问题
Is there any way to use a @Projection interface as the default representation for a resource in SDR? Either through the SDR repositories or through a custom controller?
It used to be possible in a custom controller to do this by injecting a ProjectionFactory and using the createProjection method, but this has been broken by a recent Spring Data Rest update.
I would like to enforce a particular view on an entity, and the SDR projections seem like an ideal method for doing this, especially in the context of a HAL API, as opposed to writing hard DTO classes for a custom controller and mapping between them etc. Excerpt projections are not what I am after, as these only apply when looking at an associated resource.
回答1:
To answer my own question, there's now a couple of easyish ways to do this.
You can make SDR repository finders return projections by default:
public interface PersonRepository extends PagingAndSortingRepository<Person,Long> {
Set<PersonProjection> findByLastName(String lastName);
}
You can also selectively override responses that SDR would have handled for you by default by creating a custom Spring MVC controller with the @BasePathAwareController. You will need to inject the ProjectionFactory and possibly the PagedResourcesAssembler if you're planning on providing a paged response.
@BasePathAwareController
public class CustomPersonController {
@Autowired
private ProjectionFactory factory;
@Autowired
private PersonRepository personRepository;
@Autowired
private PagedResourcesAssembler<PersonProjection> assembler;
@RequestMapping(value="/persons", method = RequestMethod.GET, produces = "application/hal+json")
public ResponseEntity<?> getPeople(Pageable pageable) {
Page<Person> people = personRepository.findAll(pageable);
Page<PersonProjection> projected = people.map(l -> factory.createProjection(PersonProjection.class, l));
PagedResources<Resource<PersonProjection>> resources = assembler.toResource(projected);
return ResponseEntity.ok(resources);
}
回答2:
No it is not possible out of the box. Excerpt projections are always used if a resource is embedded. And on a single resource you can provide the desired projection as a query param.
What you can do is to use Jackson Mixins to change the json representation.
You can find some good examples here: https://github.com/olivergierke/spring-restbucks/blob/master/src/main/java/org/springsource/restbucks/JacksonCustomizations.java
回答3:
I would like to suggest yet another solution.
I used custom controller as @adam suggested untill I had to PATCH a resource and get new representation back. There is no way to override save method of a repository to use a projection by default. Implementing custom controllers all the time brings some boilerplate into the project.
Since I already used ResourceProcessors I decided to apply default projection right inside those processors.
@Component
public class ProductResourceProcessor implements ResourceProcessor<Resource<Product>> {
@Autowired
private ProjectionFactory projectionFactory;
@Override
@SuppressWarnings("unchecked")
public Resource<Product> process(Resource<Product> resource) {
Product content = resource.getContent();
ProductInline projection = projectionFactory.createProjection(ProductInline.class, content);
Resource<ProductInline> result = new Resource<>(projection);
//copying and adding links
return (Resource) result;
}
}
The processor repacks the content of processing resource. Thsi way the projection is applied no matter which handler returned the resource as a response (GET, POST, PATCH anything).
The drawback of this approach is it assumes that spring-data-rest doesn't require that the type of the content would be the same after processing. That may change anytime in the future releases.
来源：https://stackoverflow.com/questions/33288486/using-a-spring-data-rest-projection-as-a-representation-for-a-resource-in-a-cus