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

Question

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":"[email protected]",
 "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":"[email protected]",
 "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.

• tewe: @zeroflagL I added the repositories and the relation
• Andrey Usov: Just a side note, it's better to remove @Transactional from your repository interfaces, first, because it's an interface, second, because the service layer should be the master of transaction. On a custom repo implementation, I would suggest to use @Transactional(propagation=SUPPORTS) to enable non-transactional reads if needed to better performance. See stackoverflow.com/questions/3120143/…

Answer 1

Just another workaround using a RelProvider:

1. Do not use @JsonTypeInfo

2. 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);
    }
   }
   

See also:

• https://jira.spring.io/browse/DATAREST-344
• http://docs.spring.io/spring-hateoas/docs/current/reference/html/#configuration.at-enable

• flaviut: It seems like RelProvider -> LinkRelationProvider: docs.spring.io/spring-hateoas/docs/current/api/org/…. I'm not going to edit this answer though since I'm not 100% certain.

Answer 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.

• Andrey Usov: I do not think it's Jackson issue. Good old Jackson works just fine. It's an issue with a custom Jackson URL serialiser from Spring DATA REST. Seems like this use-case is just not covered yet but there're workarounds.
• a better oliver: @aux The problem occurs while deserializing the request body, so what exactly's got the "custom Jackson URL serialiser" to do with that?
• Andrey Usov: Sorry, my misspelling, i meant deserializer, of course. By the way, this is already fixed in Spring Data REST 2.4 - see jira.spring.io/browse/DATAREST-662

Answer 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;
}