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Java / MapStruct Java Interview questions part 2

How do you troubleshoot an "Unmapped target property" warning?

This warning means a property on the target type has no source property, @Mapping rule, or usable conversion method that MapStruct could find. Working through it is mostly a process of elimination.

  1. Check the exact property name in the warning against the source type - a small spelling or casing difference will break automatic matching.
  2. If the names genuinely differ, add an explicit @Mapping(source = "...", target = "...").
  3. If the property should never come from the source, add @Mapping(target = "...", ignore = true) to document that intentionally.
  4. If it's a nested/complex type, confirm a matching conversion method exists or is reachable via uses.

Leaving it unresolved isn't necessarily wrong, but doing so silently invites bugs where a field is unintentionally left null in production.

A common cause of this warning is:
If a property should intentionally never be mapped, the fix is to:

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