Exception when adding a toList() at the query? (C#) [duplicate]

Question

This question already has an answer here:

Why a simple linq command is not executed at the second case? (1 answer)

Closed 8 years ago.

I have the following query

var query = (from b in db.StudentProgressPerDay
             where b.Student.Equals(InputStudent)
             orderby b.Date
             select b);

and the following command which is runs ok

var dates = query.Select(x => EntityFunctions.DiffDays(query.Min(y => y.Date), x.Date));

When I add a toList() command at the end, the aforementioned function does not work but instead it gives an exception

An exception of type 'System.NotSupportedException' occurred in System.Data.Entity.dll but was not handled in user code

Answer 1

EntityFunctions is specific to Linq-to-Entities. ToList creates a regular List, so any queries on the list will be Linq-to-Objects from that point.

Try the following:

var query = (from b in db.StudentProgressPerDay
                         where b.Student.Equals(InputStudent)
                         orderby b.Date
                         select b).ToList();

var dates = list.Select(x => (x.Date - query.Min(y => y.Date)).Days);