Question

我需要一些帮助我对hibernate有新功能我已经使用内连接加入了三个表，这些表都有一对一映射我在列表中得到结果但是，如何迭代该列表。我试过使用迭代器，但没有任何帮助，请在这里帮助我是代码片段。

@Entity
public class Laptop {
@Id
private int lid;
private String lname;
//getters and setter

@Entity
public class Validity{

@Id
private int lid;
private String validitydate;
//getters and setter
@Entity
public class Student {

@Id
private int lid;
private int rollno;
private String name;
private int marks;


@OneToOne(cascade = CascadeType.ALL)
@JoinColumn(name="lid")
private Laptop laptop;

@OneToOne(cascade=CascadeType.ALL)
@JoinColumn(name="lid")
private Validity validity;
//getters and setters

查询我正在解雇

  String hql = "Select s from Student s inner join s.laptop left join 
   s.validity where s.lid = 1 and s.marks = 45";


    Query query = session.createQuery(hql);

    List<Object[]> list = query.list();

    Iterator it = list.iterator();
    Object[] obj = list.toArray();
    while(it.hasNext())
    {
        Object ob = (Object)it.next();
        Student s = (Student)ob;
        System.out.println("Student id is "+s.getLid());
        Laptop l = (Laptop)ob; // gives me error here cannot cast laptop to 
        student
        System.out.println("laptop id is "+l.getLid());
        System.out.println("laptop name is "+l.getLname());

    }

Answer 1

您的查询是

Select s from Student s where ...

因此它选择了学生的实例。

结果是List<Student>，而不是List<Object[]>。

使用正确的类型，并使用类型化查询：

Query<Student> query = session.createQuery(hql, Student.class);
List<Student> list = query.list();
for (Student student : list) {
    ...
}

Answer 2

    Iterator it = list.iterator();
    Object[] obj = list.toArray();
    while(it.hasNext())
    {
        Object ob = (Object)it.next();
        Student s = (Student)ob;
        System.out.println("Student id is "+s.getLid());
        Laptop l = s.getLaptop();
        System.out.println("laptop id is "+l.getLid());
        System.out.println("laptop name is "+l.getLname());
        Validity v = s.getValidity();
        System.out.println("Validity id is "+v.getLid());
        System.out.println("Validity Date is "+v.getValiditydate());

    }

内部加入hql以及如何迭代

2 个答案: