Question

I came across linq query which ends in (…).ToList().AsQueryable(). I know the use of .ToList() and .AsQueryable() separately. But, what is the outcome if both are combined? When do we need to combine them? I hope this question is not too dump question. Thanks in advance.

First query:

Dim costAmounts = (From t In model.OrderTrades                            
Join o In model.Orders On t.OrdNum Equals o.OrdNum 
Where o.ClientCode = clientNumber And o.BookDate = sysrec.ETicketsBookDate
Group t By t.Buy, t.OrdNum Into Amount = Sum(t.BuyAmount) _
Select OrdNum = OrdNum, Currency = Buy, SellAmount = Amount).ToList().AsQueryable()

Second Query:

 Dim orders = (From a In costAmounts _
                    Group Join s In settlements On s.Currency Equals a.Currency _
                        And s.OrdNum Equals a.OrdNum Into amounts = Group _
                    From g In amounts.DefaultIfEmpty _
                    Where g Is Nothing OrElse a.SellAmount - g.Paid <> 0 _
                    Select OrdNum = a.OrdNum Distinct).ToList()

Answer 1

You should never need to combine the two.

AsQueryable is there to give you lazy evaluation features, which the ToList completely negates.

So, the LINQ query is forced to be evaluated by ToList, then, the in memory list is converted to an IQueryable in order to allow… querying over it. Instead of constructing the query and only getting the results as needed.