是否可以使用@Version替代配置?

问题描述

我在我的所有JPA域类中都在其上放置了带注释的字段，其中带有@Version，但这似乎就像是额外的模板.有没有办法通过配置解决这个问题?

TIA，奥莱(Ole)

解决方案

据JPA规范告诉我们，您不能通过配置"更改@Version批注.您可以在程序代码中使用@Version，也可以不使用.

请参考官方 JPA规范(最终版本，JPA 2.1)在第3.4.2节(第90页)中可以找到:

但是，您可以使用继承的概念通过抽象基类仅在一个位置提供@Version.该类的编写方式如下:

@MappedSuperclass
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
public abstract class AbstractBaseEntity {

    public static final long INVALID_OBJECT_ID = -42;

    @Version
    private int version;

    @Id
    @SequenceGenerator(name = "sequence-object", sequenceName = "ID_MASTER_SEQ")
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "sequence-object")
    @Column(name = "id")
    protected Long objectID = INVALID_OBJECT_ID;

    public final int getVersion() {
        return version;
    }

    @Override
    public long getObjectID() {
        return objectID;
    }

    // ... maybe other methods or fields ...
}

因此，所有从AbstractPersistentEntity继承的带@Entity注释的子类都具有两个属性:(i)objectID和(ii)version.例如，类SomeClass可以写为:

@Entity
public class SomeClass extends AbstractBaseEntity /*implements SomeInterface*/ {
    // ... specific methods or fields ...
}

有关使用@MappedSuperclass的详细信息，另请参见此答案.

希望有帮助.

I'm placing an annotated field with @Version on it in all my JPA domain classes, however this just seems like additional boiler plate. Is there a way to get around this perhaps via configuration?

TIA,Ole

解决方案

As far as the JPA specification tells us you can't change the @Version annotation via "configuration". You either use @Version in your program code or you don't.

Referring to the official JPA specification (final version, JPA 2.1) in Section 3.4.2 (page 90) we find:

However, you can use the concept of inheritance to provide the @Versiononly in one spot via an abstract base class. This class you be written as follows:

@MappedSuperclass
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
public abstract class AbstractBaseEntity {

    public static final long INVALID_OBJECT_ID = -42;

    @Version
    private int version;

    @Id
    @SequenceGenerator(name = "sequence-object", sequenceName = "ID_MASTER_SEQ")
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "sequence-object")
    @Column(name = "id")
    protected Long objectID = INVALID_OBJECT_ID;

    public final int getVersion() {
        return version;
    }

    @Override
    public long getObjectID() {
        return objectID;
    }

    // ... maybe other methods or fields ...
}

Thus, all your @Entity annotated sub-classes that inherit from AbstractPersistentEntity are provided with both properties: (i) objectIDand (ii) version at once. For instance, class SomeClass can be written as:

@Entity
public class SomeClass extends AbstractBaseEntity /*implements SomeInterface*/ {
    // ... specific methods or fields ...
}

For details on the use of @MappedSuperclass see also this answer.

Hope it helps.

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