JPA select Query返回具有@ManyToone映射的实体

Question

我是一个初学者，学习JPA，为了练习，我在这个问题上工作，我有两个实体班Person和Gym。

Person有：-id（自动生成）-name-age-gym（多对一映射）

@Entity
public class Gym {
    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    private int gym_id;

    @NotNull
    private String name;

    @NotNull
    private String city;

    @NotNull
    @Max(5)
    private double rating;

    @NotNull
    private double fee;

    @OneToMany(mappedBy="gym", 
                cascade= {CascadeType.MERGE, CascadeType.PERSIST,
                        CascadeType.REFRESH}, fetch=FetchType.EAGER)
    @JsonManagedReference
    private List<Person> personList;

    public Gym() {
        super();
    }

    public Gym(int gym_id, @NotNull String name, @NotNull double rating, @NotNull double fee, List<Person> personList,
            @NotNull String city) {
        super();
        this.gym_id = gym_id;
        this.name = name;
        this.rating = rating;
        this.fee = fee;
        this.personList = personList;
        this.city = city;
    }
// getters and setters

@Entity
public class Person {
    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    private int id;

    @NotNull
    private String name;

    @NotNull
    private int age;

    @ManyToOne (cascade={CascadeType.MERGE, CascadeType.PERSIST,
        CascadeType.REFRESH, CascadeType.DETACH})
    @JoinColumn
    @JsonBackReference
    private Gym gym;

    public Person() {
        super();
    }

    public Person(int id, @NotNull String name, @NotNull int age, Gym gym) {
        super();
        this.id = id;
        this.name = name;
        this.age = age;
        this.gym = gym;
    }
// getters and setters

public interface PersonRepository extends JpaRepository<Person, Integer>{

@Query("select p from Person p join fetch p.gym where p.age<=(:age)")
List<Person> filterByAge(@Param("age") int age);
}

在我的服务课上，这就是我正在做的

List<Person> filteredPersonList = personRepository.filterByAge(age);
System.out.println(filteredPersonList); // prints empty

Answer 1

如果将存储库更改为此，则不需要构造查询，并且可以工作。

public interface PersonRepository extends JpaRepository<Person, Integer>{

     List<Person> findByAgeLessThanEqual(int age);

}