从 Spring 数据 JPA 查询方法返回自定义集合

Question

I would like my custom query method to return a specific Guava collection type ( ImmutableSet in my example).

Example:

public interface MyRepository extends CrudRepository<User,UserId> {

  @Query("SELECT DISTINCT u FROM User u WHERE... ORDER BY ...")
  ImmutableSet<User> findByxxxx();

}

When I try it, I get:

Failed to convert from type [java.util.ArrayList<?>] to type [com.google.common.collect.ImmutableSet<?>]
...
Caused by: java.lang.IllegalArgumentException: Could not instantiate Collection type: com.google.common.collect.ImmutableSet

The documentation does not explicitly list the Guava collection types, so I am not sure if it is impossible without a new release, or if there is some configuration that is possible to make it work.

How can I instruct Spring Data JPA to use that type?

Answer 1

Spring data doesn't support collections from any third-party libraries and probably never do...

CrudRepository exposes an Iterable to you and if you want to materialize to custom collection it's up to you to do that.

By the way If you want your repository returns custom collection types you can decorate the spring data repository with yours. Like this

interface JpaUserRepository extends CrudRepository<User,UserId> {

  @Query("SELECT DISTINCT u FROM User u WHERE... ORDER BY ...")
  Iterable<User> findByxxxx();

}
public class MyRepository {

   private final JpaUserRepository jpaUserRepository;

   @Autowired
   public MyRepository(final JpaUserRepository jpaUserRepository) {
     this.jpaUserRepository = jpaUserRepository;
   } 

   public ImmutableSet<User> findByxxxx() {
     return ImmutableSet.copyOf(jpaUserRepository.findByXXX());
   }

}