JPA: Hibernate: updating of column with Converter class doesn't work

Question

I'm using a Converter class to store my entity field (type - Map<String, Object>) in MySql DB as a JSON text:

@Entity
@Table(name = "some_table")
public class SomeEntity {
    ...

    @Column(name = "meta_data", nullable = false)
    @Convert(converter = MetaDataConverter.class)
    Map<String, Object> metaData = null;
    ...
}

Here is the MetaDataConverter class:

@Converter
public class MetaDataConverter implements AttributeConverter<Map<String, Object>, String> {

    private final ObjectMapper objectMapper = new ObjectMapper();

    @Override
    public String convertToDatabaseColumn(Map<String, Object> metadata) {
        try {
            return objectMapper.writeValueAsString(metadata);
        } catch (Exception e) {
            ...
        }
    }

    @Override
    public Map<String, Object> convertToEntityAttribute(String dbData) {
        try {
            return objectMapper.readValue(dbData, Map.class);
        } catch (Exception e) {
            ...
        }
    }
}

Here is the my service class:

@Service
@RequiredArgsConstructor
@Transactional
public class MetaDataService {

    private final JpaRepository<MetaDataEntity, String> metaDataRepository;

    public MetaDataEntity updateOnlyMetadata(String someParameter, Map<String, Object> newMetaData) {
        MetaDataEntity metaDataEntity = metaDataRepository.findBySomeParameter(someParameter);
        metaDataEntity.setMetaData(newMetaData);
        return metaDataRepository.save(metaDataEntity);
    }
}

For the creation it works fine, but it doesn't work with the updating of the converted field. If i try to update only the metaData field the appropriate column in database is not updated. However, the metaData is updated in case of updating with the other entity fields.

I've already seen the same questions (JPA not updating column with Converter class and Data lost because of JPA AttributeConverter?), but i have not found the answer. Is there something like a standard or best practice for such a case?

FYI: For the CRUD operations i'm using the Spring Data JpaRepository class and its methhods.

Answer 1

I had a similar problem. i figure out that hibernate used the equals method to determine if one of attribute is dirty and then make an update.

you have two choices : implement correctly the equals method for the entity including the converted attribute

or

instead of using "Map" try to use "HashMap" as attribute type. the HashMap has an already implemented equals method and hibernate will use it