Use IdentifiableType.hasSingleIdAttribute() to detect IdClass presence to obtain IdClass attributes.

We now use IdentifiableType.hasSingleIdAttribute() to detect whether a type should have an IdClass. hasSingleIdAttribute is defined to return false if an IdClass is being used. It could also return false in case multiple identifier attributes are in place (composite Id) which is a bit of a grey area. At least we avoid using Hibernate-specific API.

Original pull request #2412
See #2330
Closes #2391

Author: mp911de

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2008-2021 the original author or authors.
+ * Copyright 2008-2022 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -32,8 +32,8 @@
 import org.eclipse.persistence.queries.ScrollableCursor;
 import org.hibernate.ScrollMode;
 import org.hibernate.ScrollableResults;
-import org.hibernate.metamodel.model.domain.spi.IdentifiableTypeDescriptor;
 import org.hibernate.proxy.HibernateProxy;
+
 import org.springframework.data.util.CloseableIterator;
 import org.springframework.lang.Nullable;
 import org.springframework.transaction.support.TransactionSynchronizationManager;
@@ -103,9 +103,7 @@ public Object getIdentifierFrom(Object entity) {
 		 */
 		@Override
 		public <T> Set<SingularAttribute<? super T, ?>> getIdClassAttributes(IdentifiableType<T> type) {
-			return type instanceof IdentifiableTypeDescriptor && ((IdentifiableTypeDescriptor<T>) type).hasIdClass()
-					? super.getIdClassAttributes(type)
-					: Collections.emptySet();
+			return type.hasSingleIdAttribute() ? Collections.emptySet() : super.getIdClassAttributes(type);
 		}
 
 		/*