Allow dynamic EntityGraph in repositories

[JordanDurieux]

At the moment you have to write X times the same JPQL query if you want to have X different entitygraphs.

It would be great to enable dynamic EntityGraph with a special parameter in the repositories interfaces.

My suggestion would be to have a new special parameter (like Pageable and Sort) using JpaEntityGraph.
When this parameter is present, it would add the hint to the EntityManager with the entity graph to use.

Add a special parameter (handling the parameter index and so on) :

package org.springframework.data.repository.query;

public class Parameter {

	static final List<Class<?>> TYPES = Arrays.asList(Pageable.class, Sort.class, JpaEntityGraph.class);

[...]
}

In AbstractJpaQuery, add the hint to the query thanks to JpaParametersParameterAccessor :

    protected Query createQuery(JpaParametersParameterAccessor parameters) {
        return applyLockMode(applyEntityGraphConfiguration(applyHints(doCreateQuery(parameters), method), method, parameters), method);
    }

    private Query applyEntityGraphConfiguration(Query query, JpaQueryMethod method, JpaParametersParameterAccessor accessor) {

        if (method.getEntityGraph() != null && accessor.getJpaEntityGraph() != null) {
            throw new IllegalStateException("Cannot have EntityGraph annotation and JpaEntityGraph parameter at the same time!");
        }

        JpaEntityGraph entityGraph = method.getEntityGraph();

        if (entityGraph == null) {
            entityGraph = accessor.getJpaEntityGraph();
        }

        if (entityGraph != null) {
            Map<String, Object> hints = Jpa21Utils.tryGetFetchGraphHints(em, entityGraph , getQueryMethod().getEntityInformation().getJavaType());

            for (Map.Entry<String, Object> hint : hints.entrySet()) {
                query.setHint(hint.getKey(), hint.getValue());
            }
        }
        else if (entityGraphName != null) {
            // Maybe here use Jpa21Utils to make additional checks
            query.setHint(hint.getKey(), em.getEntityGraph(entityGraphName.getValue()));
        }

        return query;
    }

The usage in repositories would be :

public interface MyRepository extends JpaRepository<MyEntity, MyID> {

    @Query("...some jpql query...")
    List<MyEntity> findByMyProp(String myProp, JpaEntityGraph jpaEntityGraph);

}

Then we can use different entity graphs depending on the caller's context :

// Assuming we have a new JpaEntityGraph constructor with name only (defaulting the type to FETCH like the annotation)
myRepository.findByMyProp("something", new JpaEntityGraph("myentity-with-some-nodes"));
myRepository.findByMyProp("something", new JpaEntityGraph("myentity-with-other-nodes"));

[schauder]

Duplicate of #951