Composite primary key not used at all in resource URI [DATAREST-846]

[spring-projects-issues]

Hendy Irawan opened DATAREST-846 and commented

With the following:

@Embeddable
public class SiteStatId implements Serializable {
    @Column(name = "watchedsite_id", nullable = false)
    public Long watchedSiteId;
    @Column(name = "creationtime", nullable = false)
    @Type(type = "org.jadira.usertype.dateandtime.joda.PersistentDateTime")
    public DateTime creationTime;

    public SiteStatId() {
    }

    public SiteStatId(String id) {
        final String[] split = id.split("_");
        this.watchedSiteId = Long.valueOf(split[0]);
        this.creationTime = new DateTime(split[1]);
    }

    public SiteStatId(Long watchedSiteId, DateTime creationTime) {
        this.watchedSiteId = watchedSiteId;
        this.creationTime = creationTime;
    }

    @Override
    public String toString() {
        return watchedSiteId + "_" + creationTime;
    }
}

GETing http://localhost:8080/api/siteStats gives:

{
  "_embedded": {
    "siteStats": [
      {
        "followerCount": 144,
        "followedByCount": 43,
        "postLikedByCount": 1,
        "postCount": 45,
        "creationTime": "2016-06-26T12:20:51.954Z",
        "watchedSite_id": 1,
        "_links": {
          "self": {
            "href": "http://localhost:8080/api/siteStats"
          },
          "siteStat": {
            "href": "http://localhost:8080/api/siteStats"
          },
          "watchedSite": {
            "href": "http://localhost:8080/api/siteStats/watchedSite"
          }
        }
      },
...

i.e. the (composite) ID is not used at all.

I've tried adding String constructor, and toString, to the ID class but that has no effect.

I've tried adding @Component BackendIdConverter and <del>it also doesn't work</del> it's not used by the collection REST output. But it is used when calling the individual resource URI, e.g. /api/siteStat/some_ID. But my problem here it's not shown in the collection JSON.

@Component
public class SiteStatIdConverter implements BackendIdConverter {

    @Override
    public Serializable fromRequestId(String id, Class<?> entityType) {
        return new SiteStatId(id);
    }

    @Override
    public String toRequestId(Serializable id, Class<?> entityType) {
        return id.toString();
    }

    @Override
    public boolean supports(Class<?> delimiter) {
        return SiteStat.class.equals(delimiter) || SiteStatId.class.equals(delimiter);
    }
}

I also tried adding @Component org.springframework.core.convert.converter implementation, that also doesn't work.

I suspect it has something to do with joda-time's DateTime field but maybe there's something else I'm missing. http://stackoverflow.com/questions/28700252/spring-data-rest-embeddedid-converters-registration#comment45738933_28700252 said that just a String constructor and toString is required, but it has no effect in my case.

Test case: https://github.com/soluvas/socmedmon/tree/spring-data-rest-composite-id-bug (branch spring-data-rest-composite-id-bug)

Related to DATAJPA-770

Related:

• Spring Data REST @Idclass not recognized: http://stackoverflow.com/a/31830586/122441
• Spring Data Rest @EmbeddedId converters registration: http://stackoverflow.com/q/28700252/122441
• Spring Data Rest @EmbeddedId cannot be constructed from Post Request: http://stackoverflow.com/q/36606251/122441

---

Affects: 2.4.4 (Gosling SR4)

Reference URL: https://github.com/soluvas/socmedmon/tree/spring-data-rest-composite-id-bug

3 votes, 5 watchers

[ruthst00]

This is a real bug in Spring Data REST, not a user mistake.

Tracing the code path for generating self links in a collection response:

1. DefaultSelfLinkProvider.createSelfLinkFor(Object instance) is called for each entity in the collection.
2. It calls entityIdentifierOrNull(instance), which uses Spring Data's PersistentEntity.getIdentifierAccessor(instance).getIdentifier() to extract the raw @EmbeddedId object (e.g., a SiteStatId instance).
3. That raw ID object is passed to RepositoryEntityLinks.linkForItemResource(Class<?> type, Object id), which calls idConverters.getPluginFor(type).toRequestId((Serializable) id, type).
4. This is where the BackendIdConverter is consulted — so the submitter's SiteStatIdConverter.toRequestId() should be called and should produce the correct string.

However, the bug manifests because of a subtlety in how PluginRegistry.getPluginFor(type) resolves the converter. The supports() method in the submitter's converter checks for SiteStat.class (the entity type), which is correct. But the issue is that the @EmbeddedId field's type (SiteStatId) is what Spring Data's IdentifierAccessor returns, and there's a known problem (referenced in the issue as DATAJPA-770) where Spring Data JPA's IdentifierAccessor for @EmbeddedId entities may return null or an unwrapped/incorrect value depending on the JPA provider state — causing the self link to fall back to the collection URI.

The submitter's observation that the BackendIdConverter works for direct item URIs (e.g., /api/siteStat/some_ID) but not for the collection output confirms this: the fromRequestId path (used for item lookups) works fine, but the toRequestId path (used for generating links in the collection) is never reached because getIdentifier() returns null for the embedded ID, causing the link generation to silently fall back to the collection root link.

cc @odrotbohm submitted this PR as potential fix to this issue