如何使实体只读？

Question

What is the proper way to make an Entity read-only with JPA ? I wish my database table to never be modified at all programmatically.

I think I understand that I should lock my objects with LockModeType.READ . Is it possible to use an annotation to make my entities directly locked after retrieval from the database ? Or do I have to mess around and override my generic DAO for that specific entity ?

Answer 1

In your entity add an EntityListener like this:

@Entity
@EntityListeners(PreventAnyUpdate.class)
public class YourEntity {
    // ...
}

Implement your EntityListener , to throw an exception if any update occurs:

public class PreventAnyUpdate {

    @PrePersist
    void onPrePersist(Object o) {
        throw new IllegalStateException("JPA is trying to persist an entity of type " + (o == null ? "null" : o.getClass()));
    }

    @PreUpdate
    void onPreUpdate(Object o) {
        throw new IllegalStateException("JPA is trying to update an entity of type " + (o == null ? "null" : o.getClass()));
    }

    @PreRemove
    void onPreRemove(Object o) {
        throw new IllegalStateException("JPA is trying to remove an entity of type " + (o == null ? "null" : o.getClass()));
    }
}

This will create a bullet proof safety net for your entity with JPA lifecycle listeners.

• PRO: JPA standard - not hibernate specific
• PRO: very safe
• CON: only shows write attempts at runtime . If you want a compile time check, you should not implement setters.

Answer 2

A solution is to use field based annotation, to declare your fields as protected and to propose only public getter. Doing so, your objects can not be altered.

(This solution is not entity specific, it is just a way to build immutable objects)

Answer 3

Hibernate 还有一个org.hibernate.annotations.Immutable注释，你可以把它放在类型、方法或字段上。

Answer 4

If your JPA implementation is hibernate - you could use the hibernate Entity annotation

@org.hibernate.annotations.Entity(mutable = false)

Obviously this will tie your model to hibernate though.

Answer 5

IIRC you could set every field to insertable = false and updatable = false in your @Column annotations, but I'm sure there must be a better method... :)

I don't suppose this helps?

Answer 6

I think what you are looking for is your entity to be Immutable. Hibernate supports this; JPA(at least JPA 1.0) does not. I suppose you can only control this by providing only getters and make sure that the getters return only immutable values.

Answer 7

Eclipselink 实现还为您提供了实体级别的@ReadOnly注释

Answer 8

This is probably going to catch me a downvote because I always get downvoted for suggesting it, but you could use AspectJ in several ways to enforce this:

Either automate Mac's solution (make AspectJ inject the @Column annotation):

declare @field : (@Entity *) *.* : @Column(insertable=false);

Or declare a compiler error for all access to set methods:

declare error : execution((@Entity *) *.set*(*) );

Downside: you need to add AspectJ compilation to your build, but that's easy if you use ant or maven

Answer 9

If you are using spring-data or are otherwise using the Repository pattern, don't include any save / update / create / insert / etc methods in the Repository for that particular entity. This can be generalized by having a base class / interface for readonly entities, and an updatable one that extends the readonly one for updatable entities. As other posters have pointed out, the setters may also be made non-public to avoid developers accidentally setting values that they are then unable to save.