如何使 JPA @query 与其中有另一个投影的投影一起工作

Question

I'm trying to get projections works on @query in JPA with joined columns as an another project as well.

Say, I have 2 entities: course and student and student can have many courses and the foreign key is on the course table:

student(id, name, email, age, grade, uuid)

course(id, name, uuid, student_id)

And I have projections like these:

public interface CourseProjection {
  UUID getUuid();
}

And,

public interface StudentProjection {
  String getName();
  String getEmail();
  Set<CourseProjection> getCourses();
}

In the entity:

public class Student {
    // other code
    @OneToMany(mappedBy = "student")
    private Set<Course> courses = new LinkedHashSet<>();
}

I need to do LIKE search on multiple columns including course uuid. I also need I also want pagination. So, in the repository, I want to do something like:

@Repository
interface StudentRepository extends JpaRepository<Student, UUID> {
  @Query(
     value = "SELECT * FROM student s LEFT JOIN courses c ON s.id = 
     c.student_id WHERE s.name LIKE %str% OR c.student_id::text LIKE %str%",
     nativeQuery = true
  )
  Page<StudentProjection> findAllByKeyword(String keyword, Pageable pageable);
}

I want the result looks like this:

[
  {
    name: John
    email: johndoe@gmail.com
    courses: [
      "course_uuid_1",
      "course_uuid_2"
    ]
  }
  {
    ...
  }
]

Any suggestions on how to achieve this?

Answer 1

Do you have try:

1. interface StudentRepository extends JpaRepository, excerptProjection = projectionName.class To hard this projection to the repository.

2. Https:domain/contextpath/students/search/findAllByKeyword?projection=projectionName To apply projection for this rest api. And you need add more configuration as below:

    @Configuration public class RepositoryConfig extends RepositoryRestConfigurerAdapter { @Override public void configureRepositoryRestConfiguration(RepositoryRestConfiguration config) { config.getProjectionConfiguration().addProjection(projectionName.class)); } }

Answer 2

When using Spring Data nested closed projections with custom queries , you need to make sure you are definitely:

1. Nesting projections
2. Explicitly declaring column aliases

I ran into the same issue, trying to figure out how to solve it. Your code would've worked totally fine if you just had done:

public interface StudentProjection {
    String getName();
    String getEmail();
    Set<CourseProjection> getCourses();
    
    interface CourseProjection {
        UUID getUuid();
    }
}

And then used your custom query like this:

@Query(nativeQuery = true,
            value = "SELECT s.name as name, s.email as email, c.uuid as uuid "
                    + "FROM student s "
                    + "LEFT JOIN courses c ON s.id = c.student_id "
                    + "WHERE s.name LIKE %str% OR c.student_id::text LIKE %str%")
Page<StudentProjection> findAllByKeyword(String keyword, Pageable pageable);

I also believe there was no need for using a native query, you could've just used HQL/JPQL instead or even Spring Data query methods .

I know this question is a bit old, but it can be helpful to other people out there.