Why MyBatis‑Plus Upgrade Triggers LocalDateTime Errors and How to Fix Them

Background

The legacy project runs on MySQL 5.7.36, MyBatis 3.5.0, and mysql‑connector‑java 5.1.26. A developer replaces MyBatis with MyBatis‑Plus 3.1.1 while leaving the JDBC driver version unchanged.

Reproducing the issue

A simple tbl_order table is created and populated with two rows. The demo code resides in the repository

https://gitee.com/youzhibing/qsl-project/tree/master/play_it_safe

. Executing com.qsl.OrderTest#orderListAllTest throws:

org.springframework.dao.TransientDataAccessResourceException: Error attempting to get column 'pay_time' from result set.  Cause: java.sql.SQLException: Conversion not supported for type java.time.LocalDateTime

The stack trace points to a conversion failure for java.time.LocalDateTime.

Root‑cause analysis

MySQL‑Connector‑Java 5.1.26 does not support Java 8 time types. MyBatis 3.5.0 performed the conversion internally, but starting with MyBatis 3.5.1 the conversion is delegated to the JDBC driver, which then raises the exception.

Support for LocalDateTime, LocalDate and LocalTime was added in mysql‑connector‑java 5.1.37. The mismatch between MyBatis 3.5.1 (used indirectly by MyBatis‑Plus) and the old driver triggers the error.

Fix 1 – Upgrade mysql‑connector‑java to 5.1.37

Updating the driver to 5.1.37 eliminates the exception and the test returns the expected result.

Further issues after the first upgrade

Inserting a third record causes another failure because ResultSet.getTimestamp() returns NULL. Upgrading the driver further to 5.1.42 resolves this problem.

Additional investigation

The stack trace shows the failure originates from the JDBC driver, not from MyBatis‑Plus itself. An unrelated MyBatis‑Plus issue (issue‑1114) was discovered, but the root cause remains the driver’s lack of support for Java 8 time types. Different connection pools (e.g., Druid) may surface a different stack trace.

Lesson learned

When upgrading MyBatis to MyBatis‑Plus, ensure the JDBC driver version aligns with the MyBatis version’s handling of Java 8 time types. Comprehensive testing after any component upgrade is essential to avoid hidden incompatibilities.