How to reference an entity with inheritance in Spring Data REST when POSTing new entity?

问题

I have entities with joined inheritance:

Supporter

@Entity
@Inheritance(strategy=InheritanceType.JOINED)
@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "supporterType")
@JsonSubTypes({
    @JsonSubTypes.Type(value = PersonSupporterEntity.class, name = "PERSON"),
    @JsonSubTypes.Type(value = CompanySupporterEntity.class, name = "COMPANY")
})
@DiscriminatorColumn(name="supporter_type")
@Table(name = "supporter")
public class SupporterEntity extends UpdatableEntity {
    private long id;
    private SupporterType supporterType;
    private PartnerEntity partner;
...
}

PersonSupporter

@Entity
@DiscriminatorValue("PERSON")
@Table(name = "person_supporter")
public class PersonSupporterEntity extends SupporterEntity {
...
}

CompanySupporter

@Entity
@DiscriminatorValue("COMPANY")
@Table(name = "company_supporter")
public class CompanySupporterEntity extends SupporterEntity {
...
}

I have another entity which references SupporterEntity

@Entity
@Table(name = "contact")
public class ContactEntity extends UpdatableEntity {

    private long id;
    private SupporterEntity supporter;
...
    @ManyToOne // same error with @OneToOne
    @JoinColumn(name = "supporter_id", referencedColumnName = "id", nullable = false)
    public SupporterEntity getSupporter() {
        return supporter;
    }
...
}

Repositories

@Transactional
@RepositoryRestResource(collectionResourceRel = "supporters", path = "supporters")
public interface SupporterEntityRepository extends JpaRepository<SupporterEntity, Long> {

    @Transactional(readOnly = true)
    @RestResource(path = "by-partner", rel = "by-partner")
    public Page<SupporterEntity> findByPartnerName(@Param("name") String name, Pageable pageable);
}

@Transactional
@RepositoryRestResource(collectionResourceRel = "person_supporters", path = "person_supporters")
public interface PersonSupporterEntityRepository extends JpaRepository<PersonSupporterEntity, Long> {

}

@Transactional
@RepositoryRestResource(collectionResourceRel = "company_supporters", path = "company_supporters")
public interface CompanySupporterEntityRepository extends JpaRepository<CompanySupporterEntity, Long> {

}

@Transactional
@RepositoryRestResource(collectionResourceRel = "contacts", path = "contacts")
public interface ContactEntityRepository extends JpaRepository<ContactEntity, Long> {

    @Transactional(readOnly = true)
    @RestResource(path = "by-supporter", rel = "by-supporter")
    public ContactEntity findBySupporterId(@Param("id") Long id);
}

I use Spring Boot, Spring Data REST, Spring Data JPA, Hibernate, Jackson. When I try to create a new ContactEntity with a post request like this:

{
   "supporter":"/supporters/52",
   "postcode":"1111",
   "city":"Test City 1",
   "address":"Test Address 1",
   "email":"test1@email.com",
   "newsletter":true
}

I get this exception:

Caused by: com.fasterxml.jackson.databind.JsonMappingException: Unexpected token (VALUE_STRING), expected FIELD_NAME: missing property 'supporterType' that is to contain type id  (for class com.facer.domain.supporter.SupporterEntity)
 at [Source: HttpInputOverHTTP@4321c221; line: 1, column: 2] (through reference chain: com.facer.domain.supporter.ContactEntity["supporter"])
at com.fasterxml.jackson.databind.JsonMappingException.from(JsonMappingException.java:148) ~[jackson-databind-2.4.4.jar:2.4.4]

After 2 days of debugging I found a way, but I kinda guessed it. So if I post it like this:

{
   "supporter":{
      "supporterType":"PERSON",
      "id":"52"
   },
   "postcode":"1111",
   "city":"Test City 1",
   "address":"Test Address 1",
   "email":"test1@email.com",
   "newsletter":true
}

It works, but I don't know why. What's wrong with the other request? It works like that everywhere else when the referenced entity does not have inheritance.

回答1:

Just another workaround using a RelProvider:

Do not use @JsonTypeInfo

Create a RelProvider for SupporterEntity sub-classes

@Component
@Order(Ordered.HIGHEST_PRECEDENCE)
public class SupporterEntityRelProvider implements RelProvider {

  @Override
  public String getCollectionResourceRelFor(final Class<?> type) {
    return "supporters";
  }

  @Override
  public String getItemResourceRelFor(final Class<?> type) {
    return "supporter";
  }

  @Override
  public boolean supports(final Class<?> delimiter) {
    return org.apache.commons.lang3.ClassUtils.isAssignable(delimiter, SupporterEntity.class);
  }
}

回答2:

It looks like a Jackson problem. To be specific, it's the following code in com.fasterxml.jackson.databind.deser.SettableBeanProperty:

if (_valueTypeDeserializer != null) {
   return _valueDeserializer.deserializeWithType(jp, ctxt, _valueTypeDeserializer);
}
return _valueDeserializer.deserialize(jp, ctxt);

Without inheritance _valueDeserializer.deserialize would be called which in turn runs some Spring code to convert the URI to a Supporter.

With inheritance _valueDeserializer.deserializeWithType is called and vanilla Jackson, of course, expects an object, not a URI.

If supporter was nullable you could first POST to /contacts and then PUT the supporter's URI to /contacts/xx/supporter. Unfortunately I am not aware of any other solution.

回答3:

You should be able to workaround this by setting @JsonTypeInfo(use= JsonTypeInfo.Id.NONE) at the property/method level e.g.

Try with this:

@ManyToOne // same error with @OneToOne
@JoinColumn(name = "supporter_id", referencedColumnName = "id", nullable = false)
@JsonTypeInfo(use= JsonTypeInfo.Id.NONE)
public SupporterEntity getSupporter() {
    return supporter;
}

来源：https://stackoverflow.com/questions/29021221/how-to-reference-an-entity-with-inheritance-in-spring-data-rest-when-posting-new

标签

rest

jackson

spring-data-rest