Last and LastOrDefault not supported

• Instead of putting it into an own list by calling ToList() or ToArray() i would prefer to use AsEnumerable().
• Additionally like the others you should try OrderByDescending()
• Instead of Count() i would use Any().

either you switch your OrderBy to

.OrderByDescending(p => p.BillID)

(and use first) or you do something like

purchaseBills.ToArray().Last()

if this is not to expensive.

Last is not supported by the back-end DB. You should try other techniques:

1. Run your query using OrderByDescending so your requested item comes first.

2. Code your LINQ query as usual, but enforce Linq2Sql to render it to a CLR collection and then you'll have free access to everything locally, including Last. Example:

   var bills = purchaseBills.ToList();
   var last = bills.Last();
   

The problem is that there's no easy translation into SQL for Last or Reverse, so either convert it to something in memory (ToList, ToArray) if there aren't going to be too many records, or you could run the query a 2nd time, with OrderByDescending instead of OrderBy and use First.