使用JPA CRUD存储库查找儿童实体的数量

Question

我一直在使用JPA CRUD存储库缺省方法，例如find，findAll，delete等，以用于我所有的数据库操作。

现在我有两个实体：

@Entity 
public class Parent implements Serializable { 

    @Id 
    @GeneratedValue 
    private long id; 

    @OneToMany(mappedBy = "parent", cascade = CascadeType.REMOVE) 
    private Set<Child> children; 
} 

@Entity 
public class Child implements Serializable { 

    @Id 
    @GeneratedValue 
    private long id; 

    @ManyToOne 
    @JoinColumn 
    private Parent parent; 
} 

有没有办法为我创造ParentRepository的新方法，它可以让我找回基于父的ID父母的所有儿童的计数？

所以我ParentRepository里面，我可以创建一个看起来像这样的方法：

int findAllChildrenCount(Long parentID); 

Answer 1

尝试这些：

public interface ParentRepo extends JpaRepository<Parent, Long> { 

    Long countByChildren_Parent(Parent parent); 

    @Query("select count(c) from Parent p join p.children c where p = ?1") 
    Long countChildrenByParent(Parent parent); 

    Long countByChildren_ParentId(Long id); 

    @Query("select count(c) from Parent p join p.children c where p.id = ?1") 
    Long countChildrenByParentId(Long id); 
} 

public interface ChildRepo extends JpaRepository<Child, Long> { 

    Long countByParent(Parent parent); 

    @Query("select count(c) from Child c where c.parent = ?1") 
    Long countChildrenByParent(Parent parent); 

    Long countByParentId(Long id); 

    @Query("select count(c) from Child c where c.parent.id = ?1") 
    Long countChildrenByParentId(Long id); 
} 

Answer 2

@Query("select size(u.children) from Parent u where u.id=:parentID") 
int findAllChildrenCount(@Param("parentID")Long parentID);