Java 带有休眠注释的接口
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Interfaces with hibernate annotations
提问by molleman
i am wondering how i would be able to annotate an interface
我想知道如何才能注释接口
@Entity
@Table(name = "FOLDER_TABLE")
public class Folder implements Serializable, Hierarchy {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
@Column(name = "folder_id", updatable = false, nullable = false)
private int fId;
@Column(name = "folder_name")
private String folderName;
@OneToMany(cascade = CascadeType.ALL)
@JoinTable(name = "FOLDER_JOIN_FILE_INFORMATION_TABLE", joinColumns =
{ @JoinColumn(name = "folder_id") }, inverseJoinColumns =
{ @JoinColumn(name = "file_information_id") })
private List< Hierarchy > fileInformation = new ArrayList< Hierarchy >();
}
above and below are 2 classes that implement an interface called Hierarchy, the folder class has a list of Hierarchyies being a folder or a fileinformation class
上面和下面是 2 个实现名为 Hierarchy 的接口的类，文件夹类有一个层次结构列表，即文件夹或文件信息类
@Entity
@Table(name = "FILE_INFORMATION_TABLE")
public class FileInformation implements Serializable, Hierarchy {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
@Column(name = "file_information_id", updatable = false, nullable = false)
private int ieId;
@Column (name = "location")
private String location;
}
I have searched the web for someway to annotate or a workaround but I cannot map the interface which is simply this
我在网上搜索了一些注释或解决方法，但我无法映射界面，这就是这个
public interface Hierarchy {
}
I get a mapping exception on the List of hierarchies with a folder but I don't know how to map the class correctly.
我在带有文件夹的层次结构列表中遇到映射异常，但我不知道如何正确映射类。
回答by Kris
A little Googling turned up...
一个小小的谷歌搜索出现了......
You can use interfaces internally but you can't map interfaces in hibernate, you have to map classes, regardless of whether you are using xml mapping or annotation mapping. hibernate is handling lifecycle of your persistent objects so it needs to know what class to instantiate so you need to provide this information to it... I am not even sure how what you suggesting would even look like? how would you provide implementation for given interface to hibernate at runtime to instantiate?
您可以在内部使用接口，但 不能在 hibernate 中映射接口，您必须映射类，无论您使用的是 xml 映射还是注释映射。hibernate 正在处理持久对象的生命周期，因此它需要知道要实例化哪个类，因此您需要向它提供此信息……我什至不确定您的建议会是什么样子？您将如何为给定的接口提供实现以在运行时休眠以实例化？
http://forum.springsource.org/showthread.php?t=67420
http://forum.springsource.org/showthread.php?t=67420
So it looks like you are out of luck.
所以看起来你运气不好。
回答by Péter T?r?k
You can map interfaces in Hibernate, as part of inheritance hierarchies. This is quite surely possible with XML mapping, as it is described in Chapter 9 of the Hibernate reference, among others.
您可以在 Hibernate 中映射接口，作为继承层次结构的一部分。这对于 XML 映射来说肯定是可能的，正如Hibernate 参考资料 的第 9 章中所描述的那样。
Annotation based mapping is a different story though. I am not so familiar with it, but Java Persistence with Hibernateincludes examples for this too. Adapted to your case, it would look like
但基于注释的映射是另一回事。我对它不太熟悉，但是Java Persistence with Hibernate 也包含了这方面的示例。适应你的情况，它看起来像
@MappedSuperclass
public interface Hierarchy {
}
@Entity
@Table(name = "FOLDER_TABLE")
public class Folder implements Serializable, Hierarchy { ... }
@Entity
@Table(name = "FILE_INFORMATION_TABLE")
public class FileInformation implements Serializable, Hierarchy { ... }
This mapping would use a table per concrete class with implicit polymorphism.
此映射将使用具有隐式多态性的每个具体类使用一个表。
However, other sources suggest that annotation support for interfaces may not be working / stable yet:
但是，其他来源表明接口的注释支持可能还没有工作/稳定：
- there is a related open bug reporton using the
@Entityannotation with interfaces, which also includes some patches, - here is a related (fairly old) thread, describing a workaround using XML mapping.
- 有一个关于在
@Entity接口中使用注释的相关公开错误报告，其中还包括一些补丁， - 这是一个相关的（相当老的）线程，描述了使用 XML 映射的解决方法。
So you may need to experiment, including changing your inheritance mapping strategy, maybe turning the interface into an abstract class (if it's possible - since a class can only extend a single base class)...
所以你可能需要进行试验，包括改变你的继承映射策略，也许把接口变成一个抽象类（如果可能的话——因为一个类只能扩展一个基类）......
