Question

When StudentId is passed as a parameter in controller action, how can I validate if the id passed is present in StudentTable in a controller action?

        public ActionResult LookUpStudentId(string id)
    {

        if(id != //not present in StudentTable)
          return new RedirectResult("~/Error/NotFound");


        return View();

    }

Answer 1

The answer to your question will very much depend on the data access technology you are using to access your SQL server. Because you haven’t told us about it here’s how to achieve this using plain ADO.NET:

public bool IsStudentExists(string id)
{
    using (var conn = new SqlConnection("some connection string"))
    using (var cmd = conn.CreateCommand())
    {
        conn.Open();
        cmd.CommandText = "SELECT id FROM StudentTable WHERE id = @id";
        cmd.Parameters.AddWithValue("@id", id);
        using (var reader = cmd.ExecuteReader())
        {
            return reader.Read();
        }
    }
}

and then:

public ActionResult LookUpStudentId(string id)
{
    if(!IsStudentExists(id))
    {
        return new RedirectResult("~/Error/NotFound");
    }
    return View();
}

Obviously this data access code is better to be refactored in a repository so that your controller is not tightly coupled to the data access technology you are using. So for example you would define a IStudentsRepository:

public interface IStudentsRepository
{
    Student GetStudent(string id);
}

which you would then implement and now your controller action could work with this abstraction:

public class StudentsController: Controller
{
    private readonly IStudentsRepository _repository;
    public StudentsController(IStudentsRepository repository)
    {
        _repository = repository;
    }

    public ActionResult LookUpStudentId(string id)
    {
        var student = _repository.GetStudent(id);
        if(student == null)
        {
            return new RedirectResult("~/Error/NotFound");
        }
        return View(student);
    }
}

All that is left is to configure your DI framework of choice to inject the proper implementation of this repository into the controller.