Migrating MyBatis to MyBatis-Plus: Debugging LocalDateTime Conversion Issues

An old Java project used MySQL 5.7, MyBatis 3.5.0 and mysql‑connector‑java 5.1.26. A new developer replaced MyBatis with MyBatis‑Plus 3.1.1, keeping the same connector version.

Running the test com.qsl.OrderTest#orderListAllTest caused an exception: Conversion not supported for type java.time.LocalDateTime . The root cause was identified as MyBatis 3.5.1 no longer handling LocalDateTime , LocalDate , and LocalTime conversions, delegating the task to the JDBC driver.

The mysql‑connector‑java 5.1.26 driver does not support these Java 8 time types. Upgrading the driver to 5.1.37 (or later 5.1.42) restored support and eliminated the exception.

Key steps demonstrated:

1. Insert a record into tbl_order :

INSERT INTO `tbl_order` VALUES (3, 'asdfgh', NULL, '2024-02-21 20:01:31.111', '2024-02-21 20:02:56.764');

2. Re‑run com.qsl.OrderTest#orderListAllTest after upgrading the connector.

The case highlights that changing a component (MyBatis → MyBatis‑Plus) can expose hidden incompatibilities in dependent libraries. Thorough testing and awareness of version‑specific behavior are essential when upgrading backend frameworks.