What is the Difference Between Merge and Persist?

[mduffy_lists]

In a basic sense it seems that

persist = INSERT
merge = UPDATE

In practice, a new entity that contains a detached entity cannot be persisted (exception: detached entity passed to persist:); however, a new entity that contains a detached entity can be merged.

I haven't tried it, but it seems that a new entity that does not contain a detached entity could also be merged. So in practice, why not forget about persist and just use merge?

Thx.

Mike

[epbernard]

Merge != update

persist could avoid some extra Select to detect whether the object is in DB or not

[mduffy_lists]

If it is just a matter of saving some overhead, then it seems that it would be good practice to use merge instead of persist whenever a new entity could possibly contain a detached entity (because in this case if you use persist, an exception is thrown).

Any thoughts on this?

Mike

[epbernard]

some people does not consider it as a small overhead, but yes in not critical path, you can use it.