Better Support for Jackson's @JsonSubTypes

[harmenweber]

In our project, we have been using Immutables Criteria with a MongoDB backend for some time now. Recently, we tried to use Immutables Criteria for a model that uses Jackson's @JsonSubTypes for inheritance. We found that this use case is not fully supported yet.

We were able to make it work, but not without patching some of the Immutables Criteria code. And the patches we had to make are not ideal.

With this issue, I hope to

• either point the way to better support for models that use Jackson's `@JsonSubTypes',
• or learn how to store and retrieve polymorphic models in a better supported way, but still using Jackson.

To demonstrate the problems we face, I created the following commit 4cdc52c.
I added a simple polymorphic model and a test that tries to insert this model into a MongoDB and fetch again.

Here is the model:

@JsonTypeInfo(
    use = JsonTypeInfo.Id.NAME,
    include = JsonTypeInfo.As.PROPERTY,
    property = "@type")
@JsonSubTypes({
    @JsonSubTypes.Type(
        value = ImmutableErrorEvent.class,
        name = "org.immutables.criteria.jsonsubtypesmodel.ImmutableErrorEvent")
})
public interface Event<DATA> {
  @Criteria.Id
  UUID id();
  Instant instant();
  DATA data();
}

@Value.Immutable
@JsonSerialize(as = ImmutableErrorEvent.class)
@JsonDeserialize(as = ImmutableErrorEvent.class)
public interface ErrorEvent extends Event<Error> {
  @Override
  Error data();
}

@Value.Immutable
@JsonSerialize(as = ImmutableError.class)
@JsonDeserialize(as = ImmutableError.class)
public interface Error {
  String message();
  List<String> stacktrace();
}

And here is the test:

@ExtendWith(MongoExtension.class)
public class MongoEventTest {
  …

  @Test
  void insertAndFindOne() {
    ErrorEvent errorEvent = ImmutableErrorEvent.builder()
        .id(UUID.randomUUID())
        .instant(Instant.now().truncatedTo(ChronoUnit.MILLIS))
        .data(toError(getRandomException()))
        .build();
    
    this.syncWritable.insert(errorEvent);
    Event<?> loadedEvent = this.syncReadable.find(EventCriteria.event.id.is(errorEvent.id())).one();
    
    assertEquals(errorEvent, loadedEvent);
  }

  …
}

The test succeeds against an in-memory database. However, it fails when run against a real MongoDB instance with the following error message:

Caused by: java.lang.ClassCastException: class com.fasterxml.jackson.core.util.JsonParserSequence cannot be cast to class org.immutables.criteria.mongo.bson4jackson.Wrapper (com.fasterxml.jackson.core.util.JsonParserSequence and org.immutables.criteria.mongo.bson4jackson.Wrapper are in unnamed module of loader 'app')
	at org.immutables.criteria.mongo.bson4jackson.JacksonCodecs$1.deserialize(JacksonCodecs.java:101)
	at com.fasterxml.jackson.databind.deser.impl.MethodProperty.deserializeAndSet(MethodProperty.java:129)
	at com.fasterxml.jackson.databind.deser.BeanDeserializer.vanillaDeserialize(BeanDeserializer.java:310)

To run the test against a real local MongoDB instance, set the system property -Dmongo=mongodb://localhost as described in the MongoExtension.

The exception that occurs is due to the false assumption in the JacksonCodecs that the JsonParser can be cast into a Wrapper<BsonReader>. This assumption is false as soon as @JsonSubTypes is used, because Jackson wraps the BsonParser with a JsonParserSequence. As a result, the JsonParser can no longer be cast into a Wrapper<BsonReader>.

[elucash]

Thank you for reporting this! I cannot promise to look into this soon. I would encourage to create a PR as it seems like the cause of the issue and the fix is known