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CascadeType.Merge in entity relations with Spring Data

Igor Gorbunov
Igor Gorbunov Published in 2017-12-07 08:52:54Z

I have two entities (Consultancy - the owner, and InterviewType) with @ManyToMany bidirectional relations. User can attach the interview type to the Consultancy. I know that in a case of we're using a Hibernate we can just invoke merge() method on EntityManager to persist a new transient entity or update a detach object, but what about save() method in Spring Data or Spring Data have another method? Does it make some effect on a depend entity of a @ManyToMany relations? In case of 'yes' in what way? Does it invoke a Hibernates merge() method under the hood?

Maciej Kowalski
Maciej Kowalski Reply to 2017-12-07 09:01:41Z

If you look at the implementation from the 2.0.2 version:

public <S extends T> S save(S entity) {

    if (entityInformation.isNew(entity)) {
        return entity;
    } else {
        return em.merge(entity);

The merge is invoked under the hood if the persistence provider decides that the passed entity new.. does not have an id / is not managed by the persistence provider.. So that 'new' depends a bit on the underlying implementation of the EntityInformation.

In general it should invoke the merge when there is a need though i had situations where I had to write my own custom merge logic as the implicit merge was not ivoked

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