题
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,在单元测试我这样做(OpenJPA中使用):
// ...
Dept dept = new Dept();
dept.addEmployee(new Employee(25));
this.em.persist(dept);
OpenJPA中表示:
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不是自动产生的?
解决方案
您一个一对多关系被映射为双向(由于mappedBy
),但我不能看到对方。也许这是原因。
和就算多到一边确实存在,它不是在你的代码初始化尽管它的关系的持有端,因此它指定在数据库中反映出来的状态
。如果你实际上意味着单向的关系,你需要删除mappedBy
。
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