如何在LINQ中找到`Distinct`记录？

Question

I want to find distinct records in entity framework. My code is as below

var distinctYear = _objCalRepos
    .GetDetails()
    .Select(o => new CalendarList { Mdate = o.Mdate.Year.ToString() })
    .Distinct()
    .ToList();

ddlYear.DataSource = distinctYear;
ddlYear.DataTextField = "Mdate";
ddlYear.DataValueField = "Mdate";
ddlYear.DataBind();

Here Distinct not works. It will return all entries(duplicated).

Answer 1

Distinct is not working, probably because CalendarList is not comparable. Try this:

var distinctYear = _objCalRepos
    .GetDetails()
    .Select(o => o.Mdate.Year.ToString())
    .Distinct()
    .AsEnumerable()
    .Select(o => new CalendarList { Mdate = o }))
    .ToList();

Answer 2

You can use GroupBy

var distinctYear = _objCalRepos
    .GetDetails()
    .Select(o => new CalendarList { Mdate = o.Mdate.Year.ToString() })
    .GroupBy(cl => cl.Mdate )
    .Select(g => g.First())
    .ToList();