避免在 Spring 数据 JPA 中获取 @ManyToOne 属性

Question

I have three entities as below. I'm using Lombok based getters and setters:

@Getter
@Setter
@EqualsAndHashCode(callSuper = true, exclude = { "cClasses"})
class AClass {
   // some properties
   @OneToMany(mappedBy = "aClass", orphanRemoval = true)
   private List<CClass> cClasses;
}

class BClass {
  // some properties
}

@Getter
@Setter
@EqualsAndHashCode(callSuper = true, exclude = { "aClass", "bClass"})
class CClass {
  // other properties
  // this is bidirectional
  @ManyToOne(cascade = CascadeType.ALL, fetch = FetchType.LAZY)
  @JoinColumn(name = "A_ID", referencedColumnName = "A_ID")
  private AClass aClass;

  // this is unidirectional
  @ManyToOne(cascade = CascadeType.ALL, fetch = FetchType.LAZY)
  @JoinColumn(name = "B_ID", referencedColumnName = "B_ID")
  private BClass bClass;
}

And by JPA repository class looks like as below:

@Repository
public interface CClassRepository extends JpaRepository<CClass, Long> {
  List<CClass> findByBClassBidIn(List<Long> ids);
}

The output is coming as expected but the performance is very poor. I can see in logs that select queries for all AClass is also getting executed. How can I avoid the calls to @ManyToOne property aClass.

I tried using @JsonManagedReference and @JsonIgnore on aClass property of CClass. But still it is fetching those records when I'm calling repository method. Please suggest how to solve this problem.

Answer 1

It's better to invert the relationship, so ClassB can know about ClassC

class BClass {
  @OneTOMany(...)
  private CClass cClass;
}

@Repository
public interface BClassRepository extends JpaRepository<BClass, Long> {

  @Query("select ClassB.cClass where ClassB.id is in `ids`") // might be wrong syntax
  List<CClass> findCclassesByBClassIdIn(List<Long> ids);
}

Answer 2

它只查询一次数据库，即从所有者一侧查询数据库，即带有@JoinColumn 注释的一侧。