Three-Tier Architecture: Get All Data and Validations

Question

The project I am working is 'University Management System' and it's a big one. Right now, I am implementing the student registration section that works fine (A small portion of the project). I've used 'Three-Tier Architecture' and 'ORM - EF' in ASP.NET MVC template. In the project, I need to do some validations for registering students depending upon their year, department etc. So there are sections like DAL, BLL, finally controller and view. I've done the validations in the controller and getting the data from BLL that again retrieves data from DAL (This is the simple condition of 'Three-Tier Architecture'). So my questions are:

1) Is it OK to do the validations in the controller?

2) If not and need to do it in the BLL, will it be just fine and why or I can continue doing it in the controller?

Note: To me, doing the validations in the controller or BLL seems OK and the same. Does it have any effect?

Right now, I've done the following:

DAL:

public List<Student> Add(int studentID, string studentName, string email, DateTime regDate)
{
     List<Student> lst = null;
     Student aStudent = new Student();

     aStudent.StudentID = studentID;
     aStudent.StudentName = studentName;
     aStudent.Email = email;
     aStudent.RegDate = regDate;

     try
     {
        db.Students.Add(aStudent);
        db.SaveChanges();
     }

     catch (Exception ex)
     {
        ex.ToString();
     }

    return lst;
 }

BLL:

public List<Student> Add(int studentID, string studentName, string email, DateTime regDate)
{
   return aStudentGateway.Add(studentID, studentName, email, regDate);
}

Controller:

/**Student Registration - Starts**/
[HttpPost]
public ActionResult AddStudent(Student aStudent)
{
    List<Department> departments = aDepartmentManager.GetAllDepartments();
    List<DepartmentViewModel> departmentsViewModel = aDepartmentManager.GetAllDepartmentViewModel();

    DateTime yearInDateTime = Convert.ToDateTime(Request.Form["RegDate"]);
    string extractYear = yearInDateTime.ToString();
    var year = DateTime.Parse(extractYear).Year;
    int department = Convert.ToInt32(Request.Form["Department"]);

    List<Student> studentList = aStudentManager.GetAllStudents();

    int count = 1;

    var query = (from c in studentList
                 where c.Department == department && c.Year == year
                 select c).ToList();

    foreach (var c in query)
    {
        if (query.Count() > 0)
        {
            int m = Convert.ToInt32(c.StudentID);
            count = m + 1; //Incrementing the numbers by one with the table column
        }
        else
        {
            int m = 1;
            count = m + 1; //Incrementing the numbers by one with the variable assigned one
        }
    }

    Student student = new Student();
    student.StudentName = Request.Form["StudentName"];
    student.Email = Request.Form["Email"];
    student.RegDate = Convert.ToDateTime(Request.Form["RegDate"]);
    student.StudentID = count;

    if (aStudentManager.ExistEmailAny(student.Email))
    {
        ViewBag.ErrorMessage = "Email already exists";
    }
    else
    {
        aStudentManager.Add(aStudent.StudentID, aStudent.StudentName, aStudent.Email, aStudent.RegDate);
        ViewBag.Message = "Registration successful. See below to verify.";

        /**This section used to show student details after registration**/
        var result = (from c in departments
                      join d in departmentsViewModel on c.DepartmentID equals d.DepartmentId
                      where d.DepartmentId == department
                      select c);

        foreach (var items in result)
        {
            if (count.ToString().Length > 1)
            {
                ViewBag.StudentID = items.Code + "-" + year + "-" + "0" + count;
            }
            else
            {
                ViewBag.StudentID = items.Code + "-" + year + "-" + "00" + count;
            }

            StudentViewModel.StudentID = student.StudentID;
            StudentViewModel.StudentName = student.StudentName;
            StudentViewModel.Email = student.Email;
            StudentViewModel.RegDate = student.RegDate;
        }
        /**This section used to show student details after registration**/
    }

    return View();
}
/**Student Registration - Ends**/

Answer 1

I would provide multiple steps of validation in the different layers, depending on the context and the meaning of the layer.

First, it's a best practice to provide validation both on client and server side.

For the client side you should provide field checks for required fields and other simple validations. If you are using MVC you can use data annotations.

The same validation should be replicated in the controller. Here you should fail fast applying some kind of contract to the parameters that have been passed. One good practice is using Code Contracts that provide preconditions that need to be satisfied to go on in your pipeline of execution.

In the business layer provide the check that needs to be done in the business logic.

Finally in the data access layer provide all the checks that are needed to persist your data. If you are using EF a good practice is implementing the IValidatableObject for your entity classes. Here in Scott Gu's blog you can find a post that explains this technique.

Even though this approach look like it will introduce repetitions, it will provide consistency in your data and separate concerns between your layers.