java - 在 hibernate 中保存

我正在关注gontuseries中的教程。因此，我有这段代码可在数据库中保留两条记录。

我的测试班：

public class Test {

    private HibernateUtility util;
    private Session session;
    private Transaction tx;

    public Test() {
        util = HibernateUtility.getInstance();
        session = util.getSessionFactory().openSession();
        tx = session.beginTransaction();
    }

    public void simpleSaving() {

        List<StudentInfo> students = new ArrayList<StudentInfo>();

        StudentInfo student = new StudentInfo();
        student.setRollNo(1);
        student.setName("Jo");
        student.setBirthdate(new Date());

        StudentInfo student2 = new StudentInfo();
        student.setRollNo(2);
        student.setName("JC");
        student.setBirthdate(new Date());

        students.add(student);
        students.add(student2);

        for(StudentInfo s : students) {
            session.save(s);
        }

        tx.commit();
        session.close();
        util.getSessionFactory().close();

    }
}

这是我的POJO：

@Entity
@Table(name="student_info")
public class StudentInfo implements Serializable{
    @Id
    private int rollNo;

    @Column(name="name")
    private String name;

    @Temporal(TemporalType.DATE)
    @Column(name="birth_date")
    private Date birthdate;

    public StudentInfo(){};

    public StudentInfo(int rollNo, String name) {
        this.rollNo = rollNo;
        this.name = name;
    }

    public int getRollNo() {
        return rollNo;
    }

    public void setRollNo(int rollNo) {
        this.rollNo = rollNo;
    }

    public String getName() {
        return name;
    }

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

    public Date getBirthdate() {
        return birthdate;
    }

    public void setBirthdate(Date birthdate) {
        this.birthdate = birthdate;
    }

}

但是它给我一个错误：


  造成原因：
  com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException：
  列“ birth_date”不能为空


为什么呢？非常感谢你！

最佳答案

您实例化student2，然后再次在student上设置所有属性，这意味着student2的属性永远不会被设置并且不会使数据库约束失效。设置student2的属性，就可以了。

    StudentInfo student = new StudentInfo();
    student.setRollNo(1);
    student.setName("Jo");
    student.setBirthdate(new Date());

    StudentInfo student2 = new StudentInfo();
    student.setRollNo(2);  # this isn't student2
    student.setName("JC"); # this isn't student2
    student.setBirthdate(new Date()); # this isn't student2