[hibernate#929] Refactor id generation for MySQL

MySQL always returns an id of type Long.
This commit changes an hack that was affecting all dbs
and preventing H2 to read identity id of type Integer or Short

hibernate-reactive-core/src/main/java/org/hibernate/reactive/logging/impl/Log.java

@@ -104,8 +104,8 @@ public interface Log extends BasicLogger {
 	@Message(id = 34, value = "The database returned no natively generated identity value")
 	HibernateException noNativelyGeneratedValueReturned();
 
-	@Message(id = 35, value = "The database can only generate identifiers of type Long")
-	HibernateException nativelyGeneratedValueMustBeLong();
+	@Message(id = 35, value = "The database can only generate identifiers of type Long: the id %1$d cannot be cast to %2$s ")
+	HibernateException nativelyGeneratedValueMustBeLong(Long id, @FormatWith(ClassFormatter.class) Class<?> idClass);
 
 	@Message(id = 356, value = "Wrong entity type!")
 	HibernateException wrongEntityType();

hibernate-reactive-core/src/main/java/org/hibernate/reactive/persister/entity/impl/ReactiveAbstractEntityPersister.java

@@ -393,11 +393,6 @@ default CompletionStage<Serializable> insertReactive(
 		} );
 
 		Class<?> idClass = delegate().getIdentifierType().getReturnedClass();
-		if ( idClass.equals(Integer.class) || idClass.equals(Short.class) ) {
-			// since on MySQL we can only retrieve Long values, adjust to Long
-			// id will be cast back to the right type by castToIdentifierType()
-			idClass = Long.class;
-		}
 		return getReactiveConnection( session )
 				//Note: in ORM core there are other ways to fetch the generated identity:
 				//      getGeneratedKeys(), or an extra round select statement. But we

hibernate-reactive-core/src/main/java/org/hibernate/reactive/pool/impl/SqlClientConnection.java

@@ -309,10 +309,19 @@ public CompletionStage<Void> close() {
 	private static <T> T getLastInsertedId(RowSet<Row> rows, Class<T> idClass, String idColumnName) {
 		final Long mySqlId = rows.property( MYSQL_LAST_INSERTED_ID );
 		if ( mySqlId != null ) {
+			// MySQL will return a Long for any of these types
 			if ( Long.class.equals( idClass ) ) {
 				return (T) mySqlId;
 			}
-			throw LOG.nativelyGeneratedValueMustBeLong();
+			if ( Integer.class.equals( idClass )
+					&& mySqlId <= Integer.MAX_VALUE ) {
+				return (T) mySqlId;
+			}
+			if ( Short.class.equals( idClass )
+					&& mySqlId <= Short.MAX_VALUE) {
+				return (T) mySqlId;
+			}
+			throw LOG.nativelyGeneratedValueMustBeLong( mySqlId, idClass );
 		}
 		final Row oracleKeys = rows.property( ORACLE_GENERATED_KEYS );
 		if ( oracleKeys != null ) {