如何在Spring Data REST项目中使用DTO？

Question

Spring Data REST自动仅公开域对象.但大多数情况下,我们必须处理数据传输对象.那么如何以SDR方式做到这一点？

Answer 1

如何在Spring Data REST项目中使用DTO的方法

工作的例子在这里

实体

实体必须实现可识别的接口.例如:

@Entity
public class Category implements Identifiable<Integer> {

    @Id
    @GeneratedValue
    private final Integer id;

    private final String name;

    @OneToMany
    private final Set<Product> products = new HashSet<>();

    // skipped
}

@Entity
public class Product implements Identifiable<Integer> {

    @Id
    @GeneratedValue
    private final Integer id;

    private final String name;

    // skipped
}

预测

创建存储库查询方法将返回的投影接口:

public interface CategoryProjection {

    Category getCategory();
    Long getQuantity();
}

它将是DTO的地下室.在此示例中,DTO将表示a Category并且Products 的数量属于它.

存储库方法

创建方法返回投影:单个,DTO列表和DTO的分页列表.

@RepositoryRestResource
public interface CategoryRepo extends JpaRepository<Category, Integer> {

    @RestResource(exported = false)
    @Query("select c as category, count(p) as quantity from Category c join c.products p where c.id = ?1 group by c")
    CategoryProjection getDto(Integer categoryId);

    @RestResource(exported = false)
    @Query("select c as category, count(p) as quantity from Category c join c.products p group by c")
    List<CategoryProjection> getDtos();

    @RestResource(exported = false)
    @Query("select c as category, count(p) as quantity from Category c join c.products p group by c")
    Page<CategoryProjection> getDtos(Pageable pageable);
}

DTO

从其界面实现DTO:

@Relation(value = "category", collectionRelation = "categories")
public class CategoryDto implements CategoryProjection {

    private final Category category;
    private final Long quantity;

    // skipped
}

RelationSpring Data REST渲染对象时使用注释.

调节器

添加自定义方法RepositoryRestController将为DTO的请求提供服务:

@RepositoryRestController
@RequestMapping("/categories")
public class CategoryController {

    @Autowired private CategoryRepo repo;
    @Autowired private RepositoryEntityLinks links;
    @Autowired private PagedResourcesAssembler<CategoryProjection> assembler;

    /**
    * Single DTO
    */
    @GetMapping("/{id}/dto")
    public ResponseEntity<?> getDto(@PathVariable("id") Integer categoryId) {
        CategoryProjection dto = repo.getDto(categoryId);

        return ResponseEntity.ok(toResource(dto));
    }

    /**
    * List of DTO
    */
    @GetMapping("/dto")
    public ResponseEntity<?> getDtos() {
        List<CategoryProjection> dtos = repo.getDtos();

        Link listSelfLink = links.linkFor(Category.class).slash("/dto").withSelfRel();
        List<?> resources = dtos.stream().map(this::toResource).collect(toList());

        return ResponseEntity.ok(new Resources<>(resources, listSelfLink));
    }

    /**
    * Paged list of DTO
    */
    @GetMapping("/dtoPaged")
    public ResponseEntity<?> getDtosPaged(Pageable pageable) {
        Page<CategoryProjection> dtos = repo.getDtos(pageable);

        Link pageSelfLink = links.linkFor(Category.class).slash("/dtoPaged").withSelfRel();
        PagedResources<?> resources = assembler.toResource(dtos, this::toResource, pageSelfLink);

        return ResponseEntity.ok(resources);
    }

    private ResourceSupport toResource(CategoryProjection projection) {
        CategoryDto dto = new CategoryDto(projection.getCategory(), projection.getQuantity());

        Link categoryLink = links.linkForSingleResource(projection.getCategory()).withRel("category");
        Link selfLink = links.linkForSingleResource(projection.getCategory()).slash("/dto").withSelfRel();

        return new Resource<>(dto, categoryLink, selfLink);
    }
}

当从存储库收到预测时,我们必须从Projection到DTO进行最终转换,并在发送到客户端之前将其"换行"到ResourceSupport对象.为此,我们使用辅助方法toResource:我们创建一个新的DTO,为该对象创建必要的链接,然后Resource使用该对象及其链接创建一个新的.

结果

请参阅Postman网站上的API文档

烧STO

GET http://localhost:8080/api/categories/6/dto

{
    "category": {
        "name": "category1"
    },
    "quantity": 3,
    "_links": {
        "category": {
            "href": "http://localhost:8080/api/categories/6"
        },
        "self": {
            "href": "http://localhost:8080/api/categories/6/dto"
        }
    }
}

DTO列表

GET http://localhost:8080/api/categories/dto

{
    "_embedded": {
        "categories": [
            {
                "category": {
                    "name": "category1"
                },
                "quantity": 3,
                "_links": {
                    "category": {
                        "href": "http://localhost:8080/api/categories/6"
                    },
                    "self": {
                        "href": "http://localhost:8080/api/categories/6/dto"
                    }
                }
            },
            {
                "category": {
                    "name": "category2"
                },
                "quantity": 2,
                "_links": {
                    "category": {
                        "href": "http://localhost:8080/api/categories/7"
                    },
                    "self": {
                        "href": "http://localhost:8080/api/categories/7/dto"
                    }
                }
            }
        ]
    },
    "_links": {
        "self": {
            "href": "http://localhost:8080/api/categories/dto"
        }
    }
}

DTO的分页列表

GET http://localhost:8080/api/categories/dtoPaged

{
    "_embedded": {
        "categories": [
            {
                "category": {
                    "name": "category1"
                },
                "quantity": 3,
                "_links": {
                    "category": {
                        "href": "http://localhost:8080/api/categories/6"
                    },
                    "self": {
                        "href": "http://localhost:8080/api/categories/6/dto"
                    }
                }
            },
            {
                "category": {
                    "name": "category2"
                },
                "quantity": 2,
                "_links": {
                    "category": {
                        "href": "http://localhost:8080/api/categories/7"
                    },
                    "self": {
                        "href": "http://localhost:8080/api/categories/7/dto"
                    }
                }
            }
        ]
    },
    "_links": {
        "self": {
            "href": "http://localhost:8080/api/categories/dtoPaged"
        }
    },
    "page": {
        "size": 20,
        "totalElements": 2,
        "totalPages": 1,
        "number": 0
    }
}