@GeneratedValue(strategy = GenerationType.AUTO) 不像想象的那样工作 [英] @GeneratedValue(strategy = GenerationType.AUTO) not working as thought
本文介绍了@GeneratedValue(strategy = GenerationType.AUTO) 不像想象的那样工作的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
我正在尝试将一个对象持久化到数据库中.不断收到列 ID 不能接受空值错误".我的对象看起来像这样:
I'm trying to persist an object to a database. Keep getting 'Column ID cannot accept null value error'. My object looks like this:
@Entity
public class TestTable {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Integer id = 0;
@Column(nullable=false, length=256)
private String data = "";
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getData() {
return data;
}
public void setData(String data) {
this.data = data;
}
}
我的持久化功能:
public static synchronized boolean persistObject(Object obj){
boolean success = true;
EntityManager em = null;
EntityTransaction tx = null;
try{
em = getEmf().createEntityManager();
tx = em.getTransaction();
tx.begin();
em.persist(obj);
tx.commit();
} catch (Exception e){
success = false;
} finally{
try{
em.close();
} catch(Exception e){
//nothing
}
}
return success;
}
推荐答案
您可以使用 GenerationType.TABLE.这样,jpa 使用序列表进行 id 分配,您可能永远不需要生成降低可移植性的序列或自动递增值或触发器.
You may use GenerationType.TABLE. That way, jpa uses a sequence table for id assigment and you may never need to generate sequence or auto-increment values or triggers that lowers portability.
还要注意,在java中int类型默认为0,所以你也可以去掉它.
Also note that in java int type is initiated with 0 default, so you may get rid of that also.
这篇关于@GeneratedValue(strategy = GenerationType.AUTO) 不像想象的那样工作的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!
查看全文