Related entity rendered differently depending on JPA fetch type [DATAREST-1494]

[spring-projects-issues]

jvanheesch opened DATAREST-1494 and commented

Please see reference url for quick reproducer.

On branch master: curl [http://localhost:8080/books/] results in

{
  "timestamp": "2020-03-12T20:48:22.082+0000",
  "status": 500,
  "error": "Internal Server Error",
  "message": "Type definition error: [simple type, class org.hibernate.proxy.pojo.bytebuddy.ByteBuddyInterceptor]; nested exception is com.fasterxml.jackson.databind.exc.InvalidDefinitionException: No serializer found for class org.hibernate.proxy.pojo.bytebuddy.ByteBuddyInterceptor and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS) (through reference chain: org.springframework.hateoas.CollectionModel[\"_embedded\"]->java.util.Collections$UnmodifiableMap[\"books\"]->java.util.ArrayList[0]->org.springframework.data.rest.webmvc.json.PersistentEntityJackson2Module$PersistentEntityResourceSerializer$1[\"content\"]->com.github.jvanheesch.Book[\"author\"]->org.springframework.data.rest.webmvc.json.PersistentEntityJackson2Module$PersistentEntityResourceSerializer$1[\"content\"]->com.github.jvanheesch.Author$HibernateProxy$Co1jR6qK[\"hibernateLazyInitializer\"])",
  "path": "/books/"
}

For us this is currently non-blocking, as we use the following workaround:

@Bean
public ObjectMapper objectMapper(Jackson2ObjectMapperBuilder builder) {
    ObjectMapper objectMapper = builder.build();
    objectMapper.addMixIn(Object.class, IgnoreHibernatePropertiesInJackson.class);
    return objectMapper;
}

// https://stackoverflow.com/a/44152216/1939921
@JsonIgnoreProperties({"hibernateLazyInitializer"})
private static class IgnoreHibernatePropertiesInJackson {
}

This issue seems very similar to https://jira.spring.io/browse/DATAREST-1442, although

With FetchType.EAGER serialization does not fail but resulting JSON does contain unnecessary "_embedded" section.

seems not to apply here

---

Reference URL: https://github.com/jvanheesch/spring-data-rest-bytebuddyinterceptor

1 votes, 2 watchers

[spring-projects-issues]

Oliver Drotbohm commented

We cannot control the serialization of object instances produced by Hibernate but AFAIR, the Jackson Hibernate module should make work proxies OOTB. Are you using that?

[spring-projects-issues]

jvanheesch commented

I was not.
I added the com.fasterxml.jackson.datatype:jackson-datatype-hibernate5 dependency and did nothing else (e.g. I did not register the Hibernate5Module myself), and I no longer have errors!
However, I stumbled upon another issue.
curl [http://localhost:8080/books/1] now returns

{
  "title": "Spring Data REST Reference Guide",
  "author": {
    "content": {
      "name": "Jon Brisbin"
    }
  },
  "_links": {
    "self": {
      "href": "http://localhost:8080/books/1"
    },
    "book": {
      "href": "http://localhost:8080/books/1"
    }
  }
}

If I change the FetchType from LAZY to EAGER, I get:

{
  "title": "Spring Data REST Reference Guide",
  "author": {
    "name": "Jon Brisbin"
  },
  "_links": {
    "self": {
      "href": "http://localhost:8080/books/1"
    },
    "book": {
      "href": "http://localhost:8080/books/1"
    }
  }
}

Notice that in the first case, author has a content property (EntityModel), while in the second case, it doesn't (i.e. the content property is unwrapped).
I assume this behavior should not depend on the FetchType

[spring-projects-issues]

Oliver Drotbohm commented

Are you able to produce a minimal reproducing project so that I can investigate?

[spring-projects-issues]

jvanheesch commented

I had made such project, but apparently I forgot to link it.
Reference URL is now updated (https://github.com/jvanheesch/spring-data-rest-bytebuddyinterceptor).
If you GET [http://localhost:8080/books/1], you should see the following:

{
  "title": "Spring Data REST Reference Guide",
  "author": {
    "content": {
      "name": "Jon Brisbin"
    }
  },
  "_links": {
    "self": {
      "href": "http://localhost:8080/books/1"
    },
    "book": {
      "href": "http://localhost:8080/books/1"
    }
  }
}

If in class Book you change the FetchType of author from FetchType.LAZY to EAGER and restart the application, GET [http://localhost:8080/books/1] will return following:

{
  "title": "Spring Data REST Reference Guide",
  "author": {
    "name": "Jon Brisbin"
  },
  "_links": {
    "self": {
      "href": "http://localhost:8080/books/1"
    },
    "book": {
      "href": "http://localhost:8080/books/1"
    }
  }
}

[spring-projects-issues]

Oliver Drotbohm commented

Unfortunately this seems to be an issue in Jackson's Hibernate 5 module. Whether to unwrap or not involves a lookup in the target serializer which the HibernateProxySerializer doesn't answer accordingly. I'Ve commented on the other ticket to see whether we can get this fixed.

In general I think the fundamental problem shouldn't be that ubiquitous as entities internal to the aggregate (i.e. references to other non-aggregate) should be mapped to eagerly load by default. There's simply no point in delaying the loading as Jackson will need them to render them anyway

[spring-projects-issues]

jvanheesch commented

Thank you for proposing a fix for that issue!

There's simply no point in delaying the loading as Jackson will need them to render them anyway.
When using projections, Jackson may not need the author property.
In that case, FetchType.LAZY avoids the join of Book with the Author table

[spring-projects-issues]

jvanheesch commented

The bug in Jackson's Hibernate 5 module has been fixed (com.fasterxml.jackson.datatype:jackson-datatype-hibernate5:jar:2.11.2).
This fix is included when upgrading to spring-boot-starter-parent:2.3.3.RELEASE, so this issue may be closed

[spring-projects-issues]

Oliver Drotbohm commented

Resolving as suggested as it's fixed in an upstream project