java - 在 Hibernate 的@Formula 中使用 NATURAL JOIN

Question

我在使用 @Formula 的 Hibernate 中使用 NATURAL JOIN 时遇到问题。

我有三个表:

CREATE TABLE IF NOT EXISTS `tz_points_logs` (
  `points_log_id` bigint(20) NOT NULL,
  `points_to_uid` bigint(20) NOT NULL,
  `points_get_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
  `points_rule_id` int(4) NOT NULL,
  `points_meta` text NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE IF NOT EXISTS `tz_points_rules` (
  `points_rule_id` int(4) NOT NULL,
  `points_rule_credits` int(4) NOT NULL,
  `points_rule_title` varchar(32) NOT NULL,
  `points_rule_description` text NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE IF NOT EXISTS `tz_users` (
  `uid` bigint(20) NOT NULL,
  `username` varchar(16) NOT NULL,
  `password` varchar(32) NOT NULL,
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

在 Hibernate 中，存在三种映射模型:User、PointsLog 和 PointsRule。

现在，User 模型中有一个@Formal 字段:

@Entity
@Table(name = "tz_users")
public class User implements Serializable {
    // Getters and Setters

    @Id
    @GeneratedValue
    @Column(name = "uid")
    private long uid;

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

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

    @OneToMany(targetEntity = PointsLog.class, 
                fetch = FetchType.LAZY, mappedBy = "user")
    private List<PointsLog> pointsLogs = new ArrayList<PointsLog>();

    @Formula(value = "(SELECT COUNT(*) FROM tz_points_logs pl NATURAL JOIN tz_points_rules WHERE pl.points_to_uid=uid)")
    private long credit;
}

获取用户的信用时出现错误:

com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use 
near 'user0_.NATURAL JOIN tz_points_rules WHERE pl.points_to_uid=user0_.uid) as formul' at line 1
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:408)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:377)
    at com.mysql.jdbc.Util.getInstance(Util.java:360)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:978)
    ...
    at java.lang.Thread.run(Thread.java:745)

Hibernate 似乎无法识别@Formula 中的NATURAL JOIN。 有没有其他方法可以实现这个功能？

顺便说一句，下面的语句工作正常。

@Formula(value = "(SELECT COUNT(*) FROM tz_points_logs pl WHERE pl.points_to_uid=uid)")

非常感谢。

Answer 1

在 this answer 中讨论了类似的问题.这里的重点是 - Hibernate 将 NATURAL 关键字视为属性/列名。解决方法应该是 - 在方言中将 NATURAL 注册为 keyword。

例如:

// extend the correct dialect ... in this case MySql
// but simply extend the currently used dialect
public class CustomMySQLDialect extends MySQL5InnoDBDialect
{
    public CustomMySQLDialect()
    {
        super();
        registerKeyword("NATURAL");
    }
}

接下来将 Hibernate 配置为使用此 CustomMySQLDialect，并且应生成 FORMULA:

// instead of this
// user0_.NATURAL JOIN

// we should get this
NATURAL JOIN