Trying to modify your code hope it helps. :)
public List<salarymonthlyviewmodel> getallemployeeSalary()
{
var data = (from a in objentity.TblSalaryMonthlies
join b in objentity.TblEmployeeRegistrations on a.EmployeeId equals b.EmployeeId
select new SalaryMonthlyViewModel
{
SalaryMonthlyId = a.SalaryMonthlyId,
Month = a.Month,
Year = a.Year,
NetSalary = a.NetSalary,
PresentDay = a.PresentDay,
UserName = b.UserName
}).ToList()
.Select(c => new SalaryMonthlyViewModel()
{
SalaryMonthlyId = a.SalaryMonthlyId,
Month = a.Month,
Year = a.Year,
NetSalary = Convert.ToInt32(a.NetSalary),
PresentDay = a.PresentDay,
UserName = b.UserName
});
return data;
}
</salarymonthlyviewmodel>