如何在Spring Data REST项目中使用DTO? [英] How to work with DTO in Spring Data REST projects?
问题描述
Spring Data REST仅自动公开域对象.但是大多数情况下,我们必须处理数据传输对象.那么如何以SDR方式做到这一点呢?
一种使用 Spring Data REST 项目中的DTO >
工作示例是此处 >
实体
实体必须实施可识别的界面.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
}
投影
制作投影接口,存储库查询方法将返回:
public interface CategoryProjection {
Category getCategory();
Long getQuantity();
}
它将成为DTO的基础.在此示例中,DTO将代表Category
,而Product
的数量属于它.
存储库方法
Create方法返回投影:单个投影,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
从其界面实施DTO:
@Relation(value = "category", collectionRelation = "categories")
public class CategoryDto implements CategoryProjection {
private final Category category;
private final Long quantity;
// skipped
}
注释Relation
在Spring Data REST呈现对象时使用.
控制器
在RepositoryRestController
中添加可满足DTO请求的自定义方法:
@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);
}
}
从存储库收到投影时,我们必须完成从投影到DTO的最终转换
并将其包装"到 ResourceSupport 对象,然后再发送给客户端.
为此,我们使用辅助方法toResource
:创建一个新的DTO,为此对象创建必要的链接,
然后使用对象及其链接创建一个新的Resource
.
结果
请参阅邮递员网站上的API文档
单个DTO
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
}
}
Spring Data REST automates exposing only domain object. But most often we have to deal with Data Transfer Objects. So how to do this in SDR way?
An approach of how to work with DTO in Spring Data REST projects
The working example is here
Entities
Entities must implement the Identifiable interface. For example:
@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
}
Projections
Make a projection interface that repository query methods will return:
public interface CategoryProjection {
Category getCategory();
Long getQuantity();
}
It will be a basement for DTO. In this example DTO will represent a Category
and the number of Product
s are belong to it.
Repository methods
Create methods return the projection: a single one, a list of DTO and a paged list of DTO.
@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
Implement DTO from its interface:
@Relation(value = "category", collectionRelation = "categories")
public class CategoryDto implements CategoryProjection {
private final Category category;
private final Long quantity;
// skipped
}
Annotation Relation
is used when Spring Data REST is rendering the object.
Controller
Add custom methods to RepositoryRestController
that will serve requests of DTO:
@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);
}
}
When Projections are received from repository we must make the final transformation from a Projection to DTO
and 'wrap' it to ResourceSupport object before sending to the client.
To do this we use helper method toResource
: we create a new DTO, create necessary links for this object,
and then create a new Resource
with the object and its links.
Result
See the API docs on the Postman site
Singe DTO
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"
}
}
}
List of DTO
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"
}
}
}
Paged list of DTO
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
}
}
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