LINQ query OrderBy doesn't work

Question

_db.InstellingAdressens
    .Where(l => l.GEMEENTE.Contains(gem_query))
    .OrderBy(q => q.GEMEENTE)
    .Select(q => q.GEMEENTE)
    .Distinct();

this is the query. it returns a List<string> but the strings are not ordered at all. Why does the OrderBy have no effect? and how to fix it?

Answer 1

Try putting OrderBy at the end of your call.

_db.InstellingAdressens.
    Where(l => l.GEMEENTE.Contains(gem_query)).
    Select(q=>q.GEMEENTE).Distinct().
    OrderBy(q=>q).ToList();

Answer 2

Distinct has no knowledge that you have ordered your items before it gets them, so it can't use that knowledge. As such, it has to assume the items are unordered, and will thus just do what it wants with them.

A typical implementation will use a hashtable, which isn't ordered by what you normally want the items to be ordered by, so the result from the distinct operation is an unordered set.

So as others have suggested, change the ordering of your calls to do the ordering last, and you should get what you want.