Question

Here the code which i have written, I am getting error as soon as i added the line to call the second function which is ValidCodes = GetValidCodes(bv.Variable_Id)

public IQueryable<BvIndexRow> GetBenefitVariableIndex(int healthPlanId)
{
    var q = from bv in Db.BenefitVariables
            where bv.Private == "N" || (bv.Private == "Y" && bv.Health_Plan_ID == healthPlanId)
            join bao in Db.baObject on bv.Variable_Id equals bao.ba_Object_id
            join servicetype in Db.BenefitVariableServiceTypes.Where(bvst => bvst.Key_Service_Type == "Y" && bvst.isActive == 1) 
            on bv.Variable_Id equals servicetype.Variable_Id into groupedBvst
            where bv.isActive == 1 && bao.isActive == 1 
            from bvst in groupedBvst.DefaultIfEmpty()
            select new BvIndexRow
            {
                // some code here too
                ValidCodes = GetValidCodes(bv.Variable_Id)
            };
    return q;
}

public string GetValidCodes(int varID)
{
    // some code here
    return "None";
}

Answer 1

Another poster has answered why, but not what to do. The why is that the method call cannot be translated by Linq-to-SQL into SQL, as it’s… not part of SQL! This makes perfect sense! So an easy way to fix this is:

public IQueryable<BvIndexRow> GetBenefitVariableIndex(int healthPlanId)
{
   var q = (... your query ...
      select new BvIndexRow
      {
         Type = (bv.Private.ToLower() == "y" ? "Private " : "Public ") + (bao.ba_system_variable_ind ? "System" : "Benefit"),
         Class = bv.Variable_Classification,
         ServiceType = bvst.Service_Type.Service_Type_Name ?? string.Empty,
         LineOfBusiness = bv.LOB,
         Status = bv.Status.ToLower() == "p" ? "Production" : "Test",
         Name = bao.ba_object_Code,
         Description = bao.ba_Object_Desc,
         Id = bv.Variable_Id,
      }).ToArray();

   foreach (var bvIndexRow in q) {
      bvIndexRow.ValidCodes = GetValidCodes(bvIndexRow .Variable_Id);
   }

   return q;
}

This should give you want you want!

EDIT: By the by, you probably also want to call .ToList() or .ToArray() on your list of BvIndexRows. This has the effect of causing immediate evaluation and will prevent a multiple enumeration. If you don’t want immediate evaluation you may need to edit your question to explain why that’s the case. I’ve added a .ToArray() to the example above, but I also wanted to explain why!