c# Build Error with LINQ syntax in Controller

Hi folks I have the following error on line 11 in this controller code :

    public JsonResult GetChartData_IncidentsBySiteStatus(string SiteTypeId, string searchTextSite, string StartDate, string EndDate)
    {
        if (searchTextSite == null)
            searchTextSite = "";

        DateTime startDate = DateTime.Parse(StartDate);
        DateTime endDate = DateTime.Parse(EndDate);

        var sitesQry = _db.Sites;
        if (SiteTypeId != "-1")
            sitesQry = sitesQry.Where(a => a.SiteTypeId.ToString() == SiteTypeId);

        var qry = from i in _db.Incidents   
                  join s in _db.Sites on i.SiteId equals s.SiteId
                  where s.SiteDescription.Contains(searchTextSite)
                    && (i.Entered >= startDate && i.Entered <= endDate)
                  group s by s.SiteStatus.SiteStatusDescription + "[" + s.SiteTypeId.ToString() + "]"
                      into grp
                      select new
                      {
                          Site = grp.Key,
                          Count = grp.Count()
                      };

        return Json(qry.ToList()  , JsonRequestBehavior.AllowGet);
    }

...........the error is:

Error 7 Cannot implicitly convert type 'System.Linq.IQueryable' to 'System.Data.Linq.Table'. An explicit conversion exists (are you missing a cast?) C:\Documents and Settings\Administrator\Desktop\IRenewables_EMAS\IRenewables_EMAS\Controllers\IncidentController.cs 69 28 Emas.Web

Can anyone suggest a work开发者_JAVA技巧around for this?

thanks

You are trying to assign a base class instance to a sub class instance.

Instead of

var sitesQry = _db.Sites;

try using

IQueryable<Site> sitesQry = _db.Sites;

While @Eranga 's solution may work, I feel as though there are more options and a better explanation available.

Firstly, the reason that you cannot assign the value is because you are trying to assign and implementation of an interface to a concrete type. THis cannot be done because you have no idea what could be implementing that interface, and this means that the it cannot be assigned to something that has a concrete type.

There are multiple options for this. You can do as @Eranga suggests and create a new variable

IQueryable<Site> sitesQry = _db.Sites;

or you can call the .CopyToDataTable extension method that is exposed by Linq.

sitesQry = _db.Sites.CopyToDataTable();