How do you troubleshoot a MyBatis mapping exception?

MyBatis mapping errors generally fall into a handful of recurring categories, and working through them in a consistent order — from configuration issues to type mismatches — is usually faster than guessing at the root cause from the exception message alone.

1. Check the exception's root cause, not just the top-level message: MyBatis often wraps a lower-level JDBC or reflection exception, and the actual useful detail is usually in the cause chain.
2. Verify namespace and id correspondence: a mismatched mapper namespace or a statement id that doesn't exactly match the interface method name produces a "mapped statement not found" error.
3. Check for a BindingException (missing parameter): often caused by referencing a #{} placeholder that doesn't match an actual parameter name or object property, especially with multiple unnamed parameters missing @Param.
4. Verify resultMap/resultType field alignment: unmapped columns or mismatched types commonly cause silent null fields or a type conversion exception, rather than an obvious hard failure.
5. Check for duplicate mapped statement ids across mapper files, which MyBatis will reject at startup rather than at query time.

Enabling MyBatis's SQL logging (via a logging framework configuration, showing the actual executed SQL and bound parameters) is often the single most useful diagnostic step, since it reveals exactly what MyBatis is sending to the database — frequently exposing that the real problem is a subtly wrong SQL statement or misbound parameter rather than a deeper configuration issue.