Question

我正在努力解决hibernate问题，因为几小时后在任何网站上找不到任何帮助。我已经阅读了几十个教程，尝试了所有内容，但我总是遇到类强制转换异常或编译错误。

我在数据库的这个特定部分（mysql innodb）中的模式是Plane和Steward。他们分享了Many2Many的关系。

使用Hibernate代码生成和Hibernate工具我生成了所有POJO类和映射文件（包括FlightHasStewardId和FlightHasSteward - ＆gt; Mapped Composite ID）。

我现在想要在100号航班上宣读所有管家！

注意：阅读其他实体是有效的，只有M2M读取结果在ClassCastEX中。

这是我的输入：

FlightHasSteward的映射：

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<!-- Generated Jan 1, 2014 1:52:14 PM by Hibernate Tools 4.0.0 -->
<hibernate-mapping>
    <class name="FlightHasSteward" table="Flight_has_Steward" catalog="project3flight">
        <composite-id name="id" class="FlightHasStewardId">
            <key-property name="flightIdflight" type="int">
                <column name="Flight_idflight" />
            </key-property>
            <key-property name="stewardIdsteward" type="int">
                <column name="Steward_idsteward" />
            </key-property>
        </composite-id>
    </class>
</hibernate-mapping>

FlightHasSteward.java：

// default package
// Generated Jan 1, 2014 1:52:14 PM by Hibernate Tools 4.0.0

/**
 * FlightHasSteward generated by hbm2java
 */
public class FlightHasSteward implements java.io.Serializable {

    private FlightHasStewardId id;

    public FlightHasSteward() {
    }

    public FlightHasSteward(FlightHasStewardId id) {
        this.id = id;
    }

    public FlightHasStewardId getId() {
        return this.id;
    }

    public void setId(FlightHasStewardId id) {
        this.id = id;
    }

}

FlightHasStewardId.java：

// default package
// Generated Jan 1, 2014 1:52:14 PM by Hibernate Tools 4.0.0

/**
 * FlightHasStewardId generated by hbm2java
 */
public class FlightHasStewardId implements java.io.Serializable {

    private int flightIdflight;
    private int stewardIdsteward;

    public FlightHasStewardId() {
    }

    public FlightHasStewardId(int flightIdflight, int stewardIdsteward) {
        this.flightIdflight = flightIdflight;
        this.stewardIdsteward = stewardIdsteward;
    }

    public int getFlightIdflight() {
        return this.flightIdflight;
    }

    public void setFlightIdflight(int flightIdflight) {
        this.flightIdflight = flightIdflight;
    }

    public int getStewardIdsteward() {
        return this.stewardIdsteward;
    }

    public void setStewardIdsteward(int stewardIdsteward) {
        this.stewardIdsteward = stewardIdsteward;
    }

    public boolean equals(Object other) {
        if ((this == other))
            return true;
        if ((other == null))
            return false;
        if (!(other instanceof FlightHasStewardId))
            return false;
        FlightHasStewardId castOther = (FlightHasStewardId) other;

        return (this.getFlightIdflight() == castOther.getFlightIdflight())
                && (this.getStewardIdsteward() == castOther.getStewardIdsteward());
    }

    public int hashCode() {
        int result = 17;

        result = 37 * result + this.getFlightIdflight();
        result = 37 * result + this.getStewardIdsteward();
        return result;
    }

}

Reader.java（我的课程要读）：

/* Method to READ all the stewards on specific flight */
public void getStewards(int flightid) {
    Session session = factory.openSession();
    Transaction tx = null;
    try {
        tx = session.beginTransaction();

        // Query query = session
        // .createQuery(" FROM FlightHasSteward as FHS LEFT JOIN FHS.Flight AS F ON F.idFlight = FHS.Flight_idFlight RIGHT JOIN FHS.Steward AS S ON S.idSteward = FHS.Steward_idSteward where FHS.Flight_idFlight = :code");
        Query query = session.createQuery(" FROM FlightHasSteward where Flight_idFlight = :code");
        query.setParameter("code", flightid);
        List<FlightHasStewardId> result = query.list();

        final List<FlightHasStewardId> res = (List<FlightHasStewardId>) query.list();
        for (final FlightHasStewardId hall_calendar : res) {
            System.out.println(hall_calendar.getStewardIdsteward());
        }
        tx.commit();
    } catch (HibernateException e) {
        if (tx != null)
            tx.rollback();
        e.printStackTrace();
    } finally {
        session.close();
    }

}

令人不安的输出：

Exception in thread "main" java.lang.ClassCastException: FlightHasSteward cannot be cast to FlightHasStewardId
    at Reader.getStewards(Reader.java:97)
    at Manager.main(Manager.java:24)

感谢您对本案的任何帮助，谢谢大家。

Answer 1

您是从FlightHasSteward中选择的，因此结果List将包含这些类型而不是FlightHasStewardId

Query query = session.createQuery(" FROM FlightHasSteward where Flight_idFlight = :code");
query.setParameter("code", flightid);
List<FlightHasSteward> result = query.list();
final List<FlightHasSteward> res = (List<FlightHasSteward>) query.list();
for (final FlightHasSteward steward : res) {
        System.out.println(steward.getId().getStewardIdsteward());
}

Hibernate映射复合键ManyToMany导致ClassCastException

1 个答案: