Question

我一直在使用JPA CRUD存储库默认方法，例如find，findAll，delete等，用于我的所有数据库操作。

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;  
}

我有没有办法在ParentRepository中创建一个新方法，让我根据父级ID检索父级所有子级的计数？

所以在我的ParentRepository中，我可以创建一个看起来像这样的方法：

int findAllChildrenCount(Long parentID);

Answer 1

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

Answer 2

试试这些：

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);
}

使用JPA CRUD存储库查找子实体的计数

2 个答案: