javax.persistence对field，getter或setter的注释？

问题描述

我目前正在学习Hibernate和Java Persistence API。

I am currently learning Hibernate and the Java Persistence API.

我有一个@Entity类，需要对各个字段应用注释。我已经在下面的代码中包含了他们可以去的所有三个地方。

I have an @Entity class, and need to apply annotations to the various fields. I have included in the code below all three places where they could go.

我应该将它们应用到字段本身，getter还是setter？这三个选项之间的语义差异是什么（如果有的话）。

Should I apply them to the field itself, the getter or the setter? And what is the semantic difference, if any, between these three options.

import javax.persistence.Entity;
import javax.persistence.Table;
import javax.persistence.Id;

@Entity
@Table(name = "song")
public class Song {
    // Annotations should only be applied to one of the below

    @Id
    @Column(name="id", unique=true, nullable=false)
    private int    id;

    @Id
    @Column(name="id", unique=true, nullable=false)
    public int getId() {
        return id;
    }

    @Id
    @Column(name="id", unique=true, nullable=false)
    public void setId(int id) {
        this.id = id;
    }
}

推荐答案

你必须在场和吸气之间做出选择。不支持在setter上添加注释。并且所有注释都应该在字段上，或者它们都应该在getter上：你不能混合两种方法（除非你使用注释）。

You have to choose between field and getter. Annotations on setters are not supported. And all the annotations should be on fields, or they should all be on getters: you can't mix both approaches (except if you use the @AccessType annotation).

关于哪一个更喜欢，答案是：它取决于。我更喜欢现场访问，但YMMV，并且有些情况下属性访问是可取的。请参阅。

Regarding which one is preferrale, the answer is: it depends. I prefer field access, but YMMV, and there are situations where property access is preferrable. See Hibernate Annotations - Which is better, field or property access?.

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