处理@RepositoryRestResource中的m-to-n关系 [英] Dealing with m-to-n relations in @RepositoryRestResource

问题描述

我想在一个调用中创建另一个资源的子资源。这些资源有 @ManyToMany 关系：用户和群组。

I want to create a sub-resource of another resource in one call. These resources have a @ManyToMany relationship: Users and Groups.

我不想先创建一个用户，然后创建该组，然后在工作中显示该关系与Spring Data REST中的关系 - 仅仅因为我认为只有一个用户也与之相关联的资源本身不能存在，例如一个组。资源。为此，我需要一个单独的端点喜欢这个（这对我不起作用，否则我不会在这里）这会创建一个组，并在一个事务中设置关联的种子用户。

I do not want to create first a user, then the group and after that the relation as it is shown in Working with Relationships in Spring Data REST - simply because I think a resource that cannot exist on its own, such as a group, should only be created if at least one user is also associated with that resource. For this I require a single endpoint like this one (which is not working for me, otherwise I wouldn't be here) that creates a group and also sets the associated "seeding" user in one transaction.

目前，让这个为我工作的唯一方法是同步关系像这样手动：

Currently, the only way to make this work for me is to "synchronize" the relation manually like this:

public void setUsers(Set<AppUser> users) {
    users.forEach(u -> u.getGroups().add(this));
    this.users = users;
}

这将允许我

POST http://localhost:8080/groups

{
  "name": "Group X",
  "users": ["http://localhost:8080/users/1"]
}

<但是我的问题是，这对我来说感觉不对 - 它看起来似乎是一种解决方法而不是实际的Spring方式使这个要求起作用。那么..

but my problem with that is that this does not feel right to me - it does seem like a workaround and not the actual Spring-way to make this requirement work. So ..

我目前正在努力使用Spring的 @RepositoryRestResource创建关系资源。我想创建一个新组并将其与调用用户关联，如下所示：

I'm currently struggling with creating relational resources using Spring's @RepositoryRestResource. I want to create a new group and associate it with the calling user like this:

POST http://localhost:8080/users/1/groups

{
  "name": "Group X"
}

但唯一的结果是响应 204 No Content 。我不知道为什么。这可能与我的另一个问题有关，也可能没有关系（参见这里）我尝试通过在JSON有效负载中设置相关资源来实现相同目的 - 这也不起作用。

but the only result is the response 204 No Content. I have no idea why. This may or may not be related to another question of mine (see here) where I try to achieve the same by setting the relating resource in the JSON payload - that doesn't work either.

服务器端我收到以下错误：

Server side I am getting the following error:

tion$ResourceSupportHttpMessageConverter : Failed to evaluate Jackson deserialization for type [[simple type, class org.springframework.hateoas.Resources<java.lang.Object>]]: java.lang.NullPointerException

如果您需要请告诉我任何具体的代码。

Please let me know in case you need any specific code.

我添加 exported = false 到 @RepositoryRestResource of UserGroupRepository ：

@RepositoryRestResource(collectionResourceRel = "groups", path = "groups", exported = false)
public interface UserGroupRepository extends JpaRepository<UserGroup, Long> {
    List<UserGroup> findByName(@Param("name") String name);
}

我发送邮件：

PATCH http://localhost:8080/users/1

{
  "groups": [
    {
      "name": "Group X"
    }
  ]
}

但是，结果仍然是服务器端的 204 No Content 和 ResourceNotFoundException 。

However, the result is still just 204 No Content and a ResourceNotFoundException on the server side.

基本上，以下单元测试应该是工作，但我也可以回答为什么这不起作用，这也说明了如何正确完成。

Essentially, the following unit test is supposed to work but I can also live with an answer why this cannot work and which also shows how this is done correctly.

@Autowired
private TestRestTemplate template;

private static String USERS_ENDPOINT = "http://localhost:8080/users/";
private static String GROUPS_ENDPOINT = "http://localhost:8080/groups/";

// ..

@Test
@DirtiesContext(classMode = ClassMode.BEFORE_EACH_TEST_METHOD)
public void whenCreateUserGroup() {

    // Creates a user
    whenCreateAppUser();

    ResponseEntity<AppUser> appUserResponse = template.getForEntity(USERS_ENDPOINT + "1/", AppUser.class);
    AppUser appUser = appUserResponse.getBody();

    UserGroup userGroup = new UserGroup();
    userGroup.setName("Test Group");
    userGroup.setUsers(Collections.singleton(appUser));

    template.postForEntity(GROUPS_ENDPOINT, userGroup, UserGroup.class);

    ResponseEntity<UserGroup> userGroupResponse = template.getForEntity(GROUPS_ENDPOINT + "2/", UserGroup.class);

    Predicate<String> username = other -> appUser.getUsername().equals(other);

    assertNotNull("Response must not be null.", userGroupResponse.getBody());

    assertTrue("User was not associated with the group he created.",
            userGroupResponse.getBody().getUsers().stream()
                    .map(AppUser::getUsername).anyMatch(username));
}

然而，行

userGroup.setUsers(Collections.singleton(appUser)); 

将破坏此测试并返回 404 Bad Request 。

推荐答案

根据 SDR参考：

POST

POST

仅支持集合关联。向集合添加新元素。支持的媒体类型：

Only supported for collection associations. Adds a new element to the collection. Supported media types:

text / uri-list - 指向要添加到关联的资源的URI。

text/uri-list - URIs pointing to the resource to add to the association.

所以要将 group 添加到 user 尝试这样做：

So to add group to user try to do this:

POST http://localhost:8080/users/1/groups (with Content-Type:text/uri-list)
http://localhost:8080/groups/1

其他信息。

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