`@JsonUnwrapped` fails for HibernateProxy instances

[jwgmeligmeyling]

@JsonUnwrapped fails for HibernateProxy instances. They are serialized as if the @JsonUnwrapped annotation was missing.

Work around:

Replace the object with its underlying implementation:

Hibernate.initialize(client);
this.client = (Client) ((HibernateProxy) client)
      .getHibernateLazyInitializer()
      .getImplementation();

Tested on the following dependencies:

[INFO] +- com.fasterxml.jackson.core:jackson-databind:jar:2.8.0:compile
[INFO] |  +- com.fasterxml.jackson.core:jackson-annotations:jar:2.8.0:compile
[INFO] |  \- com.fasterxml.jackson.core:jackson-core:jar:2.8.0:compile
[INFO] +- com.fasterxml.jackson.datatype:jackson-datatype-jsr310:jar:2.8.0:compile
[INFO] +- com.fasterxml.jackson.datatype:jackson-datatype-hibernate5:jar:2.8.0:compile
[INFO] +- com.fasterxml.jackson.datatype:jackson-datatype-jdk8:jar:2.8.0:compile

[cowtowncoder]

I don't doubt this happens, but a reproducible unit test would be very helpful.

[jwgmeligmeyling]

I am working on a test case. Meanwhile I am also trying to step through the code a bit.

[shakuzen]

@jwgmeligmeyling Isn't @JsonUnwrapped not working when HibernateProxySerializer is used the expected behavior as per the note in the JsonUnwrapped JavaDoc:

Also note that annotation only applies if

• Value is serialized as JSON Object (can not unwrap JSON arrays using this mechanism)
• Serialization is done using BeanSerializer, not a custom serializer
• No type information is added; if type information needs to be added, structure can not be altered regardless of inclusion strategy; so annotation is basically ignored.

[jwgmeligmeyling]

I see why the JsonUnwrapped serializer does not support HibernateProxies by default, but imho the HibernateProxySerializer should work around that limitation as working around Hibernate proxy quirks is quite the goal of this module.

[cowtowncoder]

PRs welcome!

Note: due to lack of development it is possible and perhaps likely this module will be deprecated and not maintained in future.

[odrotbohm]

We're running into this in DATAREST-1494. The ultimate place tthigs start to diverge compared to non-proxy rendering is UnwrappingBeanPropertyWriter.serializeAsField(…) in this clause:

if (!ser.isUnwrappingSerializer()) {
  gen.writeFieldName(_name);
}

HibernateProxySerializer doesn't override this method. I am assuming that call is made to not unwrap in situations described by @shakuzen (👋, by the way). Looking at the callers of this method, it feels like the method is not returning the definite decision whether the implementation will unwrap in this moment but rather whether it's generally capable of unwrapping. If that's correct, couldn't the HibernateProxySerializer override the method and return true?

Happy to provide a pull request.

[jwgmeligmeyling]

@odrotbohm that fix actually makes a lot of sense. I never had the time to finish this myself (probably have some old branch from years ago with a reproducer if I dig deep...). I'd say go ahead and see if the fix works! It sounds promising to me. I think we find out soon enough if unwrapped serialization is really limited to BeanSerializer instances, or just serializers that return true for isUnwrappingSerializer.

[odrotbohm]

I'd still wait for some input by @cowtowncoder to whether my interpretation is correct. 🙃

[cowtowncoder]

Without having (had time to) look(ed), that does sound reasonable. I'll add this issue to my "to evalute" list to have a look before finalizing 2.11.0.

[cowtowncoder]

@odrotbohm Ok. So, meaning of isUnwrappingSerializer() is not about whether serializer supports it as much as try to support unwrapping (bean) serializer. Changing that would not help here. However, this method:

 public JsonSerializer<T> unwrappingSerializer(NameTransformer unwrapper) { }

is what would be needed to "change" proxy serializer to unwrapping one. It would be relatively easy to change that to create standard unwrapping bean serializer; however, that would then not handle proxy part of handling. Instead Hibernate module would either add handling of unwrapped properties into proxy serializer itself, or, subclass UnwrappingBeanSerializer to do so.

This is doable but not a trivial change.

If anyone wants to tackle it, I can probably help. I think some other module does this but I am not sure which one (Afterburner module, perhaps).