Why Replacing MyBatis with MyBatis‑Plus Can Break LocalDateTime Handling (and How to Fix It)

MyBatis Replacement with MyBatis‑Plus

Background

An old project uses MySQL 5.7.36, MyBatis 3.5.0, and mysql‑connector‑java 5.1.26.

A new developer finds MyBatis cumbersome and decides to replace it with MyBatis‑Plus.

MyBatis‑Plus Replaces MyBatis

A demo table tbl_order is created and populated with two rows.

The demo uses MyBatis‑Plus version 3.1.1 while keeping the original mysql‑connector‑java version.

First Failure

Running com.qsl.OrderTest#orderListAllTest throws an exception:

Conversion not supported for type java.time.LocalDateTime

The error originates from mysql‑connector‑java, which does not support LocalDateTime in version 5.1.26.

Support starts from version 5.1.37.

Root‑Cause Analysis

MyBatis 3.5.1 stopped handling LocalDateTime, delegating conversion to the JDBC driver. The older driver lacks support, causing the failure.

MyBatis‑Plus itself is not at fault; the version change introduced the regression.

Storm Approaches

After upgrading the connector to 5.1.37, the original error disappears, but inserting a record with a NULL timestamp triggers another exception.

Further investigation shows the driver still lacks full handling; upgrading to 5.1.42 finally resolves the issue.

Related Issue

The same problem appears in MyBatis‑Plus issue #1114. The choice of connection pool (HikariCP vs Druid) can affect the observed behavior.

Fixing an Unrelated Bug

Background

A file generation system validates that all primary files are generated before creating dependent files.

Pre‑Optimization Validation

The original logic considered the validation passed if *any* primary file existed, which violated business rules.

Optimized Validation

The logic was corrected to require *all* primary files to be present.

Production Incident

After deployment, a dependent file failed because a primary file’s identifier stored a filename string (e.g., abc_{yyyyMMdd}.txt) instead of a numeric ID, exposing the previous validation bug.

Conclusion

Component upgrades or code changes can have far‑reaching effects; thorough testing and awareness of version‑specific behavior are essential to avoid cascading failures.