Question

I am doing an application in play framework in which I need to store the same instance of a non-Entity object into a JPA Entity without persisting it into the database, I want to know if it s possible to achieve that or not using annotations. A sample code of what I am looking for is:

 public class anEntity extends Model {
    @ManyToOne
    public User user;

    @ManyToOne
    public Question question;


    //Encrypted candidate name for the answer
    @Column(columnDefinition = "text")
    public BigInteger candidateName;

    //I want that field not to be inserted into the database
    TestObject p= new TestObject();

I tried @Embedded annotation but its supposed to embed the object fields into the entity table. Is there anyway to use @Embedded while keeping the object column hidden in the entity table?

Answer 1

查阅@Transient annotation:

“本说明具体规定,财产或田地不是持久性的。用来指实体类别的财产或领域,标明超级等级,或嵌入可使用类别。

为保证永远获得同样的目标,您可采用 http://en.wikipedia.org/wiki/Singleton_pattern” rel=“nofollow”>Singleton 型式,以便贵实体能够使用getInstance()>方法,确定瞬间物体:

因此,应当做到:

public class anEntity extends Model {
    @Transient
    private TransientSingleton t;

    public anEntity(){ // JPA calls this so you can use the constructor to set the transient instance.
        super();
        t=TransientSingleton.getInstance();
    }


public class TransientSingleton { // simple unsecure singleton from wikipedia

    private static final TransientSingleton INSTANCE = new TransientSingleton();
    private TransientSingleton() {
        [...do stuff..]
    }
    public static TransientSingleton getInstance() {
        return INSTANCE;
    }
}

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