Question

我有两个jsps尝试访问此数据库例程（通过操作类）。当我没有try / catch / finally例程，没有提交事务或关闭会话时，我可以得到结果，但只是第一次。当下一个jsp尝试访问它们时，我得到nested transactions not supported因为我没有关闭会话。

当我关闭session.close()会话时，我得到session was already closed error。当我使用HibernateUtil.close()（因为我读到我应该关闭threadLocale）时，我得到LazyInitializationException: could not initialize proxy - no Session。

在第一次数据库命中后，我是否需要保存/保留列表？或者从懒惰变为急切加载？即使在阅读了它们之后，我也不完全理解它们如何应用于这个实例，并且如果我确实需要，也不知道如何指定eager加载。我已经看过这个注释用法fetch = FetchType.LAZY，但我如何使用映射标签来指定eager？

DAO交易

public List<Flights> getflights(String departure, String destination)
        {

            this.session = HibernateUtil.getSessionFactory().getCurrentSession();

            List<Flights> flist = null;

            if(session ==null){session = HibernateUtil.getSessionFactory().getCurrentSession();}
            Transaction tx = session.beginTransaction();
            try
            {
                String hql = "from Flights as f Where f.destinationsByDepartureCode = :departureCode AND f.destinationsByDestinationCode = :destinationCode";
                Query q = session.createQuery(hql);
                q.setParameter("departureCode", departure);
                q.setParameter("destinationCode", destination);
                flist = (List<Flights>) q.list();
                tx.commit();
                tx = null;
            }
            catch (Exception e)
            {
                tx.rollback();
                e.printStackTrace();
            }
            finally{
    //          session.close();
                HibernateUtil.closeSession(); // diff to above. this closes threadlocale.
            }

            return flist;
        }

航班制图

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<!-- Generated 07/05/2014 11:35:38 PM by Hibernate Tools 3.6.0 -->
<hibernate-mapping>
  <class catalog="seng3150" name="model.hibernate.Flights" table="flights">
    <id name="flightid" type="java.lang.Integer">
      <column name="flightid"/>
      <generator class="identity"/>
    </id>
    <many-to-one class="model.hibernate.Destinations" fetch="select" name="destinationsByStopOverCode">
      <column length="3" name="StopOverCode"/>
    </many-to-one>
    <many-to-one class="model.hibernate.Destinations" fetch="select" name="destinationsByDestinationCode">
      <column length="3" name="DestinationCode" not-null="true"/>
    </many-to-one>
    <many-to-one class="model.hibernate.Airlines" fetch="select" name="airlines">
      <column length="2" name="AirlineCode" not-null="true"/>
    </many-to-one>
    <many-to-one class="model.hibernate.Destinations" fetch="select" name="destinationsByDepartureCode">
      <column length="3" name="DepartureCode" not-null="true"/>
    </many-to-one>
    <many-to-one class="model.hibernate.Planetype" fetch="select" name="planetype">
      <column length="20" name="PlaneCode" not-null="true"/>
    </many-to-one>
    <property name="flightNumber" type="string">
      <column length="6" name="FlightNumber" not-null="true"/>
    </property>
    <property name="departureTime" type="timestamp">
      <column length="19" name="DepartureTime" not-null="true"/>
    </property>
    <property name="arrivalTimeStopOver" type="timestamp">
      <column length="19" name="ArrivalTimeStopOver"/>
    </property>
    <property name="departureTimeStopOver" type="timestamp">
      <column length="19" name="DepartureTimeStopOver"/>
    </property>
    <property name="arrivalTime" type="timestamp">
      <column length="19" name="ArrivalTime" not-null="true"/>
    </property>
    <property name="duration" type="int">
      <column name="Duration" not-null="true"/>
    </property>
    <property name="durationSecondLeg" type="java.lang.Integer">
      <column name="DurationSecondLeg"/>
    </property>
    <set fetch="select" inverse="true" lazy="true" name="bookingses" table="bookings">
      <key>
        <column name="flightid" not-null="true"/>
      </key>
      <one-to-many class="model.hibernate.Bookings"/>
    </set>
  </class>
</hibernate-mapping>

Answer 1

session.getCurrentSession()会自动关闭您的交易/会话。如果您查看this API，他们会说如果您致电session.openSession();你必须在finally块中手动关闭会话。

对于您使用延迟属性的问题，您必须在会话期间（即，当事务处于打开状态时/在关闭会话之前）获取延迟属性。在你的情况下调用commit（）之前。如果在执行该代码后调用惰性属性，则会出现该错误。

为了避免这个问题，我经常编写几个服务（对于同一个父对象）来加载父对象的不同惰性项并关闭会话。或者您可以将抓取类型设置为eager。

Hibernate LazyLoading没有会话

1 个答案: