如果源不包含此列表，如何在目标中获取List的元素（用于映射）？

Question

我正在尝试映射下一个结构（在dozer中成功映射，与mapstruct有一些问题），源代码中缺少列表，如何在mapper中获取其第一个元素？目标类别：

    @Data
public class FirstLvl {
        protected List<SecondLvl> list;
        
        @Data
        public static class SecondLvl {
                protected FirstLvl.SecondLvl.ThirdLvl thirdLvl;

                @Data
                public static class ThirdLvl {
                        protected FourthLvl fourthLvl;
                }
        }
}

@Data
public class FourthLvl {
        protected FourthLvl.FithLvl fithLvl;

        @Data
        public static class FithLvl {

                protected String str1;
                protected String str2;

        }
}

资料来源：

@Data
public class FirstLvlDTO {
      protected FirstLvlDTO.SecondLvlDTO secondLvlDTO ;

        @Data
        public static class SecondLvlDTO  {
            protected FirstLvlDTO.SecondLvlDTO.ThirdLvlDTO thirdLvlDTO ;


                @Data
                public static class ThirdLvlDTO {

                        protected FourthLvlDTO fourthLvlDTO;
                }
        }

}

@Data
public class FourthLvlDTO  {

        protected String str1;

        protected String str2;

}

映射器和对象工厂：

@Mapper(uses = { ObjectFactory.class })
public interface FirstLvlDTOtoFirstLvl  {

@Mapping（target=“list[0].threeLvl.fourthLvl.fithLvl.str2”， source=“secondLvlDTO.thirdLvlDTO.fourthLvlDTO.str2”）

    FirstLvl toFirstLvl (FirstLvlDTO firstLvlDTO );
        
}

public class ObjectFactory {

    public FirstLvl createFirstLvl() {
        return new FirstLvl();
    }
    
    public FirstLvl.SecondLvl createFSLvl() {
        return new FirstLvl.SecondLvl();
    }
}

问题是我不知道如何获得列表的第一个元素(mapstruct中没有使用[]符号)。我可以将方法getlist0/setlist0添加到FirstLvl类中，以简单地返回列表的第一个元素(return list.get(0))，并在List 0 . third lvl . fourthlvl . fithlvl . str 2这样的映射器中使用它，但我不知道这是不是一个好主意，是否有可能做得更好

Answer 1

Mapstruct不支持多对一或一对多映射，这些映射需要手动实现。

在这里，您可以找到类的工作示例：

@Mapper
public abstract class LevelMapper {

    @Mapping( target = "secondLvlDTO", source = "list" )
    public abstract FirstLvlDTO map(FirstLvl lvl);

    // used by the manual implementation to continue mapping.
    @Mapping( target = "thirdLvlDTO.fourthLvlDTO", source = "thirdLvl.fourthLvl.fithLvl" )
    protected abstract SecondLvlDTO map(SecondLvl lvl);

    // manually implementation for getting the first object from the list and converting it.
    protected SecondLvlDTO getFirst(List<SecondLvl> list) {
        return map( list.get( 0 ) );
    }

// the reverse
    
    @Mapping( target = "list", source = "secondLvlDTO" )
    public abstract FirstLvl map(FirstLvlDTO lvl);

    // used by the manual implementation to continue mapping.
    @Mapping( target = "thirdLvl.fourthLvl.fithLvl", source = "thirdLvlDTO.fourthLvlDTO" )
    protected abstract SecondLvl map(SecondLvlDTO lvl);

    // manually implementation for creating the the list and filling it with the converted dto.
    protected List<SecondLvl> asList(SecondLvlDTO dto) {
        return Arrays.asList( map( dto ) ); // or any other way to create a list.
    }
}

Answer 2

我不确定我完全理解你的代码。我的方法应该是这样的。然而，您在列表中的类型似乎不匹配。

public interface TestMapper {

    @Mapping(target = "list0", ignore = true)
    @Mapping(target = "list", ignore = true)
    A toA(A1 a1);

    @AfterMapping
    default void mapperCode(@MappingTarget A a, A1 a1) {
        List<A.B> list = a.getList(); // target list requiures Type A.B 
        A1.B1 b1 = a1.getB1(); // source does have A1.B1 and not A.B as type
        // if your Types match set the list here manually like 
        // a.setList(List.of(a1.getB()));
    }

}

您的代码仅使用A、B、A1、B1，...。我建议你用真名。

编辑：

一个可行但非常丑陋的解决方案是手动操作。我不确定这是否对你有帮助。

public interface TestMapper {

@Mapping(target = "list", ignore = true)
FirstLvl map(FirstLvlDTO firstLvlDTO);

@AfterMapping
default void mapperCode(@MappingTarget FirstLvl firstLvl, FirstLvlDTO firstLvlDTO) {
    String str1 = firstLvlDTO.getSecondLvlDTO().getThirdLvlDTO().getFourthLvlDTO().getStr1();
    String str2 = firstLvlDTO.getSecondLvlDTO().getThirdLvlDTO().getFourthLvlDTO().getStr2();
    FirstLvl.SecondLvl secondLvl = new FirstLvl.SecondLvl();
    FirstLvl.SecondLvl.ThirdLvl thirdLvl = new FirstLvl.SecondLvl.ThirdLvl();
    secondLvl.setThirdLvl(thirdLvl);
    FourthLvl fourthLvl = new FourthLvl();
    thirdLvl.setFourthLvl(fourthLvl);
    FourthLvl.FithLvl fithLvl = new FourthLvl.FithLvl(str1, str2);
    fourthLvl.setFithLvl(fithLvl);
    firstLvl.setList(Arrays.asList(secondLvl));
}

}

@Data
public class FourthLvl {
protected FourthLvl.FithLvl fithLvl;

@Data
public static class FithLvl {

    public FithLvl(String str1, String str2){
        this.str1 = str1;
        this.str2 = str2;
    }

    protected String str1;
    protected String str2;

}

}