C# preventing Collection Was Modified exception

Question

Does

 foreach(T value in new List(oldList) )

is dangerous (costly) when oldList contains 1 millions of object T ?

More g

Answer 1

For me, first thing is you should consider using some kind of data paging, because having such 1-milion-items-large list could be dangerous itself.

Have you heard about Unit of Work pattern?

You can implement it so you mark objects for create, update or delete, and later, you call "SaveChanges", "Commit" or any other doing the job of "apply changes", and you'll get done.

For example, you iterate over the enumerable (oldList) and you mark them as "delete". Later, you call "SaveChanges" and the more abstract, generic unit of work will iterate over the small, filtered list of objects to work with.

• http://martinfowler.com/eaaCatalog/unitOfWork.html

Anyway, avoid lists of a milion items. You should work with paged lists of objects.