CODEWITHSUNDEEP
javahibernatejpatransient
xing
xing

Reputation: 484

How to calculate a persistent property based on transient property before persist?

Say I have a persistent property A in an entity, and 2 transient fields T1, T2. When the entity is persisted, I need to calculate A based on T1, T2 (suppose this is a legacy database which can not be altered).

@Entity
Class MyEntity {
    @Column(name="persistantA")
    Integer A;

    @Transient
    Integer T1;

    @Transient
    Integer T2;

    @PrePersist
    void prePersist() {
        A = T1 * T2;
    }
}

However inside the prePersist() method all transient fields are cleared --- they are set to their initial value --- and this seems to be the proper behavior for Hibernate/Jpa.

How to overcome this?

I am using Spring boot with Jpa and Hibernate.

Upvotes: 2

Views: 616

Answers (1)

Dragan Bozanovic
Dragan Bozanovic

Reputation: 23552

If you persist a new entity by calling EntityManager::persist, then the behaviour you describe will not happen and transient fields will be visible in the @PrePersist method.

However, if you persist a new entity with EntityManager::merge, then the merging mechanism will ignore transient fields, which is expected behaviour - only the properties that Hibernate is aware of are merged. Keep in mind that merge always returns a copy (except when the argument is already a managed instance), so you have to copy transient fields manually into the result of the merge operation.

Upvotes: 1

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