LInq-to-sql dynamic sorting problem - linq-to-sql

Question

I have a linq-to-sql query over entity that has child entityset that I need to sort on some child fields, i.e. use this query:
var query = from p in context.Patients
let order = p.Lab_Orders.First()
orderby order.Order_Date
select p;
This query runs fine, but how would I modify it to use DLINQ OrderBy method what would I pass as a sorting parameter in run-time?

Answer 1

If by DLINQ you mean Dynamic Query, then you can't use the query expressions like that, you have to use extension methods with lambdas. You can start with a query expression but you have to eventually switch it over to lambda:
IEnumerable<Patient> GetPatients(string orderSortField)
{
var query =
from p in context.Patients
select new
{
Patient = p,
FirstOrder = p.Lab_Orders.First()
};
return p.OrderBy(orderSortField).Select(p => p.Patient);
}
Call it with:
var patientsByOrderDate = GetPatients("FirstOrder.Order_Date");

Answer 2

Use the AsQueryable() after the initial statement -
var query = from p in context.Patients
let order = p.Lab_Orders.First()
select p;
query = query.AsQueryable().OrderBy(x => x.Lab_Orders.First().OrderDate);

Answer 3

Try to add the "OrderBy" to the expression tree:
var query = from p in context.Patients
let order = p.Lab_Orders.First()
select p;
var x = Expression.Parameter(query.ElementType, "x");
string sortName = "order.Order_Date";
var selector = Expression.Lambda(Expression.PropertyOrField(x, sortName), x);
query = query.Provider.CreateQuery(
Expression.Call(typeof(Queryable), "OrderBy",
new Type[] { query.ElementType, selector.Body.Type },
query.Expression, selector)
) as IQueryable<Patients>;
Needs the namespace "System.Linq.Expressions".