How to get the username when they login and store it to database when users clicked vote button

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When the users click the vote button, the candidateID that being displayed in the gridview will be store to the database.However, I want to store who vote for the particular candidate (store they studentID). I'd like capture thier username when they login, and when they click the vote button, insert their studentID to the database

I store the session in the user login page. How can I store it to the database using the insert command(when they click the vote button)?

What I have tried:

<pre><pre lang="c#">
protected void LinkButton_Click(Object sender, EventArgs e)
    {
        String MyConnection2 = "Server=localhost;database=ovs;Uid=root;password=; Convert Zero Datetime=True";
     
        MySqlConnection MyConn2 = new MySqlConnection(MyConnection2);      
        GridViewRow grdrow = (GridViewRow)((LinkButton)sender).NamingContainer;
        Label lblStudentId = (Label)grdrow.Cells[0].FindControl("lblID");
        string studentId = lblStudentId.Text;
        String query = "insert into voting (studentID,)values ('" + lblStudentId.Text + "')";  
        MySqlCommand MyCommand2 = new MySqlCommand(query, MyConn2);
        MySqlDataReader MyReader2;
        MyConn2.Open();
        MyReader2 = MyCommand2.ExecuteReader();

        while (MyReader2.Read())
        {
        }
        MyConn2.Close();
    }

    }

<pre lang="c#">
 Session["UserName"] = txtID.Text;
txtID.Text = Session["UserName"].ToString();

Posted 6-Aug-20 21:58pm

ycwong99

Updated 6-Aug-20 22:07pm

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BillWoodruff 7-Aug-20 10:03am

So much for anonymous voting.

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OriginalGriff · Answer 1 · 2020-08-06T22:07:00

Not like that! Never concatenate strings to build a SQL command. It leaves you wide open to accidental or deliberate SQL Injection attack which can destroy your entire database. Always use Parameterized queries instead.

When you concatenate strings, you cause problems because SQL receives commands like:

SQL

SELECT * FROM MyTable WHERE StreetAddress = 'Baker's Wood'

The quote the user added terminates the string as far as SQL is concerned and you get problems. But it could be worse. If I come along and type this instead: "x';DROP TABLE MyTable;--" Then SQL receives a very different command:

SQL

SELECT * FROM MyTable WHERE StreetAddress = 'x';DROP TABLE MyTable;--'

Which SQL sees as three separate commands:

SQL

SELECT * FROM MyTable WHERE StreetAddress = 'x';

A perfectly valid SELECT

SQL

DROP TABLE MyTable;

A perfectly valid "delete the table" command

SQL

--'

And everything else is a comment.
So it does: selects any matching rows, deletes the table from the DB, and ignores anything else.

So ALWAYS use parameterized queries! Or be prepared to restore your DB from backup frequently. You do take backups regularly, don't you?

In addition, you should never hard code connections strings - always store these in a config file so that you don't have to change them every time you release a new version! And storing them in every method? That's just insane - and a recipe for major problems when you try to fix a bug and find you are working to production DB in a method that deletes the whole DB by accident...
Read it from your config file once, and reuse the string from there.

Then look at fixing the problem you have noticed: take the comma away after "StudentID" in your INSERT command:

C#

string query = "INSERT INTO Voting (StudentID) VALUES ( ... )";