Question

我尝试第一次映射关系。我找到了很多方法。

有两个类： - 项目（家长） - 申请（儿童）

因此，一个项目可以有多个应用程序，但一个应用程序只属于一个项目..

我按如下方式构建它们：

Project.java

 import javax.persistence.CascadeType;
    import javax.persistence.Entity;
    import javax.persistence.GeneratedValue;
    import javax.persistence.GenerationType;
    import javax.persistence.Id;
    import javax.persistence.JoinColumn;
    import javax.persistence.OneToMany;

    @Entity
    public class Project {

     @Id
     @GeneratedValue(strategy = GenerationType.IDENTITY)
     private int id;
        @OneToMany(cascade = CascadeType.ALL)
        @JoinColumn(name = "project_id", nullable=false)
        @org.hibernate.annotations.IndexColumn(name = "project_index")
        List<Application> applications = new ArrayList<Application>();

        [get and set methods...]
        }

Application.java

import javax.persistence.Entity;
    import javax.persistence.GeneratedValue;
    import javax.persistence.GenerationType;
    import javax.persistence.Id;
    import javax.persistence.JoinColumn;
    import javax.persistence.ManyToOne;

    @Entity
    public class Application {

         @Id
         @GeneratedValue(strategy = GenerationType.IDENTITY)
         private int id;

            @ManyToOne
            @JoinColumn(name = "project_id", updatable = false, insertable = false, nullable=false)
            private Project project;

        [get and set methods...]
     }

...但不幸的是，我得到了一个我无法处理的例外：

javax.servlet.ServletException: org.hibernate.PropertyValueException: not-null property references a null or transient value: ....common.entities.Application._applicationsBackref
 javax.faces.webapp.FacesServlet.service(FacesServlet.java:321)
 org.apache.shiro.web.servlet.AbstractShiroFilter.executeChain(AbstractShiroFilter.java:359)
 org.apache.shiro.web.servlet.AbstractShiroFilter$1.call(AbstractShiroFilter.java:275)
 org.apache.shiro.subject.support.SubjectCallable.doCall(SubjectCallable.java:90)
 org.apache.shiro.subject.support.SubjectCallable.call(SubjectCallable.java:83)
 org.apache.shiro.subject.support.DelegatingSubject.execute(DelegatingSubject.java:343)
 org.apache.shiro.web.servlet.AbstractShiroFilter.doFilterInternal(AbstractShiroFilter.java:272)
 org.apache.shiro.web.servlet.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:83)

root cause

javax.faces.el.EvaluationException: org.hibernate.PropertyValueException: not-null property references a null or transient value: ....common.entities.Application._applicationsBackref
 javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:98)
 com.sun.faces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:98)
 javax.faces.component.UICommand.broadcast(UICommand.java:311)
 javax.faces.component.UIViewRoot.broadcastEvents(UIViewRoot.java:781)
 javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:1246)
 com.sun.faces.lifecycle.InvokeApplicationPhase.execute(InvokeApplicationPhase.java:77)
 com.sun.faces.lifecycle.Phase.doPhase(Phase.java:97)
 com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:114)
 javax.faces.webapp.FacesServlet.service(FacesServlet.java:308)
 org.apache.shiro.web.servlet.AbstractShiroFilter.executeChain(AbstractShiroFilter.java:359)
 org.apache.shiro.web.servlet.AbstractShiroFilter$1.call(AbstractShiroFilter.java:275)
 org.apache.shiro.subject.support.SubjectCallable.doCall(SubjectCallable.java:90)
 org.apache.shiro.subject.support.SubjectCallable.call(SubjectCallable.java:83)
 org.apache.shiro.subject.support.DelegatingSubject.execute(DelegatingSubject.java:343)
 org.apache.shiro.web.servlet.AbstractShiroFilter.doFilterInternal(AbstractShiroFilter.java:272)
 org.apache.shiro.web.servlet.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:83)

root cause

org.hibernate.PropertyValueException: not-null property references a null or transient value: ....common.entities.Application._applicationsBackref
 org.hibernate.engine.Nullability.checkNullability(Nullability.java:95)
 org.hibernate.event.def.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:313)
 org.hibernate.event.def.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:204)
 org.hibernate.event.def.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:130)
 org.hibernate.event.def.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:210)
 org.hibernate.event.def.DefaultSaveEventListener.saveWithGeneratedOrRequestedId(DefaultSaveEventListener.java:56)
 org.hibernate.event.def.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:195)
 org.hibernate.event.def.DefaultSaveEventListener.performSaveOrUpdate(DefaultSaveEventListener.java:50)
 org.hibernate.event.def.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:93)

我的错误在哪里？我的意思是什么都没有。仅在项目方面

当我在拥有方移除@JoinColumn时会发生异常：

java.sql.SQLException: Field 'project_id' doesn't have a default value

谢谢Pascal

Answer 1

您的映射中有几件事需要解决。

您的关联是双向的，您需要使用“One”一侧的mappedBy属性（或者您将得到的是两个单向关联）来定义“拥有”拥有关系的字段一方（持有外键的一方，即一对多的多方）。
@JoinColumn注释应仅在拥有方定义，而不是双方定义。
如果您使用的是兼容JPA 2.0的Hibernate版本（即Hibernate 3.5+），则更喜欢Hibernate特定@OrderColumn的标准@IndexColumn注释
我不确定为什么您将@JoinColumn定义为updatable = false, insertable = false, nullable=false完全只读，这听起来不合适。

所以你的映射成为（假设你正在使用JPA 2.0）：

@Entity
public class Project {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;

    @OneToMany(cascade = CascadeType.ALL, mappedBy="project")
    @OrderColumn(name = "project_index")
    List<Application> applications = new ArrayList<Application>();

    // getters, setters
}

并且

@Entity
public class Application {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;

    @ManyToOne
    @JoinColumn(name = "project_id")
    private Project project;

    // getters, setters
 }

由于你的关联是双向的，所以在创建对象图时不要忘记设置链接的两边：

Project p = new Project();
Application a = new Application();
a.setProject(p);
p.getApplications().add(a);
em.persist(p);

但我实际上建议您在实体中创建链接管理方法以设置链接的两面，例如

@Entity
public class Project {
    ...
    public void addToApplications(Application app) {
        this.applications.add(app);
        app.setProject(this);
    }
    ...
}

资源

Hibernate核心文档
- 1.2.6. Working bi-directional links
JPA维基书
- Example of a OneToMany relationship and inverse ManyToOne annotations

参考

JPA 1.0规范
- 第2.1.8.2节“双向ManyToOne / OneToMany关系”
- 第9.1.24节“OneToMany注释”
- 第9.1.22节“ManyToOne注释”
JPA 2.0规范
- 第11.1.39节“OrderColumn注释”

Answer 2

双方都不需要

@JoinColumn注释。事实上，你应该把它放在关系的一面。

此外，您已经描述了以下内容，

@JoinColumn(name = "project_id", updatable = false, insertable = false, nullable=false)

完全没有意义。实际上，这意味着您不想更新它，既不想插入它，也不想要它为空。

此外，如果实际列的名称不是@Column，则您在Id字段上缺少id注释。

Answer 3

实体

@Table(name="Customer_v1")

@Inheritance(strategy = InheritanceType.SINGLE_TABLE)

@DiscriminatorColumn(name = "type", discriminatorType = DiscriminatorType.STRING)

public class Customer implements Serializable{                

                @Id

                @Column(name="cust_id")

                protected int custId;

 ------------------------------------------------

@Entity

@DiscriminatorValue(value = "N")

public class NewCustomer extends Customer {}

 

@Entity

@DiscriminatorValue( value="E")

public class ExistingCustomer extends Customer{}

Hibernate onetomany映射

3 个答案:

资源

参考