如何创建引用spring data rest/HATEOAS中已有子实体的新父实体

Question

在我的项目中，我有两个领域模型。父实体和子实体。父对象引用子对象的列表。（如帖子和评论）这两个实体都有他们的spring数据JPACrudepository

HTTP GET和PUT操作工作正常，并返回这些模型的良好HATEOS表示。

现在我需要一个特殊的RESTendpoint“创建一个引用一个或多个现有子实体的新父实体”。我想在请求的正文中以文本/uri-list的形式发布对孩子的引用，如下所示：

POST http://localhost:8080/api/v1/createNewParent
HEADER
  Content-Type: text/uri-list
HTTP REQUEST BODY:
   http://localhost:8080/api/v1/Child/4711
   http://localhost:8080/api/v1/Child/4712
   http://localhost:8080/api/v1/Child/4713

如何实现此Rest终结点？这是我目前所尝试的：

 @Autowired
 ParentRepo parentRepo  // Spring Data JPA repository for "parent" entity


 @RequestMapping(value = "/createNewParent", method = RequestMethod.POST)
 public @ResponseBody String createNewParentWithChildren(
    @RequestBody Resources<ChildModel> childList,                         
    PersistentEntityResourceAssembler resourceAssembler
) 
{
   Collection<ChildModel> childrenObjects = childList.getContent()

   // Ok, this gives me the URIs I've posted
   List<Link> links = proposalResource.getLinks();

   // But now how to convert these URIs to domain objects???
   List<ChildModel> listOfChildren = ... ???? ...

   ParentModel newParnet = new ParentModel(listOfChildren)
   parentRepo.save(newParent)

}

参考/相关https://github.com/spring-projects/spring-hateoas/issues/292




Answer 1

我也有同样的问题。这个问题有点老，但我找到了另一个解决方案：

事实上，您必须在父级上强制合并，但在创建时调用peris。您可以通过使用空的子列表保存父项，将子项添加到列表中，然后再次保存：

List<ChildModel> listOfChildren = ... ???? ...

ParentModel newParnet = new ParentModel()
parent = parentRepo.save(newParent)
parent.getChilds().addAll(listOfChildren)
parentRepo.save(parent)

要有权合并，您必须对自定义回购进行编码：

public interface PollModelRepositoryCustom {
    public PollModel merge(PollModel poll);
}

及其实施

@Repository
public class PollModelRepositoryCustomImpl implements PollModelRepositoryCustom {
    @PersistenceContext
    private EntityManager entityManager;

    public PollModel merge(PollModel poll) {
        return entityManager.merge(poll);
    }
}

然后，您可以调用：括号回购。（new家长）而不是括号epo.save（new家长）

Answer 2

另一个需要考虑的相关问题是：当我想保存父实体时，我不想以任何方式触摸、保存或更改已经存在的子实体。这在JPA中并不容易。因为JPA还将（尝试）保留从属子实体。此操作失败，但有一个例外：

javax.persistence.PersistenceException: org.hibernate.PersistentObjectException: detached entity passed to persist:

为了避免这种情况，必须将子实体合并到jpasave（）调用的transactin中。我发现在一个事务中有两个实体的唯一方法是创建一个单独的@Services，标记为@Transactional。看起来完全是过度的杀戮和过度的冒险。

这是我的密码：

波尔控制器。java//父实体的自定义RESTendpoint

@BasePathAwareController
public class PollController {

@RequestMapping(value = "/createNewPoll", method = RequestMethod.POST)
public @ResponseBody Resource createNewPoll(
    @RequestBody Resource<PollModel> pollResource, 
    PersistentEntityResourceAssembler resourceAssembler
) throws LiquidoRestException
{
  PollModel pollFromRequest = pollResource.getContent();
  LawModel proposalFromRequest = pollFromRequest.getProposals().iterator().next();             // This propsal is a "detached entity". Cannot simply be saved.
  //jpaContext.getEntityManagerByManagedType(PollModel.class).merge(proposal);      // DOES NOT WORK IN SPRING.  Must handle transaction via a seperate PollService class and @Transactional annotation there.

  PollModel createdPoll;
  try {
    createdPoll = pollService.createPoll(proposalFromRequest, resourceAssembler);
  } catch (LiquidoException e) {
    log.warn("Cannot /createNewPoll: "+e.getMessage());
    throw new LiquidoRestException(e.getMessage(), e);
  }

  PersistentEntityResource persistentEntityResource = resourceAssembler.toFullResource(createdPoll);

  log.trace("<= POST /createNewPoll: created Poll "+persistentEntityResource.getLink("self").getHref());

  return persistentEntityResource;   // This nicely returns the HAL representation of the created poll
}

PollService。java//用于事务处理

@Service
public class PollService {

    @Transactional    // This should run inside a transaction (all or nothing)
    public PollModel createPoll(@NotNull LawModel proposal, PersistentEntityResourceAssembler resourceAssembler) throws LiquidoException {
    //===== some functional/business checks on the passed enties (must not be null etc)
    //[...]

    //===== create new Poll with one initial proposal
    log.debug("Will create new poll. InitialProposal (id={}): {}", proposal.getId(), proposal.getTitle());
    PollModel poll = new PollModel();
    LawModel proposalInDB = lawRepo.findByTitle(proposal.getTitle());  // I have to lookup the proposal that I already have

    Set<LawModel> linkedProposals = new HashSet<>();
    linkedProposals.add(proposalInDB);
    poll.setProposals(linkedProposals);

    PollModel savedPoll = pollRepo.save(poll);

    return savedPoll;
}