Oledbdatareader reader = comand.executereader(); error in this line

Question

1.00/5 (1 vote)

See more:

C#

using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Data.OleDb;

namespace practice2
{
    public partial class Form1 : Form
    {
       private OleDbConnection connection = new OleDbConnection();
       
        public Form1()
        {
            InitializeComponent();
             connection.ConnectionString = @"Provider = Microsoft.ACE.OLEDB.12.0; Data Source = C:\Users\Ahmed ch\Documents\Database1.accdb;
            Persist Security Info = False;";
           
        }

      
        private void Form1_Load(object sender, EventArgs e)
        {
           try
            {
            connection.Open();
           
                OleDbCommand comand = new OleDbCommand();
                String query =  "select* from Sheet2"
                comand.CommandText = query;
                OleDbDataReader reader = comand.ExecuteReader();
                while (reader.Read())
                {
                     comboBox1.Items.Add(reader["ProductName"].ToString());
                }


                connection.Close();
               
            }
                catch(Exception ex)
            {
                MessageBox.Show("Error" + ex);
                
            }
           
       
        }}}

What I have tried:

i also install oledb driver , MS Access database Engine X86 , also X64 , but every time error comes ,

C#

OleDbDataReader reader = comand.ExecuteReader();

in this line

Posted 5-Aug-16 6:52am

ahmed ch

Updated 5-Aug-16 11:52am

Patrice T

v2

Add a Solution

Comments

Karthik_Mahalingam 5-Aug-16 12:54pm

what is the error message?

[no name] 5-Aug-16 12:59pm

You forgot to set the Connection to your OleDBCommand.

Btw: I prefer to do it this way: OleDbCommand command = new OleDbCommand(sql, oleDbConnection);

ZurdoDev 5-Aug-16 13:46pm

The error would tell you, and us, exactly what the problem is. Then bingo, problem solved faster than the amount of time it took you to ask. ;)

2 solutions

Solution 2

Two possible problems: one is (as 0x01AA said) that the command is not connected to any database. The other is that you should have a space between "SELECT" and "*" in your SQL command - it's not required, but it's a good idea - particularly as "SELECT *" is considered a bad idea anyway. You should name your columns in the SELECT so that you only fetch the ones you need.
In addition, Commands and Connections are scarce resources, and it's a good idea to use a using block to ensure they are closed and disposed as needed.

C#

try
    {
    using (OleDbConnection con = new OleDbConnection(@"Provider=Microsoft.ACE.OLEDB.12.0; Data Source = C:\Users\Ahmed ch\Documents\Database1.accdb;Persist Security Info = False;";))
        {
        con.Open();
        using (OleDbCommand cmd = new OleDbCommand("SELECT ProductName FROM Sheet2", con))
            {
            using (OleDbDataReader reader = cmd.ExecuteReader())
                {
                while (reader.Read())
                    {
                    comboBox1.Items.Add(reader["ProductName"].ToString());
                    }
                }
            }
        }
    }
catch(Exception ex)
    {
    MessageBox.Show("Error" + ex);
    }

Posted 5-Aug-16 8:11am

OriginalGriff

Comments

[no name] 5-Aug-16 15:02pm

A 5 for all the hints.

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

User 11060979 · Accepted Answer · 2016-08-05T08:09:00

The exception you get is most probably "System.InvalidOperationException: ExecuteReader: Connection property has not been initialized". This because you forgot to set the Connection property of the OleDBCOmmand.

C#

private void Form1_Load(object sender, EventArgs e)
{
  try
  {
    connection.Open();

    OleDbCommand comand = new OleDbCommand();
    String query = "select* from Sheet2"
    comand.CommandText = query;
    comand.Connection = connection;  // <<<< set connection
    OleDbDataReader reader = comand.ExecuteReader();
  // ....
}