如何使用接口和JPA [英] How to work with interfaces and JPA

问题描述

我应该首先说我是Java EE的新手，而且我还没有很强的Java理论背景。

I should start out by saying that I am fairly new to Java EE and that I do not have a strong theoretical background in Java yet.

我有麻烦如何在Java中使用 JPA 和 interfaces 。为了说明我发现的困难，我创建了一个非常简单的例子。

I'm having trouble grasping how to use JPA together with interfaces in Java. To illustrate what I find hard I created a very simple example.

如果我有两个简单的接口 Person 和宠物：

If I have two simple interfaces Person and Pet:

public interface Person
{
    public Pet getPet();
    public void setPet(Pet pet);
}

public interface Pet
{
    public String getName();
}

和实体 PersonEntity 实现 Person 以及实现 Pet PetEntity >：

And an Entity PersonEntity which implements Person as well as a PetEntity which implements Pet:

@Entity
public class PersonEntity implements Person
{
    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    private Long id;

    private PetEntity pet;

    @Override
    public void setPet(Pet pet)
    {
        /* How do i solve this? */
    }
}

@Entity
public class PetEntity implements Pet
{
    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    private Long id;

    private String name;

    /* Getters and Setters omitted */

}

如何在 setPet 方法中正确处理案例，我想在其中保持上述两个实体之间的关系？

How do I properly handle the case in the setPet method in which I want to persist the relationships between the two entities above?

我想使用接口的主要原因是因为我想保持模块/层之间的依赖关系到公共接口。我怎样才能避免从例如我的ManagedBean直接到实体？

The main reason I want to use interfaces is because I want to keep dependencies between modules/layers to the public interfaces. How else do I avoid getting a dependency from e.g. my ManagedBean directly to an Entity?

如果有人建议不要在实体上使用接口，请说明有哪些替代方法或模式。

If someone recommends against using interfaces on entities, then please explain what alternatives methods or patterns there are.

推荐答案

您可以使用 <关系注释中的code> targetEntity 属性。

You can use targetEntity property in the relationship annotation.

@Entity
public class PersonEntity implements Person {
    private Long id;

    private Pet pet;

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    public Long getId() {
        return id;
    }

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

    @Override
    @OneToOne(targetEntity = PetEntity.class)
    public Pet getPet() {
        return pet;
    }        

    public void setPet(Pet pet) {
        this.pet = pet;
    }
}

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