Insert QR into database using C#

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hello guys
well i generated a QR code using zenbarcode for windowforms in c# , but i found difficulties to insert it into the database i connected to my application .
can u help please ?
thanks .

What I have tried:

ImageConverter converter = new ImageConverter();

           converter.ConvertTo(pictureBox1.Image, typeof(byte[]));


           NpgsqlCommand cd = new NpgsqlCommand("insert into donnees_recolte(qr_code) values @qr_code where id_recolte = '"+this.textBox2.Text+"') ", cnx);
           NpgsqlDataAdapter ad = new NpgsqlDataAdapter(cd);
           cd.Parameters.Add(new NpgsqlParameter("@qr_code", converter));
           DataTable dt = new DataTable();
           ad.Fill(dt);
           dataGridView1.DataSource = dt;

           cnx.Open();

but still no result

Posted 22-May-20 16:47pm

MOUAD MOUMENE

Updated 22-May-20 19:45pm

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OriginalGriff · Answer 1 · 2020-05-22T19:46:00

First off, don;t do it 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?

You know what a parameterized query is, so why suddenly start to ignore them?

Second, ImageConverter.ConvertTo doesn't change anything - it returns a new object of the requested type. You need to save that reference, and pass that to your DB, not the ImageConverter instance itself:

C#

ImageConverter converter = new ImageConverter();
byte[] data = (byte[]) converter.ConvertTo(im, typeof(byte[]));
...
cd.Parameters.Add(new NpgsqlParameter("@qr_code", data));

But ... why are you faffing about with a DataAdapter to do an insert, and even trying to use Fill on it? I'm pretty sure that won't do what you want it to ... No SELECT for the DataTable to get any information, no instruction to actually do the INSERT.
Use a Command object with the INSERT instead, and then call ExecuteNonQuery on that.