13.4. DML(数据操作语言)风格的操作(DML-style operations)

As already discussed, automatic and transparent object/relational mapping is concerned with the management of object state. This implies that the object state is available in memory, hence manipulating (using the SQL Data Manipulation Language (DML) statements: INSERT, UPDATE, DELETE) data directly in the database will not affect in-memory state. However, Hibernate provides methods for bulk SQL-style DML statement execution which are performed through the Hibernate Query Language (HQL).

UPDATE 和 DELETE语句的语法为: ( UPDATE | DELETE ) FROM? EntityName (WHERE where_conditions)? 有几点说明:

举个例子,使用Query.executeUpdate()方法执行一个HQL UPDATE语句(: (方法命名是来源于JDBC's PreparedStatement.executeUpdate()):

Session session = sessionFactory.openSession();
Transaction tx = session.beginTransaction();

String hqlUpdate = "update Customer c set c.name = :newName where c.name = :oldName";
// or String hqlUpdate = "update Customer set name = :newName where name = :oldName";
int updatedEntities = s.createQuery( hqlUpdate )
        .setString( "newName", newName )
        .setString( "oldName", oldName )
        .executeUpdate();
tx.commit();
session.close();

HQL UPDATE statements, by default do not effect the version or the timestamp property values for the affected entities; this is in keeping with the EJB3 specification. However, you can force Hibernate to properly reset the version or timestamp property values through the use of a versioned update. This is achieved by adding the VERSIONED keyword after the UPDATE keyword.

Session session = sessionFactory.openSession();
Transaction tx = session.beginTransaction();
String hqlVersionedUpdate = "update versioned Customer set name = :newName where name = :oldName";
int updatedEntities = s.createQuery( hqlUpdate )
        .setString( "newName", newName )
        .setString( "oldName", oldName )
        .executeUpdate();
tx.commit();
session.close();

注意,自定义的版本类型(org.hibernate.usertype.UserVersionType)不允许和update versioned语句联用。

执行一个HQL DELETE,同样使用 Query.executeUpdate() 方法:

Session session = sessionFactory.openSession();
Transaction tx = session.beginTransaction();

String hqlDelete = "delete Customer c where c.name = :oldName";
// or String hqlDelete = "delete Customer where name = :oldName";
int deletedEntities = s.createQuery( hqlDelete )
        .setString( "oldName", oldName )
        .executeUpdate();
tx.commit();
session.close();

由Query.executeUpdate()方法返回的整型值表明了受此操作影响的记录数量。 注意这个数值可能与数据库中被(最后一条SQL语句)影响了的“行”数有关,也可能没有。一个大批量HQL操作可能导致多条实际的SQL语句被执行, 举个例子,对joined-subclass映射方式的类进行的此类操作。这个返回值代表了实际被语句影响了的记录数量。在那个joined-subclass的例子中, 对一个子类的删除实际上可能不仅仅会删除子类映射到的表而且会影响“根”表,还有可能影响与之有继承关系的joined-subclass映射方式的子类的表。

INSERT语句的伪码是: INSERT INTO EntityName properties_list select_statement. 要注意的是:

执行HQL INSERT语句的例子如下:

Session session = sessionFactory.openSession();
Transaction tx = session.beginTransaction();

String hqlInsert = "insert into DelinquentAccount (id, name) select c.id, c.name from Customer c where ...";
int createdEntities = s.createQuery( hqlInsert )
        .executeUpdate();
tx.commit();
session.close();