Reasons NOT to Perform Deletes First?

Question

I ran into a problem where I was creating objects with a unique key in the same UnitOfWork where I had previously deleted an object with the same values for the unique key (the constrained columns are not in the mapped primary key). I solved the problem by calling setShouldPerformDeletesFirst(true) on my UnitOfWork. Since I hate special cases, I'm wondering whether we should perhaps just set this by default when we create a UnitOfWork. The code that creates the UnitOfWork doesn't know what will be performed in it, and the code that wants to performDeletesFirst doesn't know what else might be done in the same UnitOfWork, so it would be nice to have a consistent policy. Are there any drawbacks or potential conflicts with setting this value by default?

Answer 1

PerformDeletesFirst is definately not to be used all of the time. It is designed only for the case that you described. In fact, I recommend that you avoid creating objects with the same pk as one that ever existed in the uow. If you have to do it, then you will need to use perform deletes first, but only for this case.
If you always use performDeletesFirst, you could run into issues in cases where a delete requires an update first.
Consider:
A a = (A)uow.readObect(A.class);
B b = a.getB();
uow.deleteObject(b);
a.setB(null);
This will attempt to delete before the update is fired potentially causing a constraint error...