Java Spring 急切获取 Hibernate 子类失败

Question

我正在使用 Hibernate 3.2.5 创建 Spring Web MVC 3.1.1 应用程序。我正在Netbeans 7.2中开发，应用程序服务器是GlassFish 3.1.2。数据库是Mysql 5.5。

我的问题是子类没有预先加载@OneToMany ，而另一个类的 @OneToMany能够加载。这个问题仅在 Glassfish 上出现:当我运行具有完全相同逻辑的本地脚本时，没有问题。

相关 Hibernate 配置:

<hibernate-configuration>
  <session-factory>
    <property name="hibernate.hbm2ddl.auto">update</property>
    <mapping class="blagae.db.game.Game"/>
    <mapping class="blagae.db.game.GamePhase"/>
    <mapping class="blagae.db.game.Series"/>
    <mapping class="blagae.db.play.Play"/>
  </session-factory>
</hibernate-configuration>

基本思想是美式橄榄球比赛。一个Game包含几个GamePhases (Series、Kickoffs、Half Time、End Of Game)；一个Series包含Plays ，进一步分割。

<强> GamePhase & Game (这些工作):

@Entity
@Inheritance(strategy=InheritanceType.JOINED)
public class GamePhase implements Serializable {
  @Id
  @GeneratedValue
  private int gamePhaseID;
  @ManyToOne(fetch = FetchType.EAGER)
  private Game game;
}

@Entity
public class Game implements Serializable {
  @Id
  @GeneratedValue
  private int gameID;
  @OneToMany(cascade=CascadeType.ALL, mappedBy="game", fetch=FetchType.EAGER)
  private List<GamePhase> gamePhases = new ArrayList<GamePhase>();

  public List<GamePhase> getGamePhases() {
    return gamePhases;
  }

  public void setGamePhases(List<GamePhase> gamePhases) {
    this.gamePhases = gamePhases;
  }

  public Series getFirstGamePhase() throws Exception {
    if (gamePhases.isEmpty() || gamePhases == null) {
        throw new Exception ("List<GamePhase> error");
    }
    return gamePhases.get(0);
  }
}

<强> Series (<- GamePhase ) 和 Play :

@Entity
@Inheritance(strategy=InheritanceType.JOINED)
public class Play implements Countable, Serializable {
  @ManyToOne
  private Series series;
}

@Entity
public class Series extends GamePhase implements Countable {
  @OneToMany(cascade=CascadeType.ALL, mappedBy="series",fetch=FetchType.EAGER)
  private List<Play> plays = new ArrayList<Play>();

  public List<Play> getPlays() {
    return plays;
  }

  public void setPlays(List<Play> plays) {
    this.plays = plays;
  }

  public Play getFirstPlay() throws Exception {
    if (plays.isEmpty() || plays == null) {
        throw new Exception ("List<Play> error");
    }
    return plays.get(0);
  }
}

当我在本地运行以下代码时，我得到正常响应:

Session session = SessionFactoryHelper.getSession();
try {
    GamePhase gp = ((Game) session.get(Game.class, 1)).getFirstPlay();
    System.out.println("GamePhaseID="+gp.getGamePhaseID());
    Play play = ((Series) session.get(Series.class, 1)).getFirstPlay();
    System.out.println("PlayID="+play.getPlayID());
}
catch (Exception e) {
  e.printStackTrace(System.out);
}

response: GamePhaseID=1 PlayID=1

当我在 JSP 中运行它时(请原谅这些 scriptlet，我仍在学习 JSTL 的基础知识)。

<% Game game = (Game) request.getAttribute("game");
List<GamePhase> series = game.getDrives(); %>
<p> <%=game.getFirstGamePhase() %> </p>

<%for (GamePhase gamePhase : series) {
      if (gamePhase.isSeries()) { 
Series series = (Series) gamePhase;%>
<table>
  <tr>
    <td> <%= series.getGamePhaseID() %>
    </td>
    <td> Play <%= series.getFirstPlay() %>
    </td>
  </tr>
</table>

getFirstPlay()方法失败，因为 List<Play>播放为空。如果我注释掉<%-- series.getFirstPlay() --%> ，代码可以正常运行并呈现良好。

据我所知，唯一的区别是 @OneToMany在Play指的是子类实体，而@OneToMany在GamePhase不...

有什么想法吗？

Answer 1

问题在于选角。

在工作示例中:

Play play = ((Series) session.get(Series.class, 1)).getFirstPlay();

在上面的场景中，您告诉 Hibernate 显式加载 ID=1 的 Series 对象 - 因此它可以正确处理急切加载，并且加载播放不会出现任何问题。

但是，在第二个示例中:

for (GamePhase gamePhase : series) {
    if (gamePhase.isSeries()) { 
        Series series = (Series) gamePhase;

这次 Hibernate 已经为您加载了 GamePhase 对象 - 当您将其转换为 Series 对象时，该方法可用，但显然 Hibernate 此时并不急于在转换中加载其他 Series 内容。