How to inject dynamic EntityManager into a Third Party Library - jpa

Question

I have a library with some functionality that I want to reuse in other projects. My issue is that my service requires writing to the database. I would like for my library to use the datasource of the project that is inject my service.
Here is the minimal setup of my service
#Stateless
public class CustomService {
//to be added in producer
private EntityManager em;
private Principal principal;
//default constructor
public CustomService() {}
//custom constructor called in provider
public CustomService(Principal p, EntityManager e) {
principal = p;
em = e;
}
#TransactionAttribute(TransactionAttributeType.REQUIRES_NEW)
#Transactional
public CustomJPAObject createObject(...params...) {
//create JPA Object
em.persist(customObject);
em.flush();
return customObject;
}
}
I created a Custom Annotation for overriding the datasource
#Qualifier
#Retention(RetentionPolicy.RUNTIME)
#Target({ElementType.TYPE,ElementType.FIELD, ElementType.METHOD})
public #interface DynamicDS {
#Nonbinding String value() default "";
}
I also created a Singleton to be an EntityManager Producer
#Singleton
public class CustomEMProducer {
private Map<String, EntityManagerFactory> emfMap = new HashMap<>();
#Produces #Dependent #DynamicDS
public EntityManager produceEntityManager(InjectionPoint injectionPoint) {
String dataSourceName = null;
for(Annotation qualifier: injectionPoint.getQualifiers()) {
if(qualifier instanceof DynamicDS) {
DynamicDS dds = (DynamicDS) qualifier;
dataSourceName = dds.value();
break;
}
}
EntityManagerFactory emf = emfMap.get(dataSourceName);
if (emf == null) {
emf = Persistence.createEntityManagerFactory(dataSourceName);
emfMap.put(dataSourceName, emf);
}
return emf.createEntityManager();
}
#PostConstruct
public void cleanup() {
emfMap.entrySet().stream().forEach(entry -> entry.getValue().close());
}
}
Here is the code for my Service Producer
#Stateless
public class CustomServiceProvider {
#Inject private Principal principal;
#Produces #Dependent #DynamicDS
public BackgroundJobService getBackgroundJobService(InjectionPoint injectionPoint) throws EntityManagerNotCreatedException {
Annotation dsAnnotation = null;
for(Annotation qualifier: injectionPoint.getQualifiers()) {
if(qualifier instanceof BackgroundJobDS) {
dsAnnotation = qualifier;
break;
}
}
if (dsAnnotation != null) {
EntityManager em = CDI.current().select(EntityManager.class, dsAnnotation).get();
CustomService service = new CustomService(principal, em);
return service;
}
throw new EntityManagerNotCreatedException("Could not Produce CustomService");
}
}
The following is where I try to inject my new service
#Stateless
public class ProjectService {
#Inject #DynamicDS("project-ds") CustomerService service;
public CustomObject create(...params...) {
return service.createObject(...params...);
}
}
When I deploy my code and attempt to call the injected service I get the following error:
Caused by: javax.persistence.TransactionRequiredException: no transaction is in progress
at org.hibernate.jpa.spi.AbstractEntityManagerImpl.checkTransactionNeeded(AbstractEntityManagerImpl.java:1171)
at org.hibernate.jpa.spi.AbstractEntityManagerImpl.flush(AbstractEntityManagerImpl.java:1332)
...
It looks like all of the different levels of providers are preventing the #Transactional on the CustomService.createObject() method call from propagating the transaction. Does anyone have insight into why this is or an alternate way of accomplishing my goal of injecting a dynamic EntityManager?

Answer 1

After much experimenting, I was unable to get dynamically generate an EntityManager through the above code. After much research, I gave up on trying to pass in the name from outside the 3rd part library. I would up creating the following interface:
public interface CustomEntityManager {
EntityManager getEntityManager();
}
This meant that inside the project that uses the 3rd party service I can do the create the following implementation to inject the EntityManager
public ProjectSpecificEntityManager implements CustomEntityManager {
#PersistenceContext(unitname = "project-ds")
private EntityManager em;
public EntityManager getEntityManager() {
return em;
}
}
I had to update my CustomService to the following
#Stateless
public class CustomService {
//Ignore warning about no bean eligible because it is intended
//that the project that uses this library will provide the
//implementation
#SuppressWarnings("cdi-ambiguous-dependency")
#Inject
CustomEntityManager cem;
#TransactionAttribute(TransactionAttributeType.REQUIRES_NEW)
#Transactional
public CustomJPAObject createObject(...params...) {
//create JPA Object
cem.getEntityManager().persist(customObject);
return customObject;
}
}