UNION to JPA Query

Question

Is it possible to query \"UNION\" in JPA and even \"Criteria Builder\"?

I\'m looking for examples, but so far i got no result.

Does anyone have any examples

Answer 1

There is no direct union for JPA, what I did was to build two specifications.

Specification specification = Specification.where(null);
Specification specification2 = Specification.where(null;

They belong to a single table but return different values

specification = specification.and((root, criteriaQuery, criteriaBuilder) -> criteriaBuilder.equal(criteriaBuilder.function(MONTH, Integer.class, root.get("deliveryExpirationDate")), month));
        specification2 = specification2.and((root, criteriaQuery, criteriaBuilder) -> criteriaBuilder.lessThan(criteriaBuilder.function(MONTH, Integer.class, root.get("deliveryExpirationDate")), month))
            .and((root, criteriaQuery, criteriaBuilder) -> criteriaBuilder.equal(root.get("enable"), true));

for this example it is a table of tasks that in the first specification I need the tasks of the current month enabled and disabled, and in the second specification I only need the tasks enabled of the previous months.

Specification specificationFullJoin = Specification.where(specification).or(specification2);

Esto es muy útil para que la lista de tareas devueltas tenga paginación.

taskRepository.findAll(specificationFullJoin, pageable).map(TaskResponse::new); //Here you can continue adding filters, sort or search.

It helps me a lot, I hope it is what they are looking for or that it serves them something.