IOrderedQueryable VS IQueryable
We have seen that , while making general LINQ query provider , we have to implement IQueryable along with IQueryProvider.
But what about the following query.
var query = (from ph in context.Photos
where ph.User == User && ph.PhotoSize == PhotoSize.Medium
&& ph.SearchText == "pocketpc, windows mobile" &&
ph.SearchMode == SearchMode.TagsOnly orderby PhotoOrder.Date_Posted descending
select ph ).Take(10).Skip(0);
As, this query has orderby clause, this will require IOrderedQueryable instead of IQueryable, or less it will end up with build error.
Now, digging deeper, what is the methodcall for orderby "item" descending/ascending
Simple order by , like orderby ph.id / orderby ph.id ascending, the internal method call is OrderBy(ph=>ph.id)
var query = from ph in context.Photos where ph.user = "jcl"
order by ph.Date_Taken select ph;
but if we use, orderby p.id descending , the internal method call will be made as OrderByDescending(ph => ph.id).Therefore, in CreateQuery<T>, we have to check for OrderByDescending and OrderBy method separately to process data accordingly.
Which could be
MethodCallExpression curentMethodcall = _expression as MethodCallExpression;
_asc = curentMethodcall.Method.Name == CallType.ORDERBYDESC ? false : true;
And during ProcessExpression , the expression breakdown will be
Memberexpresion ( for p = > p.id) or direct ConstantExpression (for p=> "Dake_take")
Source : LinqExtender
Hope this is useful