1

这是代码:

@Entity
public class Dept {
  @Id 
  @GeneratedValue(strategy = GenerationType.AUTO)
  private Integer id;
  @OneToMany(
    mappedBy = "dept",
    cascade = CascadeType.ALL
  )
  private List<Employee> employees = new ArrayList<Employee>();
  public void addEmployee(Employee emp) {
    this.employees.add(emp);
  }
}

@Entity
public class Employee {
  @Id 
  @GeneratedValue(strategy = GenerationType.AUTO)
  private Integer id;
  @Column private Integer age;
  public Employee(Integer a) {
    this.age = a;
  }
}

然后在单元测试中我这样做(使用 OpenJPA):

// ...
Dept dept = new Dept();
dept.addEmployee(new Employee(25));
this.em.persist(dept);

OpenJPA 说:

Caused by: <openjpa-1.2.1-r752877:753278 nonfatal general error>
org.apache.openjpa.persistence.PersistenceException: Attempt to insert 
null into a non-nullable column: column: ID table: EMPLOYEE in 
statement [INSERT INTO employee (age) VALUES (?)] 
{prepstmnt 841687127 INSERT INTO employee (age) VALUES (?) 
[params=(int) 25]} [code=-10, state=23000]

为什么 ID 不是自动生成的?

4

1 回答 1

1

您的一对多关系被映射为双向(由于mappedBy),但我看不到另一面。也许这就是原因。

即使确实存在多对一,尽管它是关系的拥有方,但它并没有在您的代码中初始化,因此它指定要在数据库中反映的状态。

如果您实际上是指单向关系,则需要删除mappedBy.

于 2010-11-17T13:20:14.810 回答