Question

First Table is the View and Second is the result I want

This below query works fine

List<BTWStudents> students = (from V in db.vwStudentCoursesSD
        where classIds.Contains(V.Class.Value)
        select new BTWStudents
                    {
                    StudentId = V.StudentId
                    Amount= V.PaymentMethod == "Cashier Check" ? V.Amount: "0.00"
                    }).Distinct().ToList();

But I changed it to List to add string formatting(see below)

List<BTWStudents> students = (from V in db.vwStudentCoursesSD
        where classIds.Contains(V.Class.Value)
        select new {V}).ToList().Select(x => new BTWStudents
                    {
                    StudentId = V.StudentId
                    Amount= V.PaymentMethod == "Cashier Check" ? String.Format("{0:c}",V.Amount): "0.00"
                    }).Distinct().ToList();

With this Second Query I get this

Why is distinct not working in the second query?

Answer 1

When working with objects (in your case a wrapped anonymous type because you are using Select new {V} rather than just Select V), Distinct calls the object.Equals when doing the comparison. Internally, this checks the object’s hash code. You’ll find in this case, the hash code of the two objects is different even though the fields contain the same values. To fix this, you will need to override Equals on the object type or pass a custom IEqualityComparer implementation into the Distinct overload. You should be able to find a number of examples online searching for “Distinct IEqualityComparer”.