传递一个空值

Question

Any suggestions would be awesome!

I keep getting a null value for my ClassID. When I add breakpoints, I can see the value ClassID being passed correctly, but when my program goes back to get a list I created, the ClassID returns null after stepping into that particular breakpoint. I believe my issue is in my controller, but I cant seem to find the issue.

Here is my DB file. The first dataset retrieves my ClassID from a stored procedure and my list below that returns the students in a particular ClassID

public DataSet GetClass(string ClassID)

    {
        ClassModel classes = new ClassModel();
        SqlCommand com = new SqlCommand("sp_ABEAttendanceEnrollment", ABEAttendanceDB);
        com.CommandType = CommandType.StoredProcedure;
        com.Parameters.AddWithValue("@ClassID", ClassID);
        SqlDataAdapter da = new SqlDataAdapter(com);
        DataSet ds1 = new DataSet();
        da.Fill(ds1);
        return ds1;
    }
    public IEnumerable<ClassModel> ClassModel
    {
        get
        {
            string connectionString = ConfigurationManager.ConnectionStrings["ABEAttendanceDB"].ConnectionString;
            List<ClassModel> students = new List<ClassModel>();
            using (SqlConnection con = new SqlConnection(connectionString))
            {
                ClassModel classes = new ClassModel();
                SqlCommand cmd = new SqlCommand("sp_ABEAttendanceEnrollment", ABEAttendanceDB);
                cmd.CommandType = CommandType.StoredProcedure;
                cmd.Parameters.AddWithValue("@ClassID", classes.ClassID);
                SqlDataAdapter da = new SqlDataAdapter(cmd);
                DataSet ds1 = new DataSet();
                da.Fill(ds1);
                ABEAttendanceDB.Open();
                SqlDataReader rdr = cmd.ExecuteReader();
                while (rdr.Read())
                {
                    ClassModel student = new ClassModel();

                    student.ClassID = rdr["ClassID"].ToString();
                    student.SID = rdr["SID"].ToString();
                    student.FullName = rdr["FullName"].ToString();
                    students.Add(student);
                }
                ABEAttendanceDB.Close();
                return students;
            }
        }

    }

Here is my controller

public class ClassController : Controller
{

    DAL.DB dblayer = new DAL.DB();

    public ActionResult Class(ClassModel ClassModel)
    {

        DataSet ds1 = dblayer.GetClass(ClassModel.ClassID);
        ViewBag.general = ds1.Tables;

        ViewBag.Message = TempData["Message"];
        DB classes = new DB();
        List<ClassModel> students = dblayer.ClassModel.ToList();

        return View();
    }


}   

Answer 1

Your DAL code is bit strange. Surely the GetClass method should return the IEnumerable<ClassModel> ? Otherwise it just looks like you end up executing sp_ABEAttendanceEnrollment twice for no real reason. Putting a SQL query in a getter is rather unusual, to say the least. It's also not clear why you would need two copies of your data (one as a collection of DataTable via ViewBag.general and one as a List<ClassModel> via the students variable.

I'm not sure you need the ClassModel property on your DAL class at all. Just make the GetClass method read the data into an IEnumerable<Class> directly, and return it to the controller. Then you can return the list of students to the controller as the model for your view, something like this:

DAL:

public List<ClassModel> GetClass(string ClassID)
{
    List<ClassModel> students = new List<ClassModel>();
    SqlCommand cmd = new SqlCommand("sp_ABEAttendanceEnrollment", ABEAttendanceDB);
    cmd.CommandType = CommandType.StoredProcedure;
    cmd.Parameters.AddWithValue("@ClassID", ClassID);
    ABEAttendanceDB.Open();
    SqlDataReader rdr = cmd.ExecuteReader();

    while (rdr.Read())
    {
        ClassModel student = new ClassModel();
        student.ClassID = rdr["ClassID"].ToString();
        student.SID = rdr["SID"].ToString();
        student.FullName = rdr["FullName"].ToString();
        students.Add(student);
    }

    ABEAttendanceDB.Close();
    return students;
}

Controller:

public class ClassController : Controller
{
    DAL.DB dblayer = new DAL.DB();

    public ActionResult Class(ClassModel ClassModel)
    {
        ViewBag.Message = TempData["Message"];
        List<ClassModel> students = dblayer.getClass(ClassModel.ClassID);

        return View(students);
    }
}

The view would then start with:

@model List<ClassModel>