如何查询具有多对多关系的实体？

Question

I have 3 entities that are in relationship. The following is a simplified example of my classes:

@Entity
public class Action {}

@Entity
public class Instance {

    @ManyToMany
    private Set<Action> actions;

    @ManyToMany
    private Set<CadSystem> cadSystems;

}

@Entity
public class CadSystem {}

How can I query for all Instance s that belong to a specific Action and CadSystem ? For example I would like to do the following in a JpaRepository :

public interface InstanceRepository extends JpaRepository<Instance, Long> {

    List<Instance> findByActionAndCadSystem(Action action, CadSystem cadSystem);

}

But this is not possible because Instance has no fields named action and cadSystem . I think the following would work:

public interface InstanceRepository extends JpaRepository<Instance, Long> {

    List<Instance> findByActionsAndCadSystems(Set<Action> actions, Set<CadSystem> cadSystems);

}

But in this case I would always have to create a new Set with only one element.

Answer 1

Use a query. Also, note that since the associations are many-to-many, this query might return several actions:

select i from Instance i
join i.actions action
join i.cadSystems cadSystem
where action = :action
and cadSystem = :cadSystem