How to use MERGE and PERSIST cascade types on many to one save or update operation?

Question

I have a mapping like below in one of my entities. When trying to save this entity, if scrMSgLine id is already set and the cascade type is PERSIST then i got the "org.hibernate.PersistentObjectException: detached entity passed to persist: ScrMsgLine" exception. If i change the cascade type to MERGE then record is saved succesfully.

If scrMSgLine id is null and cascade type is MERGE then i got the "object references an unsaved transient instance - save the transient instance before flushing" exception.

So which cascade type should i use, what am i doing wrong ?

@ManyToOne(cascade = {CascadeType.PERSIST})
@JoinColumn(name = "MSG_LINE_ID")
@Where(clause = "DELETED_AT IS NULL")
public ScrMsgLine getScrMsgLine() {
    return scrMsgLine;
}

Answer 1

It turned out to be a transaction problem instead of cascade type. I was creating a new tnx after saving the scrMsgLine object. So it was becoming detached when i pass it to the new tnx. As a work around i read it from db in the begining of the new tnx. And i changed the cascade type to PERSIST. I am not sure if this is the right solution but for now it works for me...

Answer 2

To avoid exceptions; use merge method to save your objects instead of persist and use CascadeType.ALL on ScrMsgLine.

As long as your relationships are set to CascadeType.ALL, you could always change your em.persist(exam); to em.merge(exam);. That would take care of persisting the new object, and it would also cascade the merge call to the ScrMsgLine.

And this Q&A may be more helpful.

I hope it helps.