Question

我们在项目中经常使用Criteria进行动态查询生成。我真的很喜欢查询的表达方式。问题是我们发现这个特定的查询无法使用基于clientId的索引，所以我们需要更改它。这是工作的非索引查询：

public List<EventInstance> getEventInstances(Date from, Date to, Integer clientId) {
    Session session = this.getSession();

    Criteria criteria = session.createCriteria(EventInstance.class);

    if(clientId != null){

        criteria.add(Restrictions.disjunction()
            .add(Restrictions.eq("clientId", clientId))
            .add(Restrictions.eq("team1ClientId", clientId))
            .add(Restrictions.eq("team2ClientId", clientId))
            );
    }

    if(from != null){
        criteria.add(Restrictions.ge("startTime", from));
    }

    if(to != null){
        criteria.add(Restrictions.le("startTime", to));
    }

    @SuppressWarnings("unchecked")
    List<EventInstance> events = criteria.list();

    this.releaseSession(session);
    return events;
}

此查询只能使用startTime索引，并且无法使用任何clientId的索引。我发现以下形式的查询有效地使用了我们的索引，我想用条件创建此查询：

select * from ( select * from eventInstance where (clientId = 8 or team1ClientId = 8 or team2ClientId = 8) ) evtalias where evtalias.startTime < now()

我已经能够使用以下代码在WHERE子句中进行子选择：

public List<EventInstance> getEventInstances(Date from, Date to, Integer clientId){
    Session session = this.getSession();

    DetachedCriteria subSelectClient = DetachedCriteria.forClass(EventInstance.class);
    if(clientId != null){
        subSelectClient.add(Restrictions.disjunction()
            .add(Restrictions.eq("clientId", clientId))
            .add(Restrictions.eq("team1ClientId", clientId))
            .add(Restrictions.eq("team2ClientId", clientId))
            )
            .setProjection(Property.forName("id"));
    }


    Criteria criteria = session.createCriteria(EventInstance.class);

    if(clientId != null){
        criteria.add(Property.forName("id").in(subSelectClient));
    }

    if(from != null){
        criteria.add(Restrictions.ge("startTime", from));
    }

    if(to != null){
        criteria.add(Restrictions.le("startTime", to));
    }

    @SuppressWarnings("unchecked")
    List<EventInstance> events = criteria.list();

    this.releaseSession(session);
    return events;
}

这会生成如下查询：

select * from eventInstance this_ where this_.id in (select this_.id as y0_ from eventInstance this_ where (this_.clientId=8 or this_.team1ClientId=8 or this_.team2ClientId=8)) and this_.startTime<=now();

使用索引比使用原始查询更糟糕，并且不会在FROM中进行子选择。

所以我的问题是，我可以在标准中执行此操作，还是我坚持使用HQL甚至本机SQL。或者，如果你知道如何创建一个可以解决我的问题的索引，但我从mysql文档中理解的是，这是不可能的。

以下是我想要创建的目标查询的解释输出：

mysql> explain select * from ( select * from eventInstance where (clientId = 8 or     team1ClientId = 8 or team2ClientId = 8) ) evtalias where evtalias.startTime < now();
+----+-------------+---------------+-------------+-------------------------------+-----    ------------------+---------+------+------+------------------------------------------------    --------------+
| id | select_type | table         | type        | possible_keys                 | key                    | key_len | ref  | rows | Extra                                                        |
+----+-------------+---------------+-------------+-------------------------------+-----------------------+---------+------+------+--------------------------------------------------------------+
|  1 | PRIMARY     | <derived2>    | ALL         | NULL                          | NULL                   | NULL    | NULL |  288 | Using where                                                  |
|  2 | DERIVED     | eventInstance | index_merge | eijoin2,ei_client,team2,team1 | ei_client,team1,team2 | 5,5,5   | NULL |  300 | Using union(ei_client,team1,team2); Using where; Using index |
+----+-------------+---------------+-------------+-------------------------------+-----------------------+---------+------+------+--------------------------------------------------------------+
2 rows in set (0.00 sec)

这是hibernate标准子查询的解释：

+----+--------------------+-------+-----------------+---------------------------------------+---------+---------+------+-------+-------------+
| id | select_type        | table | type            | possible_keys                         | key     | key_len | ref  | rows  | Extra       |
+----+--------------------+-------+-----------------+---------------------------------------+---------+---------+------+-------+-------------+
|  1 | PRIMARY            | this_ | ALL             | ei3                                   | NULL    | NULL    | NULL | 49434 | Using where |
|  2 | DEPENDENT SUBQUERY | this_ | unique_subquery | PRIMARY,eijoin2,ei_client,team2,team1 | PRIMARY | 4       | func |     1 | Using where |
+----+--------------------+-------+-----------------+---------------------------------------+---------+---------+------+-------+-------------+
2 rows in set (0.00 sec)

Answer 1

据我所知，Criteria和HQL都不能在from子句中生成带子查询的查询，因此您必须使用本机SQL。

我可以使用Hibernate的Criteria在from子句中生成子查询吗？

1 个答案: