不能只更新父，休眠

Question

嗨：我是hibernate的新手，我正在尝试加载已经存在于DB中的订单，更改字段然后更新订单但是我遇到了以下异常：“org.hibernate.exception .LockTimeoutException：无法执行语句“。 （必须说我不改变订单的行）

public static void closeOrder(Integer idOrder) {
  Session session = HibernateUtil.getSessionFactory().openSession();
  Transaction tx = null;

  try
  {         
    tx = session.beginTransaction();

    Order order = (Order) session.load(Order.class, idOrder);
    order.setDate (new SimpleDateFormat("yyyy-MM-dd").format(new Date()));

    session.flush();

    tx.commit();
  }
  catch(Exception e)
  {
    if(tx != null)
    {
      tx.rollback();
    }
    e.printStackTrace();
  }
  finally
  {
    session.close();
  }
}

Hibernate映射： Order.hbm.xml

<hibernate-mapping package="com.Pojos">
    <class name="Order" table="Order">
        <id name="idOrder" type="int" column="idOrder">
            <generator class="org.hibernate.id.enhanced.SequenceStyleGenerator"> 
                <param name="sequence_name">Order_SEQ</param>
                <param name="initial_value">1</param>
                <param name="increment_size">1</param> 
                <param name="value_column">CurrentValue</param> 
                <param name="optimizer">hilo</param>
            </generator>
        </id>
        <property name="date"/>
        <many-to-one name="client" column="idClient" class="Clients"/>
        <list name="orderLines" table="OrderLines">
            <key column="idOrder"/>
            <index column="idx"/>
            <one-to-many class="OrderLines"/>
        </list>
    </class>
</hibernate-mapping>

OrderLines.hbm.xml

<hibernate-mapping package="com.Pojos">
    <class name="OrderLines" table="OrderLines">
        <id name="idOrderLine" type="int" column="idOrderLine">
            <generator class="increment"/>
        </id>
        <many-to-one name="order" column="idOrder" not-null="true"/>
    </class>
</hibernate-mapping>

注意：当我创建一个新订单时，添加一些行并保存它我没有问题。

我做错了什么？