Problem with datareader

Question

0.00/5 (No votes)

See more:

I am working with a windows form in C#. I am using a datareader to populate a listbox. However, I get a message when I ExecuteReader "No value given for one or more required parameters". But I can't find anything wrong. Can you point me in the right direction? Here is the relevant code.

private void loaddata()
        {
            OleDbConnection cn = new OleDbConnection();
            
            cn.ConnectionString = @"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\Access Stuff\ASME_Plate.accdb;Persist Security Info = False;";
            string q = "SELECT DISTINCT [Spec_No] FROM ASME_Plate";
            OleDbCommand cmd = new OleDbCommand(q, cn);
            lstSpec.Items.Clear();
            try
            {
                cn.Open();               
  Error on this line              OleDbDataReader dr = cmd.ExecuteReader();
                MessageBox.Show("OK");
                if (dr.HasRows)
                {
                    while (dr.Read())
                    {

What I have tried:

I tried much code change without success.

Posted 8-May-22 11:19am

BobbyStrain

Updated 13-May-22 22:21pm

Rajeev Jayaram

v3

Add a Solution

Comments

RedDk 8-May-22 17:47pm

I suggest you use VS Object Browser to identify valid/referenced procedures and methods and functions then select a corresponding structure in your code (because it wouldn't make much sense to look for something that doesn't exist as such in the documentation) and give it the old F1 to bring up the HELP.

The documents are riddled with sample/example ... and there's no way to get it wrong copying the same style or at least starting with what is right AND WORKS.

BobbyStrain 8-May-22 21:43pm

RedDk,
I followed your advice. The same notice appears. The ExecuteReader() seem to still be looking for a parameter. It seem there are three overloads, and I tried one to no avail. I'll keep looking It seems like a simple operation to be so troublesome.

Richard MacCutchan 9-May-22 4:09am

Please show the actual message and which line it occurs on.

BobbyStrain 9-May-22 12:13pm

OK. I updated to show the message and where the error occurs. Closing the message, the code continues to execute properly, except for the rest of this method.

Richard MacCutchan 9-May-22 12:36pm

I have tried the same sequence of instructions and cannot get it to fail. There is something wrong with your application that we cannot see.

BobbyStrain 10-May-22 10:25am

I think I will give up the effort. I moved the project to VS 2019 on my laptop with the same result.

BobbyStrain 9-May-22 12:55pm

Everything works except for this one method to populate a listbox. I noted some strange behavior with the connection string. \ was somehow interpreted as an escape sequence and flagged. I undid a number of changes to get it fixed. I'll move the project over to my laptop with VS 2019 and see what happens. Thank you for your help[.

Richard MacCutchan 10-May-22 11:01am

There is definitely something wrong in your application, that we cannot see. I have again recreated your above code exactly, and it works fine. You need to check that you do not have some other definition of ExecuteReader that is being found by the compiler.

BobbyStrain 10-May-22 21:26pm

I have a dataset in the project, but no other reference to a datareader. I populated the list from the datagridview. Took about 5 minutes to code it. Mostly copy & paste.

Richard MacCutchan 11-May-22 3:30am

Well, I am afraid I am out of ideas on this. As I said above, I have created a test which is line for line the same as your code (including the connection string) and it works fine. The only way forward would be for us to see the complete code, although analysis of it may take some considerable time.

BobbyStrain 11-May-22 12:17pm

Well, this was mostly an exercise to use the datareader, which I have not previously used. I am ready to move to another project. Maybe I'll try it again with another project. If you have any interest in resolving the issue, I can send you the whole project somehow.

Richard MacCutchan 11-May-22 12:50pm

It really depends how big it is, I guess. But I would certainly be interested to find out exactly why this is happening.

BobbyStrain 11-May-22 13:03pm

It's pretty small. A datagridview to an small access database. How do I get it to you? You can email me at Bobby@bobby-strain-group.com. I think I still have an account on Media Fire.

Richard MacCutchan 12-May-22 4:30am

As mentioned, if you can post it somewhere that I can download it.

Richard MacCutchan 13-May-22 7:14am

Oops! :)

Maciej Los 9-May-22 15:23pm

Try to move your database into different folder, for example into MyDocuments. Then run VS with admin privileges.

1 solution

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)

Richard MacCutchan · Answer 1 · 2022-05-13T22:21:00

Solution 1

The problem arose due to a mis-spelled table name. The exception message from OLEDB did not help.

Posted 13-May-22 22:21pm

Richard MacCutchan

Comments

Maciej Los 14-May-22 14:19pm

5ed!