Question

How do I combine these two methods into one?

public override Expression<Func<Attachment, bool>> MatchingCriteria
{
  get { return a => a.Activity.Parent.ActivityUsers.Any(x => (x.User.Id == id)); }
}

and

public override Expression<Func<Attachment, bool>> MatchingCriteria
{
  get { return a => a.Activity.ActivityUsers.Any(x => (x.User.Id == id)); }
}

notably, the idea is that I want to check the root record for links to a certain User. But, a may be a root or may be a child (one decendant/level only; not recursive). I want an ORing, so to speak, of these two Linq expressions.

Answer 1

Maybe something like:

public override Expression<Func<Attachment, bool>> MatchingCriteria
{
  get 
  {
     return a => a.Activity.Parent.ActivityUsers
                  .Concat(a.Activity.ActivityUsers).Any(x => (x.User.Id == id));
  }
}

Or since you’re only worried about a single level deep you could probably use:

public override Expression<Func<Attachment, bool>> MatchingCriteria
{
  get 
  {
     return a => a.Activity.Parent.Any(a2 => 
         a2.ActivityUsers.Any(x => 
             (x.User.Id == id) || x.Activity.ActivityUsers.Any(y =>
                 y.User.Id == id)));
  }
}

This option is probably more appropriate.