3

我有两张表，父母和孩子之间有@oneTomany 关系。以下是我的表结构。

表结构 

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

父类。

@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
}

服务等级

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 类。

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;
}

但是当我试图调用以下代码时

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);

我收到以下错误。

错误

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工作以下是 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

请帮助我，我不知道这段代码出了什么问题，谢谢。

4

4 回答 4

3

我可能只会写一个 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);
    }
}

一般来说，在使用 Cascading 时，显式添加和删除子项是很好的做法，而不是说 dst.setChildren(allChildren)，以便让 JPA 有机会管理 Relation 的双方。如果您不这样做，您可能会冒着孩子仍然认为 src 是他们的父母的风险，然后您可能会从您的数据库中看到违反约束的情况。

此外，尝试让 JPA 管理尽可能多的实体内容是一个好主意。所以我宁愿不让应用程序调用服务调用DAO来检索父母只是为了移动他们的孩子，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。您最好将其实现为 DAO 级别的低级别操作，然后添加一个服务来调用它来处理 @Transaction。

于 2013-03-08T15:55:47.743 回答
1

如果没有特定原因选择限制@Cascade类型，则可以选择切换到 ALL。

  @Cascade({ CascadeType.ALL})

甚至只是

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

编辑：你已经拼错了几次“父母”，修复它也不会有什么坏处。

于 2013-03-07T13:05:08.653 回答
0

您正在尝试删除parent，但它childs可能仍然存在。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);

parent如果 aChild仍然有引用，则不能删除。

于 2013-03-08T12:14:32.890 回答
0

最后我在wallenborn和以下链接的帮助下得到了解决方案

JPA 未将外键保存到 @OneToMany 关系

这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
}

我已将 wallenborn 建议的服务和 DAO 类更改如下

服务类。

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

DAO 类

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);
}
于 2013-03-12T07:33:43.330 回答