Question

我的hibernate数据库连接出了问题。起初我发布了一些数据：

Objects.java：

@Entity
@Table (name = "objects", schema="genmeta")
public class Objects {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int o_id;
    private String o_name;
    private String o_desc;
    @ManyToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY)
    @JoinTable(name = "genmeta.object_tg_assc", joinColumns = { @JoinColumn(name = "o_id") }, inverseJoinColumns = { @JoinColumn(name = "tg_id") })
    private Set<TemplateGroup> templateGroups;
    @Transient
    private boolean templateGroupsLoaded = false;

    /**
     * Getters and Setters 
     */
}

TemplateGroup.java：

public class TemplateGroup {
    @Id
    @Column(unique=true, nullable=false)
    private int tg_id;
    private String tg_name;
    private String tg_desc;
    @ManyToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY, mappedBy = "templateGroups")
    private Set<Objects> objects;

    /**
     * Getters and Setters 
     */
}

我的问题是，我以后如何从我的类Object获取数据？

这是我的第一次尝试：代码示例：

public Set<TemplateGroup> loadTemplateGroups(Objects myObjects) {
    Session session = factory.openSession();
    Set<TemplateGroup> myTG = myObjects.getTemplateGroups();
    session.close();
    return myTG;
}

非常感谢。

祝你好运的Björn

Answer 1

抛出failed to lazily initialize a collection of role: db.hibernate.classes.Objects.templateGroups, could not initialize proxy - no Session异常是因为您正在一个事务中检索Objects实例并在另一个事务中调用getTemplateGroups()（或在第一个事务提交之后）。您不应该打开另一个会话来获取模板组。

您需要执行以下操作：

Session session = factory.openSession();
Objects object = <Code to retrieve the Objects instance>
Set<TemplateGroup> templateGroups = object.getTemplateGroups();
templateGroups.size(); // as an example
session.close();

以多对多连接获取数据

1 个答案: