How To Bind Linq Join With ViewModel In Asp.net MVC?

Question

Here I am trying to get the list by joining two table using LINQ and I want ContestantId from ContestantRatings table. But it shows an error in line ContestantId = Convert.ToInt32(CR.ContestantId) which says: 'LINQ to Entities does not recognize the method Int32 ToInt32(System.Object) method, and this method cannot be translated into a store expression.' .
Any help will be highly appreciated.

Below is my code

public List<ContestantRating.Core.ViewModel.ContestantRatingVM> GetContestantRatingList()
{
    var contestantRatingList = (from C in db.Contestants where C.IsActive==true
                                join CR in db.ContestantRatings on C.Id equals CR.ContestantId 
                                select new ContestantRatingVM
                                {
                                    ContestantId  = Convert.ToInt32(CR.ContestantId),
                                    FirstName = C.FirstName,
                                    LastName = C.LastName,
                                    DateOfBirth = C.DateOfBirth,
                                    District = C.District.DistrictName,
                                    Rating = CR.Rating,
                                    RatingId = CR.Id,
                                    RatedDate=CR.RatedDate
                                }).ToList().OrderByDescending(x => x.RatingId);
    return contestantRatingList.ToList();
}

Below is my viewmodel ContestantRatingVM which I used

public class ContestantRatingVM
{
    public int  ContestantId { get; set; }
    public Nullable<int> HomeZoneId { get; set; }
    public string District { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public Nullable<System.DateTime> DateOfBirth { get; set; }
    public Nullable<bool> IsActive { get; set; }
    public string Gender { get; set; }
    public string PhotoUrl { get; set; }
    public string Address { get; set; }
    public int RatingId { get; set; }
    public Nullable<decimal> Rating { get; set; }
    public Nullable<System.DateTime> RatedDate { get; set; }
}

Answer 1

The problem is the call to Convert.ToInt32 . Linq to entities converts the Linq query to a database query and thus has a limited set of operations it supports. In order to solve this, you have several options.

One option is to do the conversion after the database query:

public List<ContestantRating.Core.ViewModel.ContestantRatingVM> GetContestantRatingList()
{
  var tempArray = (from c in db.Contestants where C.IsActive==true
                   join cr in db.ContestantRatings on C.Id equals CR.ContestantId 
                   select new { C = c, CR = cr }).ToArray();
  var contestantRatingList = from x in tempArray select new ContestantRatingVM
                                {
                                    ContestantId  = Convert.ToInt32(x.CR.ContestantId),
                                    FirstName = x.C.FirstName,
                                    // ...
                                }).ToList().OrderByDescending(x => x.RatingId);
  return contestantRatingList.ToList();
}

By calling ToArray , you send the query to the database, so that Linq to Enities does not have to deal with Convert.ToInt32 .