MapStruct：如何将所有属性映射到列表的第一个元素？

Question

我需要一个映射来实现此目的：

@Mapping(source = "a", target = "result.transactions[0].a"),
@Mapping(source = "b", target = "result.transactions[0].b"),
@Mapping(source = "c", target = "result.transactions[0].c"),
...
Response dataToResponse(DataModel model);

但这种语法不起作用（顺便说一句：这适用于 Spring Bean 包装器）。这样的解决方案只是一个半生不熟的解决方案：

@AsList
public <T> List<T> asList( T in ) {
    List<T> result = new ArrayList<T>();
    if ( in!=null ) {
       result.add(in);
   }
   return result;
}

这仅适用于一个属性，因为它总是为每个属性创建一个新列表。我不需要将每个属性映射到新列表的第一个元素。该列表必须重复使用，但我不知道这是如何工作的。实现这一目标的正确方法是什么？我想到了这样的事情：

@Mapping(source = "a", target = "transaction.a"),
@Mapping(source = "b", target = "transaction.b"),
@Mapping(source = "c", target = "transaction.c"),
...
Transaction dataToTransaction(DataModel model);

进而...

@Mapping([use Transaction from b4], target = "result");

但是我怎样才能从上面传递已经映射的字段呢？（我使用的是最新的最终版本1.1.0.Final）

Answer 1

我认为使用表达式是这里的解决方法：

public interface MyMapper {
    @Mapping(target = "subjectName", expression = "java(source.getCourses().get(0).getCourseName())")
    Target map(Source source);
} 

另请在此处查看更多信息： https ://github.com/mapstruct/mapstruct/issues/1321

在我的代码中我是这样做的：

@Mapping(expression = "java(player.getAddressBooks().get(0).getPostCode())", target = "postCode")
@Mapping(expression = "java(player.getAddressBooks().get(0).getCity())", target = "city")
@Mapping(expression = "java(player.getAddressBooks().get(0).getStreetNumber())", target = "streetNumber")
@Mapping(expression = "java(player.getAddressBooks().get(0).getStreetName())", target = "streetName")
@Mapping(expression = "java(player.getAddressBooks().get(0).getCountryISO())", target = "countryISO")

Answer 2

显然没有干净的解决方案。因此，我必须通过将以下映射排除到单独的映射器中来解决此问题：

@Mapping(source = "a", target = "transaction.a"),
@Mapping(source = "b", target = "transaction.b"),
@Mapping(source = "c", target = "transaction.c"),
Transaction dataToTransaction(DataModel model);

在主映射器中，我执行单独的映射器并通过表达式将其转换为列表：

@Mapping(expression = "java(Arrays.asList(SubMapper.INSTANCE.dataToTransaction(model)))", target = "result.transactions")