Java JPA获取最后一个持久实体问题的ID

Question

我已阅读此处的文章，但无法解决我的问题 How to get Id of last persisted entity using JPA

无法获取学生最后一个自增主键

这是来自 Servlet 类

if (operation.equalsIgnoreCase("Add")) {
            student.setName(name);
            student.setAddress(address);


            int last = studentDAO.addStudent(student);
            request.setAttribute("last", last);
            request.setAttribute("student", student);

        }

这是来自 session bean:

public int addStudent(Student student) {
        em.persist(student);

        em.flush();

        System.out.println(student.getStudentID());
        return student.getStudentID();
    }

我只是使用 sout 来测试，看看我是否获得了 ID，但每次我添加 学生 时它总是输出 0。我无法获取最后生成的id。任何帮助将不胜感激。谢谢!

编辑:我的学生类(class):

封装型号；

导入javax.persistence.*;

@Entity
@Table
@NamedQueries({@NamedQuery(name="Student.getAll", query="Select e from Student e")})
public class Student {
    @Id
    @Column
    private int studentID;
    @Column
    private String name;
    @Column
    private String address;

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getStudentID() {
        return studentID;
    }

    public void setStudentID(int studentID) {
        this.studentID = studentID;
    }

    public Student(int studentID, String name, String address) {
        this.studentID = studentID;
        this.name = name;
        this.address = address;
    }
    public Student(){}
}

--解决了! Peter回复，谢谢!

Answer 1

您的数据库中的 ID 会增加吗？也许您忘记了 id 定义上方的 @GenerateValue 注释。检查这个:http://www.objectdb.com/java/jpa/entity/generated