Returning a Distinct IQueryable with LINQ?

If you limit the objects you are returning to only the fields that you want to display, it will work properly.

public static IQueryable GetActiveEmployees_Grid(string Period)
{
    DataContext Data = new DataContext();
    var Employees = (from c in DataSystem_Records
                     where c.Period == Period
                     orderby c.DataSystem_Employees.LName
                     select c.DataSystem_Employees.FName, 
                            c.DataSystem_Employees.LName, 
                            c.ID).Distinct();

    return Employees;
}

Making some assumptions around the names of the various fields in the objects:

public static IQueryable GetActiveEmployees_Grid(string Period)
{
    DataContext Data = new DataContext();
    var Employees = (from c in DataSystem_Records
                     where c.Period == Period
                     orderby c.DataSystem_Employees.LName
                     select new { FirstName = c.DataSystem_Employees.FName, LastName = c.DataSystem_Employees.LName, ID = c.DataSystem_Employees.ID }).Distinct();

    return Employees;
}

To follow the MVC pattern you might want to lift this query into your Model and return a specific class that contains those fields.

try and write an IEqualityComparer<T> for the object type being selected and use it in your Distinct method

Simplest way I have found to do this with object is using the groupby then selecting the first.

public static IQueryable GetActiveEmployees_Grid(string Period)
{
    DataContext Data = new DataContext();
    var Employees = (from c in DataSystem_Records
                     where c.Period == Period
                     orderby c.DataSystem_Employees.LName
                     select c).GroupBy(g=>g.DataSystem_Employees.AccID).Select(x=>x.FirstOrDefault());

    return Employees;
}

This is not tested but the general concept is there.

Edit: I remembered originally finding the answer somewhere on here. Check out this for grouping objects by a certain property. LINQ's Distinct() on a particular property