MapStruct record to record mapping does not work

Question

I try to convert a Java record from one package to another.

@Mapper
public interface KriteriumMapper {

    KriteriumMapper INSTANCE = Mappers.getMapper(KriteriumMapper.class);
    de.model.Kriterium fromPersistenceRecord(Kriterium k);
}

package de.persistence.model.nontransactional;

public record Kriterium(String name, String crkSpaltenname) {}

To

package de.model;

public record Kriterium(String name, String crkSpaltenname) {}

But Mapstruct creates a mapper with an empty constructor for the new record, which is obviously not possible:

@Override
public de.Kriterium fromPersistenceRecord(de.persistence.model.Kriterium k) {
    if ( k == null ) {
        return null;
    }
    
    de.model.Kriterium kriterium = new de.Kriterium();
    
    return kriterium;
}

The Mapstruct version is 1.5.5.Final.

How to handle Java record-to-record mapping?

I'm expecting a mapper implementation with uses the regular all args constructor of a jave record.

Answer 1

You mix-up the package names, I have noticed you use more than 2 Kriterium classes:

• de.persistence.model.nontransactional.Kriterium
• de.persistence.model.Kriterium
• de.Kriterium

You want to double-check that the classes from the correct packages are used in the KriteriumMapper.

Don't forget to compile with the -parameters flag to enable generating metadata for reflection on method parameters (thanks to Rob Spoor).

Here is a minimum working sample of record-to-record mapping:

@Mapper
public interface KriteriumMapper {

    Kriterium2 fromPersistenceRecord(Kriterium k);
}

public record Kriterium(String name, String crkSpaltenname) {}

public record Kriterium2(String name, String crkSpaltenname) {}

Here is the generated implementation of KriteriumMapperImpl after compilation :

@Generated(
    value = "org.mapstruct.ap.MappingProcessor",
    date = "2023-10-02T18:18:30+0700",
    comments = "version: 1.5.5.Final, compiler: javac, environment: Java 17.0.1 (Oracle Corporation)"
)
public class KriteriumMapperImpl implementsKriteriumMapper {

    @Override
    public Kriterium2 fromPersistenceRecord(Kriterium k) {
        if ( k == null ) {
            return null;
        }

        String name = null;
        String crkSpaltenname = null;

        name = k.name();
        crkSpaltenname = k.crkSpaltenname();

        Kriterium2 kriterium2 = new Kriterium2( name, crkSpaltenname );

        return kriterium2;
    }
}