

curl http://localhost:8080/odata/CarMakers?$filter=startswith(Name,'B')