Spring JPA selecting specific columns

You can use projections from Spring Data JPA (doc). In your case, create interface:

interface ProjectIdAndName{
    String getId();
    String getName();
}

and add following method to your repository

List<ProjectIdAndName> findAll();

I don't like the syntax particularly (it looks a little bit hacky...) but this is the most elegant solution I was able to find (it uses a custom JPQL query in the JPA repository class):

@Query("select new com.foo.bar.entity.Document(d.docId, d.filename) from Document d where d.filterCol = ?1")
List<Document> findDocumentsForListing(String filterValue);

Then of course, you just have to provide a constructor for Document that accepts docId & filename as constructor args.

You can set nativeQuery = true in the @Query annotation from a Repository class like this:

public static final String FIND_PROJECTS = "SELECT projectId, projectName FROM projects";

@Query(value = FIND_PROJECTS, nativeQuery = true)
public List<Object[]> findProjects();

Note that you will have to do the mapping yourself though. It's probably easier to just use the regular mapped lookup like this unless you really only need those two values:

public List<Project> findAll()

It's probably worth looking at the Spring data docs as well.

In my situation, I only need the json result, and this works for me:

public interface SchoolRepository extends JpaRepository<School,Integer> {
    @Query("select s.id, s.name from School s")
    List<Object> getSchoolIdAndName();
}

in Controller:

@Autowired
private SchoolRepository schoolRepository;

@ResponseBody
@RequestMapping("getschoolidandname.do")
public List<Object> getSchool() {
    List<Object> schools = schoolRepository.getSchoolIdAndName();
    return schools;
}

In my case i created a separate entity class without the fields that are not required (only with the fields that are required).

Map the entity to the same table. Now when all the columns are required i use the old entity, when only some columns are required, i use the lite entity.

e.g.

@Entity
@Table(name = "user")
Class User{
         @Column(name = "id", unique=true, nullable=false)
         int id;
         @Column(name = "name", nullable=false)
         String name;
         @Column(name = "address", nullable=false)
         Address address;
}

You can create something like :

@Entity
@Table(name = "user")
Class UserLite{
         @Column(name = "id", unique=true, nullable=false)
         int id;
         @Column(name = "name", nullable=false)
         String name;
}

This works when you know the columns to fetch (and this is not going to change).

won't work if you need to dynamically decide the columns.

Spring JPA selecting specific columns

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