Support hibernate-enhance-maven-plugin plugin

[hurelhuyag]

Compile-time class enhancement has advantages. When we use it hibernate does not need to create new classes at runtime. But this module is not working with the hibernate-enhance-maven-plugin. Because this enhancer plugin adds proxy to getters and Jackson serializer calls getter before detecting property state. We should find a way to detect property that is lazily loaded before invoking the getter method.

I have created a minimal project for demonstrating this behaviour.

https://github.com/hurelhuyag/demo-jackson-hibernate5-mininal

[cowtowncoder]

This sounds useful! I don't have time or personal itch to work on this but I hope someone has -- and I will be happy to help improvement(s) merged in once ready, and to help with Jackson side aspects (I am not very Hibernaty savvy).

[hurelhuyag]

@cowtowncoder I looked at the source code of this project. Then I found out It didn't use Hibernate's provided Hibernate.isInitialized, Hibernate.isPropertyInitialized methods. Is there a specific reason not to use those methods?

[hurelhuyag]

I can create PR. But I need to understand how Jackson works.
Can you guide me here?

[hurelhuyag]

I just created a maven profile to test with hibernate-enhance-maven-plugin
#167

[cowtowncoder]

@hurelhuyag I did not write this extension module and never used Hibernate so unfortunately I do not know the logic. If I had to guess, I'd suggest that perhaps this method was not available in some (earlier) versions of Hibernate.

[hurelhuyag]

After days of digging. I found a fairly simple solution. Unfortunately, This solution can't be applied by Module.

    @JsonFilter("lazyPropertyFilter")
    public interface LazyPropertyFilterMixin {}

    @Bean
    Jackson2ObjectMapperBuilderCustomizer jackson2ObjectMapperBuilderCustomizer() {
        return builder -> builder
            .mixIn(ManagedEntity.class, LazyPropertyFilterMixin.class)
            .mixIn(HibernateProxy.class, LazyPropertyFilterMixin.class)
            .filters(new SimpleFilterProvider(Map.of("lazyPropertyFilter", new LazyPropertyFilter())));
    }

[cowtowncoder]

Modules can actually do such registration (although with bit of casting). But requirement to overwrite FilterProvider is bit of a blocker; modules should not do that as it prevents users from providing their own filters.

One possibility would be to add a separate helper module to be registered along with main module. Or helper class.

One request: could you include LazyPropertyFilter implementation along with code sample (I know it's probably part of the test project).

[hurelhuyag]

My Latest LazyPropertyFilter implementation:

public class LazyPropertyFilter implements PropertyFilter {

    @Override
    public void serializeAsField(Object pojo, JsonGenerator gen, SerializerProvider prov, PropertyWriter writer) throws Exception {
        var initialized = isPropertyInitialized((BeanPropertyWriter) writer, pojo);
        if (initialized) {
            writer.serializeAsField(pojo, gen, prov);
        } else if (!gen.canOmitFields()) { // since 2.3
            writer.serializeAsOmittedField(pojo, gen, prov);
        }
    }

    @Override
    public void serializeAsElement(Object elementValue, JsonGenerator gen, SerializerProvider prov, PropertyWriter writer) {
        throw new RuntimeException("LazyPropertyFilter.serializeAsElement() currently unsupported");
    }

    @SuppressWarnings("deprecation")
    @Override
    public void depositSchemaProperty(PropertyWriter writer, ObjectNode propertiesNode, SerializerProvider provider) throws JsonMappingException {
        writer.depositSchemaProperty(propertiesNode, provider);
    }

    @Override
    public void depositSchemaProperty(PropertyWriter writer, JsonObjectFormatVisitor objectVisitor, SerializerProvider provider) throws JsonMappingException {
        writer.depositSchemaProperty(objectVisitor, provider);
    }

    public static boolean isPropertyInitialized(BeanPropertyWriter prop, Object bean) throws Exception {
        return Hibernate.isPropertyInitialized(bean, prop.getName())
            && isInitialized(prop, bean, ManyToOne.class, ManyToOne::fetch)
            && isInitialized(prop, bean, ElementCollection.class, ElementCollection::fetch)
            && isInitialized(prop, bean, OneToMany.class, OneToMany::fetch)
            && isInitialized(prop, bean, Basic.class, Basic::fetch);
    }

    public static <A extends Annotation> boolean isInitialized(
        BeanPropertyWriter prop, Object bean, Class<A> type, Function<A, FetchType> fetch) throws Exception {
        var ann = prop.getAnnotation(type);
        if (ann == null) {
            return true;
        }
        var fetchType = fetch.apply(ann);
        if (fetchType == FetchType.EAGER) {
            return true;
        }
        var value = prop.get(bean);
        return Hibernate.isInitialized(value);
    }
}