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我正在尝试制作一个可以在 ObjectDB 数据库（嵌入）中存储包含文件和文件夹的树结构的应用程序，但即使进行简单测试，我仍然会收到错误消息...

实体类

节点.java

@MappedSuperclass
public abstract class Node {

    @Column(name = "Name", nullable = false)
    private String name;

    @Column(name = "Parent_FK")
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "FolderID", nullable = true)
    private FolderNode parent = null;

    public Node() {
    }

    public Node(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public boolean hasParent() {
        return (parent != null);
    }

    public FolderNode getParent() {
        return parent;
    }

    void setParent(FolderNode parent) {
        this.parent = parent;
    }

    @Override
    public int hashCode() {
        return new HashCodeBuilder(17, 31).append(name).toHashCode();
    }

    @Override
    public boolean equals(Object obj) {
        if (obj == null) {
            return false;
        }
        if (obj == this) {
            return true;
        }
        if (obj instanceof Label) { // TODO is instanceof enough??
            Label other = (Label) obj;
            return name.equals(other.getName());
        }
        return false;
    }
}

文件夹节点.java

@Entity(name = "Folders")
public class FolderNode extends Node {

    @Column(name = "FolderID")
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long id;

    @OneToMany(cascade = CascadeType.ALL, mappedBy = "parent", fetch = FetchType.LAZY, orphanRemoval = true)
    private Set<Node> children = new HashSet<Node>();

    public FolderNode() {
    }

    public FolderNode(String name) {
        super(name);
    }

    public Set<Node> getChildren() {
        return children;
    }

    public void setChildren(Set<Node> children) {
        this.children = children;
    }

    public long getId() {
        return id;
    }

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

调用代码

//Init
EntityManagerFactory emf = Persistence.createEntityManagerFactory("database.odb");
EntityManager em = emf.createEntityManager();

//Create object
FolderNode rootFolder = new FolderNode("root");

//Persist
em.getTransaction().begin();
em.persist(rootFolder);
em.getTransaction().commit();

em.close();
emf.close();

emf = Persistence.createEntityManagerFactory("database.odb");
em = emf.createEntityManager();

TypedQuery<FolderNode> query = em.createQuery("SELECT f FROM Folders f", FolderNode.class);
List<FolderNode> result = query.getResultList();

这就是它崩溃的地方，但有一个例外：

[ObjectDB 2.3.5_07] javax.persistence.PersistenceException
Failed to write the value of field field FolderNode.children using reflection (error 363)

如果我在获取对象之前不关闭并重新打开 EntityManagerFactory 和 EntityManager，问题似乎就消失了。

我在这里想念什么？

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1 回答 1

2

您的代码演示了处理映射超类的问题。如果您将 @MappedSuperclass 注释替换为 @Entity（对于 Node 类），您的测试将运行良好。

ObjectDB 应该将映射的超类作为实体类处理，因此按照您的帖子 - 此问题已得到修复，您的测试（使用 @MappedSuperclass）应该适用于 build 2.3.6_14。

于 2012-01-20T15:05:10.820 回答