Question

I am trying to access a user object in a collection with the id = to users101 and set this to another users.

Controller.MyObject.SingleOrDefault(x => x.Id == "user101") = OtherUser();

Thanks in advance.

Answer 1

You can’t do it with one LINQ expression.

Usually LINQ extensions works on enumerables, if MyObject is a collection you first have to find the required item and then overwrite it with the new object (moreover SingleOrDefault() will simply return null if condition is not satisfied).

You should write something like this (exact code depends on what MyObject is):

var item = Controller.MyObject.SingleOrDefault(x => x.Id == "user101");
if (item != null)
    Controller.MyObject[Controller.MyObject.IndexOf(item)] = new OtherUser();

Please note that if you do not really need the check performed by SingleOrDefault() you can simplify the code (and avoid the double search performed in SingleOrDefault() and IndexOf()).

If this is “performance critical” maybe it is better to write an ad-hoc implementation that does this task in one single pass.