HHH-16593 allow mappedBy to refer to a non-association property

(get rid of a totally unnecessary error)

hibernate-core/src/main/java/org/hibernate/boot/model/internal/BinderHelper.java

@@ -1083,9 +1083,13 @@ public static void checkMappedByType(
 		if ( targetValue instanceof Collection ) {
 			toOne = (ToOne) ( (Collection) targetValue ).getElement();
 		}
-		else {
+		else if ( targetValue instanceof ToOne ) {
 			toOne = (ToOne) targetValue;
 		}
+		else {
+			// Nothing to check, EARLY EXIT
+			return;
+		}
 		final String referencedEntityName = toOne.getReferencedEntityName();
 		final PersistentClass referencedClass = persistentClasses.get( referencedEntityName );
 		PersistentClass ownerClass = propertyHolder.getPersistentClass();

hibernate-core/src/test/java/org/hibernate/orm/test/mapping/mappedBy/MappedByNonAssociationTest.java

@@ -0,0 +1,70 @@
+package org.hibernate.orm.test.mapping.mappedBy;
+
+import jakarta.persistence.Column;
+import jakarta.persistence.Entity;
+import jakarta.persistence.Id;
+import jakarta.persistence.OneToMany;
+import org.hibernate.Hibernate;
+import org.hibernate.testing.orm.junit.DomainModel;
+import org.hibernate.testing.orm.junit.SessionFactory;
+import org.hibernate.testing.orm.junit.SessionFactoryScope;
+import org.junit.jupiter.api.Test;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import static jakarta.persistence.CascadeType.PERSIST;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+@SessionFactory
+@DomainModel(annotatedClasses = {MappedByNonAssociationTest.Loan.class, MappedByNonAssociationTest.Extensions.class})
+public class MappedByNonAssociationTest {
+
+	@Test void test(SessionFactoryScope scope) {
+		Extensions ex = new Extensions();
+		ex.exExtensionDays = 3L;
+		ex.exNo = 2L;
+		ex.exLoanId = 4L;
+
+		Loan loan = new Loan();
+		loan.id = 4L;
+		loan.extensions.add(ex);
+
+		scope.inTransaction(s -> s.persist(loan));
+		Loan l1 = scope.fromTransaction(s -> {
+			Loan ll = s.get(Loan.class, loan.id);
+			Hibernate.initialize(ll.extensions);
+			return ll;
+		});
+		assertEquals( 1, l1.extensions.size() );
+		assertEquals( loan.id, l1.id );
+		assertEquals( ex.exLoanId, l1.extensions.get(0).exLoanId );
+		Loan l2 = scope.fromSession(s -> s.createQuery("from Loan join fetch extensions", Loan.class).getSingleResult());
+		assertEquals( 1, l2.extensions.size() );
+		assertEquals( loan.id, l2.id );
+		assertEquals( ex.exLoanId, l2.extensions.get(0).exLoanId );
+	}
+
+	@Entity(name="Loan")
+	static class Loan {
+		@Id
+		@Column(name = "LOAN_ID")
+		private Long id;
+
+		@OneToMany(cascade = PERSIST, mappedBy = "exLoanId")
+		private List<Extensions> extensions = new ArrayList<>();
+	}
+
+	@Entity(name="Extensions")
+	static class Extensions  {
+		@Id
+		@Column(name = "EX_LOAN_ID")
+		private Long exLoanId;
+		@Id
+		@Column(name = "EX_NO")
+		private Long exNo;
+		@Column(name = "EX_EXTENSION_DAYS")
+		private Long exExtensionDays;
+	}
+
+}