如何在Hibernate中从XML生成主键?
问题描述:
我有一个用户等级:如何在Hibernate中从XML生成主键?
public class User{
private Long userId;
}
而且我在XML中使用这样的:
<id name="userId" type="long" unsaved-value="null">
<column name="USER_ID" not-null="true" />
<generator class="native" />
</id>
但是,当我试图保存用户对象不分配的用户id到我的对象得到以下错误:
Caused by: java.sql.SQLException: Field 'USER_ID' doesn't have a default value
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:957)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3878)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3814)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2478)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2625)
at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2551)
at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:1861)
at com.mysql.jdbc.PreparedStatement.executeUpdateInternal(PreparedStatement.java:2073)
at com.mysql.jdbc.PreparedStatement.executeUpdateInternal(PreparedStatement.java:2009)
at com.mysql.jdbc.PreparedStatement.executeLargeUpdate(PreparedStatement.java:5094)
at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:1994)
at org.hibernate.engine.jdbc.internal.ResultSetReturnImpl.executeUpdate(ResultSetReturnImpl.java:208)
... 22 more
我想让Hibernate为我生成id。我在这里错过了什么?
答
您需要设置autoincrement
为USER_ID列
ALTER TABLE users ADD USER_ID INT UNSIGNED NOT NULL AUTO_INCREMENT;
native
指令意味着你的数据库获取生成ID的责任。因为你没有设置在数据库端生成ID的策略,所以你得到了异常java.sql.SQLException: Field 'USER_ID' doesn't have a default value
。