Question

During my web application development in asp.net I am facing following error,
No coercion operator is defined between types <>f__AnonymousType01[System.Collections.Generic.IEnumerable1[clsDAL.AnsType]]’ and ‘clsDAL.AnsType’.

This error accruing when I am fetching data from Database using LInqToSQL. The function in which this error accruing is as below.

public static IList<AnsType> GetAnswer(int id)
{            
    var TempAns = GlobalClass.DBContext.tbQueAns.Where(s => s.QueId == id).Select(s => s.AnsVal).ToList();
    var TAns = GlobalClass.DBContext.tbQueOptions.Where(s=>s.QueId == id).Join(GlobalClass.DBContext.tbQueAns, x => x.OptionId, s => s.AnsVal, (a, b) => new { ans = a.OptionVal });
    List<AnsType> Ans = TAns.Cast<AnsType>().ToList();
    return Ans;
} 

And the type of AnsType is as below…

public class AnsType
{
    public string AnsVal { get; set; }
}

I am didn’t getting understand what is exactly going on, I had also try to search this problem on Google but I didn’t getting answer.
And I also want to know the reasons of accruing this error.

Answer 1

This should work:

  var TAns = GlobalClass.DBContext
             .tbQueOptions.Where(s=>s.QueId == id)
             .Join(GlobalClass.DBContext.tbQueAns, 
                   x => x.OptionId, 
                   s => s.AnsVal, 
                  (a, b) => new AnsType() { AnsVal = a.OptionVal }).ToList();

return TAns;  

The reason it happens, is because you’re trying to implicitly cast anonymous type and you cannot do that.

Alliteratively, you can specify a conversion operator like this:

       public class AnsType
        {
            public string AnsVal { get; set; }
            public static implicit operator AnsType(string val)
            {
                AnsType t = new AnsType();
                t.AnsVal = val;
                return t;
            }
        }  

and then use it like this: List<AnsType> Ans = TAns.Select(x=>x.ans).Cast<AnsType>().ToList();