I apologize in advance for a lengthy post but I guess I need to support my query with code. I am coding for a system which has 12 database instances. All databases have the same number and name of tables but the data is different (of course). Depending on a URL parameter passed from an external application, I need to choose one of the 12 databases at runtime.
I have coded a EntityFactory wrapper which takes in the URL parameter and returns an appropriate EntityManager instance using Reflection.
Problem is that the returned EntityManager, when used in find, is not loading the Entity attributes as it should. Not surprisingly, find works inside the EntityFactory wrapper.
Code:
public class ApplicationSpecificEntityManagerFactoryImpl implements
ApplicationSpecificEntityManagerFactory {
@Override
public EntityManager getEntityManager(String persistenceUnitname) {
Field[] declaredFields = getClass().getDeclaredFields();
PersistenceContext annotation = null;
for (Field field : declaredFields) {
if (field.getType() == EntityManager.class) {
annotation = field.getAnnotation(PersistenceContext.class);
if (annotation != null
&& persistenceUnitname.equals(annotation.unitName())) {
try {
EntityManagerFactory emf = Persistence
.createEntityManagerFactory(persistenceUnitname); // I don't do this in a Container, rely on DI
EntityManager em = null;
ApplicationParameter applicationParameter = null;
ApplicationParameterId id = new ApplicationParameterId(
"GCO", (short) 4, "LDAP", (short) 1);
field.set(this, emf.createEntityManager());
// em = emf.createEntityManager();
applicationParameter = ((EntityManager) field.get(this)).find(
ApplicationParameter.class, id);
System.out.println("value in ApplicationSpecificEntityManagerFactoryImpl: " + applicationParameter.getParamValue()); // prints LDAP
return (EntityManager) field.get(this);
// return em;
} catch (IllegalArgumentException ex) {
ex.printStackTrace();
} catch (IllegalAccessException ex) {
ex.printStackTrace();
}
}
} else {
continue;
}
}
return null;
}
@PersistenceContext(unitName = "myPU")
private EntityManager myEm;
@PersistenceContext(unitName = "hisPU")
private EntityManager hisEm;
}
Main class:
Code:
public class JpaTest {
public static void main(String[] args) {
ApplicationSpecificEntityManagerFactory entityManagerFactory = new ApplicationSpecificEntityManagerFactoryImpl();
ApplicationParameterManager applicationParameterManager = new JpaApplicationParameterManagerImpl(
entityManagerFactory);
applicationParameterManager.setPlantCode("myPlant");
String value = applicationParameterManager
.getApplicationParameterValue(ApplicationConstants.AUTHENTICATION_PARAMETER);
System.out.println("value in JpaTest: " + value); // prints null
}
}
Persistence.xml snippet:
Code:
<persistence-unit name="myPU" transaction-type="RESOURCE_LOCAL">
<provider>org.hibernate.ejb.HibernatePersistence</provider>
<class>com.x.y.dashboard.persistence.ApplicationParameter</class>
<class>com.x.y.dashboard.persistence.ApplicationParameterId</class>
<properties>
<property name="hibernate.hbm2ddl.auto" value="validate" />
<property name="hibernate.show_sql" value="false" />
<property name="hibernate.dialect" value="org.hibernate.dialect.MySQLDialect" />
<property name="transaction.manager_lookup_class" value="org.hibernate.transaction.JBossTransactionManagerLookup"/>
<property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost:3306/test"/>
<property name="javax.persistence.jdbc.user" value="appadmin"/>
<property name="javax.persistence.jdbc.password" value="xxx"/>
<property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver"/>
</properties>
</persistence-unit>
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