Simplify projection of a single field when using Panache with Hibernate

With the current version of Panache with Hibernate, if we want to project a field from an entity, we need to do this:

import io.quarkus.runtime.annotations.RegisterForReflection;

@RegisterForReflection 
public class PersonName {
    public final String name; 

    public PersonName(String name){ 
        this.name = name;
    }
}

// only 'name' will be loaded from the database
PanacheQuery<PersonName> query = Person.find("status", Status.Alive).project(PersonName.class);

It seems a lot of work for returning a single field.

It would be nice ot have a way to specify a field:

PanacheQuery<String> query = Person.find("status", Status.Alive).project("name");

or, maybe,

PanacheQuery<String> query = Person.find("status", Status.Alive).project(Person.attribute("name", String.class));

For comparison, using HIbernate one can do:

session.createQuery("select name from Fruit ...")

This issue applies to both Panache with Hibernate ORM and Panache with Hibernate Reactive

Maybe we should also consider what happens when a user run a query like this:

List<String> distinctNames = Person.find("select distinct p.name from Person p").???.list();

One idea:

List<String> names = Person.distinct().find("status", Status.Alive).project("name", String.class).list()

WORKAROUND: I haven’t tested but it seems that this will work:

List<String> names = Person
    .find("select distinct name from Person where ...")
    .project(String.class)
    .list()

[FroMage]

No, the signature of .find is

<T extends PanacheEntityBase> PanacheQuery<T> find(String query,  ... )

So it needs to be an entity class

That signature was a mistake, I’ve wanted to drop that constraint for a long time. We should really drop it.

[DavideD]

To be fair Hibernate already handle all these scenarios.

If one select a single field, it will return a list of the type of the field. Otherwise, it will return a List<Object[]>.

I think we should do the same:

List<String> names = Person.findAll().project("name").list();
List<Object[]> custom = Person.findAll().project("name", "status").list();

People can then handle the list the way they prefer.