JPA：单向多对一和级联删除

Question

Say I have a unidirectional @ManyToOne relationship like the following:

@Entity
public class Parent implements Serializable {

    @Id
    @GeneratedValue
    private long id;
}

@Entity
public class Child implements Serializable {

    @Id
    @GeneratedValue
    private long id;

    @ManyToOne
    @JoinColumn
    private Parent parent;  
}

If I have a parent P and children C ₁ ...C _n referencing back to P, is there a clean and pretty way in JPA to automatically remove the children C ₁ ...C _n when P is removed (ie entityManager.remove(P) )?

What I'm looking for is a functionality similar to ON DELETE CASCADE in SQL.

Answer 1

If you are using hibernate as your JPA provider you can use the annotation @OnDelete . This annotation will add to the relation the trigger ON DELETE CASCADE , which delegates the deletion of the children to the database.

Example:

public class Parent {
   
        @Id
        private long id;

}


public class Child {
        
        @Id
        private long id;
  
        @ManyToOne
        @OnDelete(action = OnDeleteAction.CASCADE)
        private Parent parent;
}
     

With this solution a unidirectional relationship from the child to the parent is enough to automatically remove all children. This solution does not need any listeners etc. Also a JPQL query like DELETE FROM Parent WHERE id = 1 will remove the children.

Answer 2

Relationships in JPA are always unidirectional, unless you associate the parent with the child in both directions. Cascading REMOVE operations from the parent to the child will require a relation from the parent to the child (not just the opposite).

You'll therefore need to do this:

• Either, change the unidirectional @ManyToOne relationship to a bi-directional @ManyToOne , or a unidirectional @OneToMany . You can then cascade REMOVE operations so that EntityManager.remove will remove the parent and the children. You can also specify orphanRemoval as true, to delete any orphaned children when the child entity in the parent collection is set to null, ie remove the child when it is not present in any parent's collection.
• Or, specify the foreign key constraint in the child table as ON DELETE CASCADE . You'll need to invoke EntityManager.clear() after calling EntityManager.remove(parent) as the persistence context needs to be refreshed - the child entities are not supposed to exist in the persistence context after they've been deleted in the database.

Answer 3

Create a bi-directional relationship, like this:

@Entity
public class Parent implements Serializable {

    @Id
    @GeneratedValue
    private long id;

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

Answer 4

I have seen in unidirectional @ManytoOne, delete don't work as expected. When parent is deleted, ideally child should also be deleted, but only parent is deleted and child is NOT deleted and is left as orphan

Technology used are Spring Boot/Spring Data JPA/Hibernate

Sprint Boot : 2.1.2.RELEASE

Spring Data JPA/Hibernate is used to delete row .eg

parentRepository.delete(parent)

ParentRepository extends standard CRUD repository as shown below ParentRepository extends CrudRepository<T, ID>

Following are my entity class

@Entity(name = “child”)
public class Child  {

    @Id
    @GeneratedValue
    private long id;

    @ManyToOne( fetch = FetchType.LAZY, optional = false)
    @JoinColumn(name = “parent_id", nullable = false)
    @OnDelete(action = OnDeleteAction.CASCADE)
    private Parent parent;
}

@Entity(name = “parent”)
public class Parent {

    @Id
    @GeneratedValue
    private long id;

    @Column(nullable = false, length = 50)
    private String firstName;


}

Answer 5

用这种方式只删除一侧

    @ManyToOne(cascade=CascadeType.PERSIST, fetch = FetchType.LAZY)
//  @JoinColumn(name = "qid")
    @JoinColumn(name = "qid", referencedColumnName = "qid", foreignKey = @ForeignKey(name = "qid"), nullable = false)
    // @JsonIgnore
    @JsonBackReference
    private QueueGroup queueGroup;

Answer 6

@Cascade(org.hibernate.annotations.CascadeType.DELETE_ORPHAN)

Given annotation worked for me. Can have a try

For Example :-

     public class Parent{
            @Id
            @GeneratedValue(strategy=GenerationType.AUTO)
            @Column(name="cct_id")
            private Integer cct_id;
            @OneToMany(cascade=CascadeType.REMOVE, fetch=FetchType.EAGER,mappedBy="clinicalCareTeam", orphanRemoval=true)
            @Cascade(org.hibernate.annotations.CascadeType.DELETE_ORPHAN)
            private List<Child> childs;
        }
            public class Child{
            @ManyToOne(fetch=FetchType.EAGER)
            @JoinColumn(name="cct_id")
            private Parent parent;
    }

Answer 7

您不需要使用双向关联而不是代码，只需将 CascaType.Remove 作为属性添加到 ManyToOne 注释，然后使用 @OnDelete(action = OnDeleteAction.CASCADE)，它对我来说很好用。