Error: The parameters dictionary contains a null entry for parameter ‘id’ of non-nullable type ‘System.Int32’ for method ‘CumulativeP1.Models.Teacher FindTeacher(Int32)’ in ‘CumulativeP1.Controllers.TeacherDataController’. An optional parameter must be a reference type, a nullable type, or be declared as an optional parameter.

teacherid – int, primary key in SQL.

api controller

 [HttpGet]
 public List<Teacher> ListTeachers()
 {
     // Create an instance of a connection
     MySqlConnection Connection = School.AccessDatabase();

     // Open the connection between the web server and database
     Connection.Open();

     // Establish a new command (query) for our database
     MySqlCommand Command = Connection.CreateCommand();

     //SQL QUERY
     Command.CommandText = "Select * from teachers";

     // Gather Result Set of Query into a variable
     MySqlDataReader ResultSet = Command.ExecuteReader();

     // Create an empty list of Teacher Names
     List<Teacher> Teachers = new List<Teacher>();

     // Loop Through Each Row the Result Set
     while (ResultSet.Read())
     {
         //Access Column innformation by the DB column name as an index
         string TeacherName = ResultSet["teacherfname"] + " " + ResultSet["teacherlname"];
         string EmployeeNumber = Convert.ToString(ResultSet["employeenumber"]);
         decimal TeacherSalary = Convert.ToDecimal(ResultSet["salary"]);
         DateTime TeacherHireDate = Convert.ToDateTime(ResultSet["hiredate"]);


         Teacher NewTeacher = new Teacher();
         NewTeacher.TeacherName= TeacherName;
         NewTeacher.TeacherSalary= TeacherSalary;
         NewTeacher.TeacherHireDate= TeacherHireDate;
         NewTeacher.EmployeeNumber= EmployeeNumber;

         // Add the Teacher elements to the List
         Teachers.Add(NewTeacher);
     }

     // Close the connection between the MySQL Database and the WebServer
     Connection.Close();

     // Return the final list of author names
     return Teachers;

 }

 [HttpGet]
 public Teacher FindTeacher(int id)
 {
     Teacher NewTeacher = new Teacher();

     // Create an instance of a connection
     MySqlConnection Connection = School.AccessDatabase();

     // Open the connection between the web server and database
     Connection.Open();

     // Establish a new command (query) for our database
     MySqlCommand Command = Connection.CreateCommand();

     //SQL QUERY
     Command.CommandText = "SELECT * FROM teachers WHERE teacherid = "+id;

     // Gather Result Set of Query into a variable
     MySqlDataReader ResultSet = Command.ExecuteReader();

     while (ResultSet.Read())
     {
         string TeacherName = ResultSet["teacherfname"] + " " + ResultSet["teacherlname"];
         string EmployeeNumber = Convert.ToString(ResultSet["employeenumber"]);
         decimal TeacherSalary = Convert.ToDecimal(ResultSet["salary"]);
         DateTime TeacherHireDate = Convert.ToDateTime(ResultSet["hiredate"]);


         NewTeacher.TeacherName = TeacherName;
         NewTeacher.TeacherSalary = TeacherSalary;
         NewTeacher.TeacherHireDate = TeacherHireDate;
         NewTeacher.EmployeeNumber = EmployeeNumber;


     }


     return NewTeacher;
 }

my class:

 public class Teacher
 {

     // we use this class to describe what teachers' fields are for other components
     public string TeacherName { get; set; }
     public string EmployeeNumber { get; set; }
     public decimal TeacherSalary { get; set; }
     public DateTime TeacherHireDate { get; set; }
     public int TeacherID { get; set; }

 }

My MVC controller

// GET: teacher/show/{id}
public ActionResult Show(int id)
{   
    TeacherDataController controller = new TeacherDataController();
    Teacher NewTeacher = controller.FindTeacher(id);
    
    return View(NewTeacher);
}

Haven’t started to work on html, very simple now.

@model CumulativeP1.Models.Teacher
@{
    ViewBag.Title = "Show";
}

<h2>Show Teachers</h2>
@Model.TeacherName

I suppose the problem is about teacherid, is my code right in getting SQL data?

Command.CommandText = "SELECT * FROM teachers WHERE teacherid = "+id;

Not sure why the error message indicating null parameter, teacherid is the primary key in the database…