Question

我有两个表父母和孩子之间有@oneTomany关系。以下是我的表结构。

表格结构

CREATE TABLE `parent` (
  `id_parent` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(255) DEFAULT NULL,
  PRIMARY KEY (`id_parent`)
)

CREATE TABLE `child` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(255) DEFAULT NULL,
  `parent_id` int(3) NOT NULL,
  PRIMARY KEY (`id`),
  KEY `fk_parent_child` (`group_id`),
  CONSTRAINT `fk_parent_child` FOREIGN KEY (`parent_id`) REFERENCES `parent` (`id_parent`)
)

我为此创建了实体类，如下所示

家长班。

@Entity
@Table(name = "parent")
public class Parent {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id_parent")
    private int id;

    @Column(name = "name")
    private String name;

    @OneToMany(mappedBy = "defaultchild", fetch = FetchType.EAGER)
    @Cascade({ CascadeType.SAVE_UPDATE, CascadeType.MERGE })
    private Set<Child> childs;

    //setter and getters.
}

儿童班。

@Entity
@Table (name = "child")
public class Report {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column (name = "id")
    private int id;
    @Column (name = "name")
    private String name;

    @ManyToOne
    @Cascade({org.hibernate.annotations.CascadeType.SAVE_UPDATE,org.hibernate.annotations.CascadeType.MERGE})
    @JoinColumn(name="parent_id")
    private Parent defaultchild;    

    @ManyToMany(fetch = FetchType.LAZY)
    @JoinTable(name = "group",joinColumns={@JoinColumn(name="fk_child_id")},inverseJoinColumns={@JoinColumn(name="fk_group_id")})
    private Set<XXX> groups = new HashSet<XXX>(0);
    //Setter and Getter methods
}

服务类

public UIGroup getParentByName(String name) {
    return DAO.getParentByName(name);
}

@Transactional(readOnly = false, propagation = Propagation.REQUIRED)
public boolean updateParent(Parent parent) {
    return DAO.updateParent(parent);
}


@Transactional(readOnly = false, propagation = Propagation.REQUIRED)
public boolean deleteParent(Parent parent) {
    return DAO.deleteParent(parent);
}

DAO Class。

public UIGroup getParentByName(String name) {
    Query query;
    Parent parent = null;
    try {
        String queryString = " from Parent where name = :name";
        query = sessionFactory.getCurrentSession().createQuery(queryString);
        query.setParameter("name", name);
        uiGroup = (Parent) query.uniqueResult();
    } catch (Exception e) {
        logger.error(e);
    }
    return parent;
}

public boolean updateParent(Parent parent) {
    boolean result = true;
    Session session = null;
    Transaction tx = null;
    try {
        session = sessionFactory.getCurrentSession();
        tx = session.beginTransaction();
        session.merge(parent);
        tx.commit();
        session.flush();
    } catch (HibernateException e) {
        result = false;
        logger.error(e);
    }// end of try-catch block.
    return result;
}


public boolean deleteParent(Parent parent) {
    boolean result = true;
    Session session = null;
    try {
        session = sessionFactory.getCurrentSession();
        session.delete(parent);
    } catch (HibernateException e) {
        result = false;
        logger.error( + e);
    }
    return result;
}

但是当我尝试调用以下代码时

Parent otherParent = Service.getParentByName("Other");
Parent parent = Service.getParentByName("XYZ");
//here I am assigning childs assign to XYX parent to other Parent
Set<Child> childs = new TreeSet<Child>(Child.COMPARE_BY_ID);
childs.addAll(otherParent.getchildes());
childs.addAll(parent.getchilde());
otherParent.setChilds(childs);
Service.updateParent(otherParent);
Service.deleteParent(parent);

我收到了以下错误。

错误的

java.sql.BatchUpdateException: Cannot delete or update a parent row: a foreign key constraint fails (`database`.`child`, CONSTRAINT `fk_parent_child` FOREIGN KEY (`parent_id`) REFERENCES `child` (`id_parent`))

这意味着我的更新代码无法正常运行以下是Service.updateParent（otherParent）语句的日志

SELECT parent0_.id_parent AS id1_135_1_, parent0_.name AS name135_1_, childs1_.parent_id AS parent4_3_, childs1_.id AS id3_, childs1_.id AS id143_0_, childs1_.child_name AS child2_143_0_, childs1_.is_sea_child AS is3_143_0_, childs1_.parent_id AS parent4_143_0_ 
FROM ui_parent parent0_ 
LEFT OUTER JOIN child childs1_ ON parent0_.id_ui_parent=childs1_.parent_id 
WHERE parent0_.id_parent=1

请帮帮我，我不知道这段代码出了什么问题提前谢谢。

Answer 1

我可能会写一个DAO方法moveAllChildren（String srcName，String dstName），如下所示：

public class ParentDAO {
    @PersistenceContext
    private EntityManager em;

    public Parent findParentByName(name) {
      TypedQuery<Parent> q = em.createQuery("select p from Parent where p.name = :name", Parent.class);
      return q.setParameter("name", name).getSingleResult();
    }

    public void moveAllChildren(String srcName, String dstName) {
      Parent src = findParentByName(srcName);
      Parent dst = findParentByName(dstName);
      Set<Child> children = new HashSet<Child>();
      for (Child c: src.getChildren()) {
        children.add(c);
      }
      src.getChildren().removeAll(children);
      dst.getChildren().addAll(children);
    }
}

一般情况下，使用Cascading时，明确添加和删除子项是一种良好做法，而不是说dst.setChildren（allChildren），以便让JPA有机会管理Relation的两端。如果你不这样做，你可能会认为孩子仍然认为src是他们的父母，然后你可能会看到你的数据库违反约束。

此外，尝试让JPA尽可能多地管理您的实体内容是一个好主意。所以我宁愿没有应用程序调用服务调用DAO来检索父项只移动他们的子项然后调用相同的服务调用相同的DAO将这些更改合并到数据库中。你最好将它作为DAO级别的低级操作实现，然后添加一个调用它来处理@Transaction的服务。

Answer 2

如果您没有选择限制@Cascade类型的具体原因，则可以选择切换为全部。

  @Cascade({ CascadeType.ALL})

甚至只是

  @OneToMany(cascade=CascadeType.ALL, mappedBy="defaultchild")

编辑：你有几次错误拼写'父母'，修复它也不会有什么坏处。

Answer 3

您尝试删除parent但可能仍有childs。在删除之前尝试清空childs集合：

for(Child child : parent.getChilds()){
    child.setParent(null);
}
parent.getChilds().clear();
Service.deleteParent(parent);

如果parent仍有参考，则无法删除Child。

Answer 4

最终我在wallenborn的帮助下得到了解决方案并且链接

JPA not saving foreign key to @OneToMany relation

以下是我在课堂上所做的更改。

实体类。

@Entity
@Table(name = "parent")
public class Parent {

    .....   

    @OneToMany(cascade = CascadeType.PERSIST,mappedBy = "defaultchild", fetch = FetchType.EAGER)
    private Set<Child> childs;

    //setter and getters.
}

@Entity
@Table (name = "child")
public class Child {

    ....

    @ManyToOne
    @JoinColumn(name="parent_id")
    private Child defaultchild; 

    //Setter and Getter methods
}

我已经更改了wallenborn建议的服务和DAO课程，如下所示

服务类。

@Transactional(readOnly = false, propagation = Propagation.REQUIRED)
public void moveAllChildren(String srcName, String dstName) {
    DAO.moveAllChildren(srcName, dstName);
}

DAO课程

public Parent findParentByName(name) {
      TypedQuery<Parent> q = em.createQuery("select p from Parent where p.name = :name", Parent.class);
      return q.setParameter("name", name).getSingleResult();
    }

    public void moveAllChildren(String srcName, String dstName) {
      Parent src = findParentByName(srcName);
      Parent dst = findParentByName(dstName);
      Set<Child> children = new HashSet<Child>();
      for (Child c: src.getChildren()) {
        children.add(c);
    }
    src.getChildren().removeAll(children);
    dst.getChildren().addAll(children);
}

Hibernate在更新父对象时不更新子对象

4 个答案: