从数据库中读取一列数据到组合框的代码返回操作数据库错误

Question

private void AddStudentForm_Load(object sender, EventArgs e)
        {
            string connString = "Data Source=MICROSOF-200B28\\SQLEXPRESS;Initial Catalog=MySchool;Integrated Security=True ";
            SqlConnection connection = new SqlConnection(connString);
             
            try
            {
                
                string sql = "select GradeName form Grade";
               
                SqlCommand command = new SqlCommand(sql, connection);
                connection.Open();
                MessageBox.Show("连接数据库成功");
                SqlDataReader dataReader = command.ExecuteReader();
                string gradeName = "";
                while (dataReader.Read())
                {
                    gradeName = (string)dataReader[0];
                    cobGrade.Items.Add(gradeName);
                }
                dataReader.Close();
            }
            catch (Exception ex)
            {
                MessageBox.Show("操作数据库出错");
                Console.WriteLine(ex.Message);            }
            finally
            {
                connection.Close();
            }        }

Answer 1

while (dataReader.Read())
之前加上 if(dataReader.hasrows)

Answer 2

cobGrade.Items.Add(dataReader[0].ToString());
看看ex.Message

Answer 3

设在 MessageBox.Show("连接数据库成功");
下面