How to modify an item in an IEnumarable collection and retain its order

Question

Hi,

I have the following situation. I have a list of items which have an "Id". I have to search for an item with a specific id, modify its values and maintain the order of the collection. What would be the best way to do that?

var collection = <some_linq_query>

collection.Where(i=>i.Id=someId).FirstOrDefault().Property = "bla";

// now collection should be the same but the item updated.

Answer 1

As long as the objects in the collection are mutable, your code should work fine.

By the way, FirstOrDefault takes an optional filter parameter, so you can write collection.FirstOrDefault(i => i.Id == someId).

Answer 2

The call to Where does not modify the original LINQ query stored in collection in any way. Instead it creates a new IEnumerable<T> where is a subset of the original query. The subset will have the same relative ordering as the original set in collection

The only way this could cause a problem is if the value collection is a LINQ where which has a Where clause, or is otherwise filtered, base on the value of Property. If that is the case and you want to preserve the order force collection into a non-lazy evaluated structure via .ToList.

collection = collection.ToList();