DATAJPA-1379 - Fixed detection of PersistenceProvider when EntityManager is a proxy.

We now use the delegate to test the applicability of the PersistenceProvider not just for determining the and the key cash.

This fixes the issue because the underlying issue was that the generic PersistenceProvider was used.
Which return false for `canExtractQuery` which prevented the constructor call in the query to be detected.

Original pull request: #287.

src/main/java/org/springframework/data/jpa/provider/JpaClassUtils.java

@@ -43,7 +43,11 @@ abstract class JpaClassUtils {
 	 * @return
 	 */
 	public static boolean isEntityManagerOfType(EntityManager em, String type) {
-		return isOfType(em, type, em.getDelegate().getClass().getClassLoader());
+		Object delegate = em.getDelegate();
+		if (delegate instanceof EntityManager) {
+			em = (EntityManager) delegate;
+		}
+		return isOfType(em, type, delegate.getClass().getClassLoader());
 	}
 
 	public static boolean isMetamodelOfType(Metamodel metamodel, String type) {

src/main/java/org/springframework/data/jpa/provider/PersistenceProvider.java

@@ -44,6 +44,7 @@ import org.springframework.util.ConcurrentReferenceHashMap;
  * @author Oliver Gierke
  * @author Thomas Darimont
  * @author Mark Paluch
+ * @author Jens Schauder
  */
 public enum PersistenceProvider implements QueryExtractor, ProxyIdAccessor {
 
@@ -224,7 +225,7 @@ public enum PersistenceProvider implements QueryExtractor, ProxyIdAccessor {
 		String OPENJPA_JPA_METAMODEL_TYPE = "org.apache.openjpa.persistence.meta.MetamodelImpl";
 	}
 
-	private static ConcurrentReferenceHashMap<Class<?>, PersistenceProvider> CACHE = new ConcurrentReferenceHashMap<Class<?>, PersistenceProvider>();
+	static ConcurrentReferenceHashMap<Class<?>, PersistenceProvider> CACHE = new ConcurrentReferenceHashMap<Class<?>, PersistenceProvider>();
 
 	private final Iterable<String> entityManagerClassNames;
 	private final Iterable<String> metamodelClassNames;

src/test/java/org/springframework/data/jpa/provider/PersistenceProviderUnitTests.java

@@ -40,6 +40,7 @@ import org.springframework.util.ClassUtils;
  *
  * @author Thomas Darimont
  * @author Oliver Gierke
+ * @author Jens Schauder
  */
 public class PersistenceProviderUnitTests {
 
@@ -47,6 +48,9 @@ public class PersistenceProviderUnitTests {
 
 	@Before
 	public void setup() {
+
+		PersistenceProvider.CACHE.clear();
+
 		this.shadowingClassLoader = new ShadowingClassLoader(getClass().getClassLoader());
 	}
 
@@ -80,12 +84,25 @@ public class PersistenceProviderUnitTests {
 		assertThat(fromEntityManager(em), is(HIBERNATE));
 	}
 
+	@Test // DATAJPA-1379
+	public void detectsProviderFromProxiedEntityManager() throws Exception {
+
+		shadowingClassLoader.excludePackage("org.eclipse.persistence.jpa");
+
+		EntityManager em = mockProviderSpecificEntityManagerInterface(ECLIPSELINK_ENTITY_MANAGER_INTERFACE);
+
+		EntityManager emProxy = Mockito.mock(EntityManager.class);
+		Mockito.when(emProxy.getDelegate()).thenReturn(em);
+
+		assertThat(fromEntityManager(emProxy), is(ECLIPSELINK));
+	}
+
 	private EntityManager mockProviderSpecificEntityManagerInterface(String interfaceName) throws ClassNotFoundException {
 
 		Class<?> providerSpecificEntityManagerInterface = InterfaceGenerator.generate(interfaceName, shadowingClassLoader,
 				EntityManager.class);
 
-		EntityManager em = EntityManager.class.cast(Mockito.mock(providerSpecificEntityManagerInterface));
+		EntityManager em = (EntityManager) Mockito.mock(providerSpecificEntityManagerInterface);
 		Mockito.when(em.getDelegate()).thenReturn(em); // delegate is used to determine the classloader of the provider
 																										// specific interface, therefore we return the proxied
 																										// EntityManager.