我有父母(产品)和孩子(书,家具),并想将产品实体映射到产品DTO。如您所见,产品已映射并存储在数据库的单个表中。如何映射具有其子级额外详细信息的父产品?
实体
@Entity
@Table(name = "product")
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
public class Product {
@Id
private long id;
private String productName;
}
@Entity
@DiscriminatorValue("Book")
public class Book extends Product {
private String author;
...
}
@Entity
@DiscriminatorValue("Furniture")
public class Furniture extends Product {
String color;
...
}
DTO
public class ProductDto {
private long id;
private String productName;
...
}
public class BookDto extends ProductDto {
private String author;
...
}
public class FurnitureDto extends ProductDto {
String color;
...
}
映射器
@Mapper(uses = {BookMapper.class,FurnitureMapper.class})
public interface ProductMapper {
ProductDto productToProductDto(Product product);
Product productDtoToProduct(ProductDto productDto);
}
@Mapper
public interface BookMapper {
BookDto bookToBookDto(Book book);
Book bookDtoToBook(BookDto bookDto);
}
@Mapper
public interface FurnitureMapper {
FurnitureDto furnitureToFurnitureDto(Furniture furniture);
Furniture furnitureDtoToFurniture(FurnitureDto furnitureDto);
}
服务
@Service
public class ProductServiceImpl implements ProductService {
@Autowired
ProductRepository productRepository;
@Autowired
ProductMapper productMapper;
@Override
public List<ProductDto> getAllProducts() {
List<ProductDto> listOfProducts = new ArrayList<>();
productRepository.findAll().forEach(i ->
listOfProducts.add(productMapper.productToProductDto(i)));
return listOfProducts;
}
}
已编辑
将产品实体映射到产品dto后,得到以下结果。它不绑定数据,也不包括其子级属性。上面的映射器部分正确吗?
[
{
"id": 0,
"productName": null
},
{
"id": 0,
"productName": null
},
...
]
但是结果应该像下面这样:
[
{
"id": 11,
"productName": ABC,
"author":"James"
},
{
"id": 22,
"productName": XYZ,
"color":"Oak"
},
...
]
没有干净的方法可以做到这一点。原因在于Java的编译时方法选择。但是有一种使用访客模式的干净方法。
在迭代包含不同类型(产品,书籍,家具)的实体列表时,需要为每种类型调用不同的映射方法(即,不同的MapStruct映射器)。
除非您instanceof
按照Amir的建议进行操作,并明确选择映射器,否则您需要使用方法重载来为每个实体类调用不同的映射方法。问题是Java将在编译时选择重载的方法,此时,编译器仅看到Product
对象列表(存储库方法返回的对象)。MapStruct或Spring或您自己的自定义代码尝试执行此操作并不重要。这也是为什么ProductMapper
总是调用your的原因:它是在编译时可见的唯一类型。
由于我们需要手动选择正确的映射器,因此我们可以选择哪种方法更清洁或更可维护。这绝对是有根据的。
我的建议是按以下方式使用访客模式(实际上是它的一种变体):
为需要映射的实体引入一个新接口:
public interface MappableEntity {
public ProductDto map(EntityMapper mapper);
}
您的实体将需要实现此接口,例如:
public class Book extends Product implements MappableEntity {
//...
@Override
public ProductDto map(EntityMapper mapper) {
return mapper.map(this);//This is the magic part. We choose which method to call because the parameter is this, which is a Book!
}
}
EntityMapper是访问者接口:
public interface EntityMapper {
ProductDto map(Product entity);
BookDto map(Book entity);
FurnitureDto map(Furniture entity);
// Add your next entity here
}
最后,您需要MasterMapper:
// Not a class name I'm proud of
public class MasterMapper implements EntityMapper {
// Inject your mappers here
@Override
public ProductDto map(Product product) {
ProductMapper productMapper = Mappers.getMapper(ProductMapper.class);
return productMapper.map(product);
}
@Override
public BookDto map(Book product) {
BookMapper productMapper = Mappers.getMapper(BookMapper.class);
return productMapper.map(product);
}
@Override
public FurnitureDto map(Furniture product) {
FurnitureMapper productMapper = Mappers.getMapper(FurnitureMapper.class);
return productMapper.map(product);
}
// Add your next mapper here
}
您的服务方法将如下所示:
MasterMapper mm = new MasterMapper();
List<Product> listOfEntities = productRepository.findAll();
List<ProductDto> listOfProducts = new ArrayList<>(listOfEntities.size());
listOfEntities.forEach(i -> {
if (i instanceof MappableEntity) {
MappableEntity me = i;
ProductDto dto = me.map(mm);
listOfProducts.add(dto);
} else {
// Throw an AssertionError during development (who would run server VMs with -ea ?!?!)
assert false : "Can't properly map " + i.getClass() + " as it's not implementing MappableEntity";
// Use default mapper as a fallback
final ProductDto defaultDto = Mappers.getMapper(ProductMapper.class).map(i);
listOfProducts.add(defaultDto);
}
});
return listOfProducts;
您可以放心地忽略Mappers.getMapper()
调用:由于该问题与Spring无关,因此我为简化起见在GitHub上使用MapStruct的工厂创建了一个工作示例。您只需使用CDI注入映射器即可。
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