How can I add a subselect to result in jpa query - jpa

Question

I have an Spring boot app with an entity Person with a list of that persons events on.
Like this.
public class Person....
private Long id;
private String name;
#ElementCollection(fetch = FetchType.EAGER)
#CollectionTable(name = "person_events", joinColumns = #JoinColumn(name = "person_id"))
private List<String> personEvents = new ArrayList<>();
Now when I select I want to select the result into a dto like this.
#Query("""
select new com.....dtos.PersonDto(p.name, p.events) from Person p
where p.name = (:name)
""")
Set<PersonDto> findPersonsByName(String name);
My repository fails because it cant generate the sql. How can I achieve this?

Answer 1

Few things you are doing can be improved like:
Instead of constructor select you can use interface projection
Set<PersonDto> findPersonsByName(String name);
Since you are doing a select on single item the result will be single object.
so please change it to
PersonDTO findPersonsByName(String name);
Please find my complete answer below:
package com.example.demo;
import lombok.Getter;
import lombok.Setter;
import lombok.ToString;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;
import org.springframework.web.bind.annotation.*;
import javax.persistence.*;
import java.util.ArrayList;
import java.util.Collection;
import java.util.List;
#RestController
#RequestMapping("/person")
public class PersonController {
private final PersonService personService;
#Autowired
public PersonController(PersonService personService) {
this.personService = personService;
}
#GetMapping
public Iterable<Person> list() {
return personService.list();
}
#PostMapping
public Person create(#RequestBody Person car) {
return personService.save(car);
}
#GetMapping(path = "/by")
public PersonDTO getPersonByName(#RequestParam(value = "name") String name) {
return personService.findPersonByName(name);
}
}
#Getter
#Setter
#ToString
#Entity
class Person {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
private Integer id;
private String name;
#ElementCollection(fetch = FetchType.EAGER)
#CollectionTable(name = "person_events", joinColumns = #JoinColumn(name = "person_id"))
private List<String> personEvents = new ArrayList<>();
}
#Service
class PersonService {
private final PersonRepository personRepository;
#Autowired
PersonService(PersonRepository personRepository) {
this.personRepository = personRepository;
}
#Transactional
public Person save(Person person) {
return personRepository.save(person);
}
#Transactional(readOnly = true)
public Iterable<Person> list() {
return personRepository.findAll();
}
#Transactional(readOnly = true)
public PersonDTO findPersonByName(String name) {
return personRepository.findPersonsByName(name);
}
}
interface PersonDTO {
String getName();
Collection<String> getPersonEvents();
}
#Repository
interface PersonRepository extends JpaRepository<Person, Integer> {
PersonDTO findPersonsByName(String name);
}