Assigning values inside a LINQ Select?

Question

I have the following query:

drivers.Select(d => { d.id = 0; d.updated = DateTime.Now; return d; }).ToList();

drivers is a List which comes in with different id's and updated values, so I am changing the values in the Select, but is the proper way to do it. I already know that I am not reassigning drivers to drivers because Resharper complains about it, so I guess it would be better if it was:

drivers = drivers.Select(d => { d.id = 0; d.updated = DateTime.Now; return d; }).ToList();

but is this still the way someone should assign new values to each element in the drivers List?

Answer 1

Although this looks innocent, especially in combination with a ToList call that executes the code immediately, I would definitely stay away from modifying anything as part of a query: the trick is so unusual that it would trip up readers of your program, even experienced ones, especially if they never saw this before.

There's nothing wrong with foreach loops - the fact that you can do it with LINQ does not mean that you should be doing it.

Answer 2

NEVER DO THIS. A query should be a query; it should be non-destructively asking questions of a data source. If you want to cause a side effect then use a foreach loop; that's what it's for. Use the right tool for the job.