Why MyBatis‑Plus Migration Fails: LocalDateTime Conversion and Connector Version Issues

The original system was built on MySQL 5.7.36, MyBatis 3.5.0 and mysql‑connector‑java 5.1.26. A new developer found MyBatis cumbersome and decided to replace it with MyBatis‑Plus 3.1.1 while keeping the other components unchanged.

Initial Migration Attempt

A demo table tbl_order with two rows was created, and a simple MyBatis‑Plus demo was built to simulate the migration. Running the test method com.qsl.OrderTest#orderListAllTest produced an exception:

Conversion not supported for type java.time.LocalDateTime

The stack trace highlighted that the java.time.LocalDateTime type could not be converted, and the culprit was identified as the JDBC driver: mysql‑connector‑java 5.1.26 does not support this type.

Root‑Cause Analysis

MyBatis 3.5.0 handled LocalDateTime internally, converting java.sql.Timestamp to the Java 8 time class. Starting with MyBatis 3.5.1, this handling was removed; conversion is delegated to the JDBC driver. Since the driver version in use (5.1.26) lacks support for LocalDateTime, the conversion fails.

Inspection of the driver’s supported types (via the driver’s documentation and a quick test) confirmed that LocalDateTime, LocalDate and LocalTime are absent until mysql‑connector‑java 5.1.37.

Fixing the Issue

Upgrading the JDBC driver to version 5.1.37 (or later) restores support for the missing types. After the upgrade, re‑running com.qsl.OrderTest#orderListAllTest succeeds and returns correct query results.

Further Complications

When the project later upgraded MyBatis to 3.5.1 (implicitly via a dependency change), the same error resurfaced because the newer MyBatis no longer performed the conversion. The solution remained the same: use a driver version that supports Java 8 time types, e.g., mysql‑connector‑java 5.1.42.

Lessons Learned

Component upgrades can have cascading effects; a change in one library may expose incompatibilities in another.

Always verify that the JDBC driver version matches the expectations of the ORM framework, especially regarding Java 8 date‑time support.

When troubleshooting, start from the stack trace, identify the failing component, and check its version compatibility.

In summary, the migration failure was caused by MyBatis 3.5.1 delegating LocalDateTime conversion to the JDBC driver, which in versions prior to 5.1.37 does not support the type. Updating the driver resolves the problem.