System.ArgumentNullException: '值不能是 null。 参数名称：providerInvariantName'

Question

I'm trying to create a c# application using N- Tier architecture. This is my business layer method to insert a record in database.

public static bool AddEmployeeBL(Employee newEmployee)
        {
            bool employeeAdded = false;
            try
            {
                if(ValidateEmployee(newEmployee))
                {
                    EmployeeDAL employeeDAL = new EmployeeDAL();
                    employeeAdded = employeeDAL.AddEmployeeDAL(newEmployee);
                }
            }
            catch (MyException ex)
            {
                throw ex;
            }
            
catch (Exception ex)
            {
                throw ex;
            }

            return employeeAdded;
        }

The exception occurs at the throw ex statement in last catch block.

The DAL class method is as follows, here's the method to add data.

public bool AddEmployeeDAL(Employee newEmployee)
        {
            bool employeeAdded = false;

        try
        {
            DbCommand command = DataConnection.CreateCommand();
            command.CommandText = "uspAddEmployee";

            DbParameter param = command.CreateParameter();
            param.ParameterName = "@UserId";
            param.DbType = DbType.Int32;
            param.Value = newEmployee.UserId;
            command.Parameters.Add(param);

            param = command.CreateParameter();
            param.ParameterName = "@Name";
            param.DbType = DbType.String;
            param.Value = newEmployee.Name;
            command.Parameters.Add(param);

            int affectedRows = DataConnection.ExecuteNonQueryCommand(command);

            if (affectedRows > 0)
            {
                employeeAdded = true;
            }

        }
        catch (DbException ex)
        {
            string errorMessage = string.Empty;                
                    errorMessage = ex.Message;
            
            throw new MyException(errorMessage);
        }
        return employeeAdded;
    }

The configuration class: public class MyConfiguration

static string providerName;

private static string connectionString;
public static string ConnectionString { get => connectionString; set => connectionString = value; }
public static string ProviderName { get => providerName; set => providerName = value; }

public MyConfiguration()
{
    providerName = ConfigurationManager.ConnectionStrings["Connection"].ProviderName;
    connectionString = ConfigurationManager.ConnectionStrings["Connection"].ConnectionString;
}

}

Answer 1

Just change the public constructor to static, thus it'll fetch the connection details.

static TravelBookingConfiguration()
        {
            providerName = ConfigurationManager.ConnectionStrings["travelBookingConnection"].ProviderName;
            connectionString = ConfigurationManager.ConnectionStrings["travelBookingConnection"].ConnectionString;
        }