Why JPA Transient annotation have method in Target?

Question

Can anyone explain using an example as to why the @Transient annotation in JPA has @Target method as well?

I am referring to documentation http://docs.oracle.com/javaee/5/api/javax/persistence/Transient.html

@Target(value={METHOD,FIELD})

Thanks in advance!

you can access transient attribute by getter method or field, that's why it has — Saravana
How does it make sense to allow it on methods? allowing only on fields shouldn't be enough? — user2906555
no, you can program to access field using reflection or getter methods. — Saravana
That is nothing to do with JPA and just basic java annotations. — Neil Stockton

Predrag Maric Predrag Maric · Accepted Answer · 2016-07-26T11:53:37

In JPA entity you can annotate fields or methods (getters). The @Id annotation dictates this, meaning if you put @Id on a field then all your annotations should go on fields but if you put it on, for example, @Id Long getId() then other annotations should follow. That's why @Transient can be on a method as well.

For example, if you have this

@Id
private Long id;

@Transient
private String someTransientField;

private Long getId() {
    return this.id;
}

private String getSomeTransientField() {
    return this.someTransientField;
}

then someTransientField would be treated as transient. But if @Id would stay on the field, and you move @Transient to private String getSomeTransientField() then someTransientField would be treated as persistent, since @Id is on the field and therefore all other annotations are expected to be on fields as well.

So the case where @Transient would work on the method is this

private Long id;

private String someTransientField;

@Id
private Long getId() {
    return this.id;
}

@Transient
private String getSomeTransientField() {
    return this.someTransientField;
}

Why JPA Transient annotation have method in Target?

3 Answers