HHH-18728 - Allow mixed discriminator-value mappings for ANY

HHH-18729 - Allow custom strategy for implicit discriminator-value determination for ANY

Author: sebersole

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

@@ -22,6 +22,9 @@
 import java.util.function.Consumer;
 import java.util.function.Function;
 
+import static org.hibernate.persister.entity.DiscriminatorHelper.NOT_NULL_DISCRIMINATOR;
+import static org.hibernate.persister.entity.DiscriminatorHelper.NULL_DISCRIMINATOR;
+
 /**
  * @author Steve Ebersole
  */
@@ -60,6 +63,14 @@ private ImplicitDiscriminatorStrategy resolveImplicitValueStrategy(ImplicitDiscr
 				return FullNameImplicitDiscriminatorStrategy.FULL_NAME_STRATEGY;
 			}
 		}
+		else {
+			if ( explicitValueMappings.containsKey( NOT_NULL_DISCRIMINATOR ) ) {
+				if ( implicitValueStrategy != null ) {
+					// we will ultimately not know how to handle "implicit" values which are non-null
+					throw new HibernateException( "Illegal use of ImplicitDiscriminatorStrategy with explicit non-null discriminator mapping: " + discriminatorRole.getFullPath() );
+				}
+			}
+		}
 		return implicitValueStrategy;
 	}
 
@@ -80,6 +91,10 @@ public Map<String, DiscriminatorValueDetails> getDetailsByEntityName() {
 
 	@Override
 	public DiscriminatorValueDetails getDetailsForDiscriminatorValue(Object relationalValue) {
+		if ( relationalValue == null ) {
+			return detailsByValue.get( NULL_DISCRIMINATOR );
+		}
+
 		final DiscriminatorValueDetails existing = detailsByValue.get( relationalValue );
 		if ( existing != null ) {
 			return existing;
@@ -109,6 +124,11 @@ else if ( getRelationalJavaType() instanceof CharacterJavaType ) {
 			}
 		}
 
+		final DiscriminatorValueDetails nonNullMatch = detailsByValue.get( NOT_NULL_DISCRIMINATOR );
+		if ( nonNullMatch != null ) {
+			return nonNullMatch;
+		}
+
 		throw new HibernateException( "Unknown discriminator value (" + discriminatorRole.getFullPath() + ") : " + relationalValue );
 	}