LINQ: Remove items from IQueryable

Question

I want to remove an item from the result of a LINQ query before using it to databind. What is the proper way to do this?

The foreach in my illustration is the topic of my question. Illustration:

var obj =
    (from a in dc.Activities
    where a.Referrer != null
    && a.Referrer.Trim().Length > 12
    && a.Session.IP.NumProblems == 0
    && (a.Session.UID == null || a.Session.UID < 1 || a.Session.User.BanLevel < 1)
    select a)
    .Take(int.Parse(ConfigurationManager.AppSettings["RecentItemQty"]));
foreach (Activity act in obj)
    if (isDomainBlacklisted(ref dc, act.Referrer))
        obj.Remove(act);

Solution 1

You don't need the foreach you could just use this...

obj.RemoveAll(act => isDomainBlackListed(ref dc, act.Referrer));

Solution 2

You can just put it at the end of the query to filter them out before they even end up in the result:

var obj =
   (from a in dc.Activities
   where a.Referrer != null
   && a.Referrer.Trim().Length > 12
   && a.Session.IP.NumProblems == 0
   && (a.Session.UID == null || a.Session.UID < 1 || a.Session.User.BanLevel < 1)
   select a)
   .Take(int.Parse(ConfigurationManager.AppSettings["RecentItemQty"]))
   .Where(a => !isDomainBlacklisted(ref dc, a.Referrer));

You can put the Where before the Take if you want other items to replace the ones filtered out, but that means more calls to isDomainBlacklisted of course.