Question

我陷入了一个有问题的项目。问题很简单，但我不知道解决方案。这是我的问题：

我有一个使用Hibernate，Employee Table映射的Employee类。

Class Employee
  int empId;
  int empName;

然后我有一个使用Hibernate，Assignment Table映射的Assignment类。对于每个员工，我在Assignment类中都有一个记录以及一个员工的主管ID。主管也在Employee类中定义。

Class Assignment
 int empId;
 int supervisorId; //empId of the Supervisor in the Employee Table.

现在，在我的动作类中，我首先生成了一个迭代器，它首先有一个Assignment Class的对象，我将在我的jsp中显示它，如下所示：

<s:iterator value="assignmentList">
   <s:property value="empId"/>
   <s:property value="supervisorId"/>
   //Now here i want to display the empName of both the Employee and Supervisor.
   //How can i pass the <s:property value="empId"/> and <s:property value="supervisorId"/> values to an action to get the Employee Class Objects so that i can display the employee names.

我认为这是一个加入两个表的简单问题，但不知道如何在struts2中实现它。请帮忙。

修改

这是我修改后的代码

员工类

   @Entity
   @Table(name="usertable")
   public class User implements java.io.Serializable{

   private int id;
  private String empName;
  private String firstName;
  private Assignment assignment;

 public Employee(){
 }

@Id
    @GeneratedValue
    @Column(name="id")
    public int getId() {
        return id;
    }
    @Column(name="empname")
    public String getEmpname() {
        return empName;
    }

    @OneToOne(fetch = FetchType.EAGER, mappedBy = "usertable", cascade = CascadeType.ALL)
    public Assignment getAssignment() {
        return assignment;
    }

    public void setAssignment(Assignment assignment) {
        this.assignment = assignment;
    }
}

作业类

@Entity
@Table(name="assignment")
public class Assignment implements java.io.Serializable{

private int id;
private Employee employee;

@Id
@GeneratedValue
@Column(name="id")
public int getId() {
    return id;
}
public void setId(int id) {
    this.id = id;
}
@OneToOne(fetch = FetchType.EAGER)
@JoinColumn(name = "id")
public Employee getEmployee() {
    return employee;
}
public void setEmployee(Employee employee) {
    this.employee = employee;
}

}

在Action类中保存方法

SessionFactory sf = HibernateUtil.getSessionFactory();
Session session = sf.openSession();
session.beginTransaction();
      Employee emp=new Employee();
  Assignment assgn =new Assignment();
  emp.setAssignment(assgn);
  assgn.setEmployee(emp);
  session.save(assgn);
  session.save(emp);

  session.getTransaction().commit();
  session.close();

我的Util类：

public class HibernateUtil {

private static final SessionFactory sessionFactory;

static {
    try {
        // Create the SessionFactory from hibernate.cfg.xml
        sessionFactory = new AnnotationConfiguration().configure()
                .buildSessionFactory();
    } catch (Throwable ex) {
        System.err.println("Initial SessionFactory creation failed." + ex);
        throw new ExceptionInInitializerError(ex);
    }
}

public static SessionFactory getSessionFactory() {
    return sessionFactory;
}

}

当我在我的动作类中运行save方法时，我遇到了这个异常：

Struts has detected an unhandled exception:

Messages:   
File:   org/hibernate/cfg/OneToOneSecondPass.java
Line number:    135

java.lang.NullPointerException
org.hibernate.cfg.OneToOneSecondPass.doSecondPass(OneToOneSecondPass.java:135)
org.hibernate.cfg.Configuration.secondPassCompile(Configuration.java:1163)
org.hibernate.cfg.AnnotationConfiguration.secondPassCompile(AnnotationConfiguration.java:296)
org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1319)
common.HibernateUtil.(HibernateUtil.java:14)
backEnd.admin.saveemployee(admin.java:137)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
java.lang.reflect.Method.invoke(Method.java:597)

现在该怎么解决？我正在使用Hibernate注释版本3.2.1。请帮忙。

Answer 1

您需要在此处配置一对一（或一对多，具体取决于您的型号）映射。由于您提到您有针对每个员工的分配记录，因此这意味着Employee bean应该具有对其相关分配bean的引用。

我假设你在hibernate中使用注释配置，所以你的Employee类中的一些小改动应该可以解决这个问题

//Injecting the assignment bean inside the employee bean    
private Assignement employeeAssignement;

//Lazy type fetching means to get the assignemnt tuple only when it is needed
@OneToOne(fetch = FetchType.LAZY, mappedBy = "Employee", cascade = CascadeType.ALL)
public Assignment getEmployeeAssignment() {
    return this.employeeAssignement;
}

public void setEmployeeAssignement(EmployeeAssignement employeeAssignement) {
    this.employeeAssignement = employeeAssignement;
}

另一个优良做法是保留一个单独的bean，用于显示与数据库映射的实体bean的用途。创建一个bean，比如EmployeeDetailBean，并指定要在JSP上显示的字段。

public class EmployeeDetailBean{
 //The fields you want to display on the JSP
 ......
 //valid getter/setter
}

在调用操作类时设置这些字段，为此bean创建getter / setter，并在调用JSP时迭代此bean，就像迭代帖子中提到的其他bean一样。

使用struts和hibernate在jsp中显示数据

1 个答案: