hibernate - 在 Hibernate 中防止 select 查询时插入

Question

我是 Hibernate 新手。我有一个问题，当我尝试运行选择查询时说

"from Foo where Foo.some_id=2"

(使用 Hibernate 模板)然后 Hibernate 还会尝试将记录插入到与 Foo 表具有一对二一关联的表“Foo2”中

bean

class Foo{
int id;
....
Foo2 foo2;
}

Foo.hbm.xml

...
<one-to-one name="foo2" class="Foo2" property-ref="foo"
  constrained="false" cascade="save-update"></one-to-one>
...

bean Foo2

Class Foo2{
...
private int foo;
...
}

Foo2.hbm.xml

...
<property name="foo" column="foo_id"/>
...

用法

 DetachedCriteria criteria = createDetachedCriteria();
  criteria.add(Restrictions.eq("some_id", value));
  return getHibernateTemplate().findByCriteria(criteria);

    public List<SnsUser> getAllSnsUsersByProperty(String prop, Object val){
            String query = "from SnsUser su where su." + prop + " =:" + prop;
            return executeQuery(query, new String[]{prop}, new Object[]{val});
    }

    public static void main(String[] args) { //WORKING
    String query = "from SnsUser su where su.blessUserId=1";
    Session session = Utility.getSessionFactory().openSession();
    List l = new SnsUserDaoImpl().getQRes(query);
    System.out.println(l);
    session.close();
    }
public List<E> executeQuery(String queryString, String []param, Object [] val){
//NOT WORKING
        return getHibernateTemplate().findByNamedParam(queryString, param, val);
    }   

这就是我得到的......

Hibernate: select * from bless_aggregation.sns_user this_ left outer join bless_aggregation.sns_authenticator snsauthent2_ on this_.sns_uid=snsauthent2_.sns_uid 
where this_.bless_uid=?
Hibernate: select * from bless_aggregation.bless_user blessuser0_ where blessuser0_.bless_uid=?
Hibernate: select * from bless_aggregation.sns_user snsuser0_ left outer join bless_aggregation.sns_authenticator snsauthent1_ on 
snsuser0_.sns_uid=snsauthent1_.sns_uid where snsuser0_.bless_uid=?

Hibernate: insert into bless_aggregation.sns_authenticator (key, value, sns_uid) values (?, ?, ?)
1079 [main] WARN org.hibernate.util.JDBCExceptionReporter - SQL Error: 1064, SQLState: 42000
1079 [main] ERROR org.hibernate.util.JDBCExceptionReporter - 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 'key, value, sns_uid) values (null, null, 1)' at line 1

Answer 1

我的猜测是，您在 session 中有挂起的更改(一些 Foo2 实例等待插入)，并且默认情况下，Hibernate 在运行查询之前刷新 session 以提供非过时的结果。文档的以下部分对此进行了解释:

10.10. Flushing the Session

Sometimes the Session will execute the SQL statements needed to synchronize the JDBC connection's state with the state of objects held in memory. This process, called flush, occurs by default at the following points:

• before some query executions
• from org.hibernate.Transaction.commit()
• from Session.flush()

The SQL statements are issued in the following order:

1. all entity insertions in the same order the corresponding objects were saved using Session.save()
2. all entity updates
3. all collection deletions
4. all collection element deletions, updates and insertions
5. all collection insertions
6. all entity deletions in the same order the corresponding objects were deleted using Session.delete()

An exception is that objects using native ID generation are inserted when they are saved.

Except when you explicitly flush(), there are absolutely no guarantees about when the Session executes the JDBC calls, only the order in which they are executed. However, Hibernate does guarantee that the Query.list(..) will never return stale or incorrect data.

It is possible to change the default behavior so that flush occurs less frequently. The FlushMode class defines three different modes: only flush at commit time when the Hibernate Transaction API is used, flush automatically using the explained routine, or never flush unless flush() is called explicitly. The last mode is useful for long running units of work, where a Session is kept open and disconnected for a long time (see Section 11.3.2, “Extended session and automatic versioning”).

sess = sf.openSession();
Transaction tx = sess.beginTransaction();
sess.setFlushMode(FlushMode.COMMIT);

// allow queries to return stale state

Cat izi = (Cat) sess.load(Cat.class, id);
izi.setName(iznizi);

// might return stale data
sess.find("from Cat as cat left outer join cat.kittens kitten");

// change to izi is not flushed!
...
tx.commit(); // flush occurs
sess.close();

During flush, an exception might occur (e.g. if a DML operation violates a constraint). Since handling exceptions involves some understanding of Hibernate's transactional behavior, we discuss it in Chapter 11, Transactions and Concurrency.

因此，正如上面所解释的和代码片段中所示，尝试使用FlushMode.COMMIT。

请注意，如果您使用 identity 生成器，这将无济于事，Hibernate 将在 save 时间写入数据库。

另请注意，FlushMode 只是 Session 的提示，其行为并未得到严格保证。