HHH-18147 Hibernate fails to persist an entity when a natural id association is a proxy

Author: dreab8

hibernate-core/src/main/java/org/hibernate/metamodel/mapping/internal/ToOneAttributeMapping.java

@@ -64,6 +64,8 @@
 import org.hibernate.persister.entity.EntityPersister;
 import org.hibernate.persister.entity.JoinedSubclassEntityPersister;
 import org.hibernate.property.access.spi.PropertyAccess;
+import org.hibernate.proxy.HibernateProxy;
+import org.hibernate.proxy.LazyInitializer;
 import org.hibernate.spi.EntityIdentifierNavigablePath;
 import org.hibernate.spi.NavigablePath;
 import org.hibernate.spi.TreatedNavigablePath;
@@ -2365,6 +2367,10 @@ private Object extractValue(Object domainValue, SharedSessionContractImplementor
 		}
 
 		if ( referencedPropertyName != null ) {
+			final LazyInitializer lazyInitializer = HibernateProxy.extractLazyInitializer( domainValue );
+			if ( lazyInitializer != null ) {
+				domainValue = lazyInitializer.getImplementation();
+			}
 			assert getAssociatedEntityMappingType()
 					.getRepresentationStrategy()
 					.getInstantiator()