C# executereader error in mysql data displayig to textboxes

Question

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I can't finish my homework. I get an error by this line:

C#

dr = cmd.ExecuteReader();

That is my source code. How do I fix this error?

C#

MySqlDataReader dr;
private void findData_btn_Click(object sender, EventArgs e)
{
    db_connection();
    cmd = new MySqlCommand("Select * from googolplex.person where Name='" + name_txt.Text + "'", connect);
    dr = cmd.ExecuteReader();
    if (dr.Read())
    {
        try
        {
            name_txt.Text = dr["Name"].ToString();
            surname_txt.Text = dr["Surname"].ToString();
            age_txt.Text = dr["Age"].ToString();
            country_txt.Text = dr["Country"].ToString();
            job_txt.Text = dr["Job"].ToString();
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.Message);
        }
    }
}

What I have tried:

C#

MySqlCommand mcd;
MySqlDataReader mdr;
string s;
private void findData_btn_Click(object sender, EventArgs e)
{
    try
    {
        s = "select * from googolplex.person where id=" + findData_txt.Text;
        mcd = new MySqlCommand(s, connect);
        mdr = mcd.ExecuteReader();
        if (mdr.Read())
        {
            name_txt.Text = mdr.GetString("Name");
            surname_txt.Text = mdr.GetString("Surname");
            age_txt.Text = mdr.GetString("Age");
            country_txt.Text = mdr.GetString("Country");
            job_txt.Text = mdr.GetString("Job");
        }
        else
        {
            MessageBox.Show("Query is failed.","ERROR", MessageBoxButtons.OK, MessageBoxIcon.Error);
        }
    }
    catch (Exception ex)
    {
        MessageBox.Show(ex.Message);
    }
}

Posted 29-Apr-16 10:53am

naperva

Updated 30-Apr-16 17:47pm

VR Karthikeyan

v3

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Comments

Herman<T>.Instance 29-Apr-16 16:58pm

set the try{
before cmd =

naperva 29-Apr-16 17:06pm

Which? MySqlCommand or directly set to execute?

Herman<T>.Instance 29-Apr-16 17:00pm

what error do you get?

naperva 29-Apr-16 17:05pm

It's left to give error. When I click the button nothing change.

Herman<T>.Instance 29-Apr-16 17:11pm

do you understand anything of c# or programming in general?

Dave Kreskowiak 29-Apr-16 17:52pm

And the error would be......???? Hint: The most important piece of information you can have to troubleshoot the problem.

Gautham Prabhu K 30-Apr-16 3:21am

What is the error your getting?

Your homework is to help you learn if you seek professional help for silly issues how do you expect to become a better programmer? If your planning to become one that is!!

naperva 30-Apr-16 20:22pm

An unhandled exception of type 'MySql.Data.MySqlClient.MySqlException' occurred in MySql.Data.dll

Additional information: There is already an open DataReader associated with this Connection which must be closed first.

Rafael Nicoletti 2-May-16 15:38pm

OK, the error by itself tell's what's happening. You clicked and then clicked again.

You need to close/dispose all "external resources":

mdr.Close();
mdr.Dispose();
cmd.Dispose();

The code above isn't the best way to write code. Optimally you should use Dispose pattern by using "using keyword" or dispose/close your resources in the "finally" portion of your try/catch statements.

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George Jonsson · Answer 1 · 2016-04-29T21:53:00

You have not provided enough information to get any useful help.
(You might have figured that out yourself from the comments)

You need to realize that no one can execute your code. We don't know which database your are using in the first place.
Therefor, leaving out crucial information like where the variable connect is declared and initialized doesn't make it easy to give a good answer. (might it be db_connect?)

You also need to provide the error message you get, if any, otherwise it is impossible to help you figure out what is going wrong.

In order to solve your problem you need to use the debugger and set a break point at the first line in the method.

Then you step through the code and see what happens with your variables and statements.

1. The first thing I would check is to see if the variable connect has a value != null.
2. Then you need to make sure that your SQL statement actually gives back any result.
(is the statement if (dr.Read()) ever entered.

At last.
It is always bad to use concatenated SQL commands, due to the vulnerability to SQL injection attacks. See SQL injection - Wikipedia, the free encyclopedia[^]

Use parameterized queries instead. See for example MySQL :: MySQL Connector/Net Developer Guide :: 5.9.1 Preparing Statements in Connector/Net[^]

Midi_Mick · Answer 2 · 2016-04-30T17:47:00

As per your "Additional Information" in the comments -

Most DBMS do not allow multiple data readers to be opened on a single connection at the same time. MySQL and SQLServer does allow it, but the connection needs be established with the "multipleactiveresultsets=true" statement as part of the connection string.

Personally I tend to create a clone of the original connection if I need this functionality. It is more reliable and less prone to error. It also allows for actions being performed on a different thread.

C#

using (MySqlConnection connection2 = (MySqlConnection)connection.Clone()) {
    //... all your stuff using 'connection2' instead of 'connection'
}

C# executereader error in mysql data displayig to textboxes

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