static access to entity manager in spring and unusual architecture

Question

quick question:

I have webapplication (wicket+spring+jpa) and was thinking about rather unusual architecture design. Please check it out and give your comments.

Answer 1

You should have a look at Spring Roo. They have something simular (no DAOs or Services), but there EntityManager is not static.

They do the trick with the @Configurable annotation in Entities:

@Entiy
@Configurable
class MyEntity() {

  @PersistenceContext
  transient EntityManager Car.entityManager;

  ...

  public static MyEntity findMyEntityById(Long id) {
    if (id == null) return null;
    return entityManager().find(MyEntity.class, id);
  }

  public static EntityManager entityManager() {
    EntityManager em = new MyEntity().entityManager;
    if (em == null) throw new IllegalStateException("Entity manager has not been injected (is the Spring Aspects JAR configured as an AJC/AJDT aspects library?)");
    return em;
  }    
}

Anyway it has two or three drawbacks:

• you need AspectJ
• this line EntityManager em = new MyEntity().entityManager; is very ugly
• testing becomes a bit difficult if you want to mock the persistent "layer". But fortunally the Spring provides a special AOP Interceptor (@see JavaDoc of org.springframework.mock.staticmock.AnnotationDrivenStaticEntityMockingControl)

But it has also some nice effects: for example the persist and delete methods become very natural, they are just member of the entity:

@Transactional
public void persist() {
    if (this.entityManager == null) this.entityManager = entityManager();
    this.entityManager.persist(this);
}

---

To make a none Roo project aviable for @Configurable you need to at LEAST doing this:

extend the pom.xml:

    3.0.5.RELEASE
    1.6.11
    1.2
    2.3.2
    UTF-8


    ...

    
        org.aspectj
        aspectjrt
        ${aspectj.version}
    
    
        org.aspectj
        aspectjweaver
        ${aspectj.version}
    
    
        org.springframework
        spring-aop
        ${spring.version}
    
    
        org.springframework
        spring-aspects
        ${spring.version}
    

...

        
            org.codehaus.mojo
            aspectj-maven-plugin
            ${aspectj-maven-plugin.version}
            
            
                
                    org.aspectj
                    aspectjrt
                    ${aspectj.version}
                
                
                    org.aspectj
                    aspectjtools
                    ${aspectj.version}
                
    
            
            
                
                    
                        compile
                        test-compile
                    
                
            
            
                true
                
                    
                        org.springframework
                        spring-aspects
                    
                    
                
                1.6
                1.6
                utf-8
            
        

Spring config: