C＃中的SQL DELETE语句

Question

I'm just asking for help.. it doesn't delete the row. .but i didn't encountered any error.. please help me..my code is:

private void btndelete_Click(object sender, EventArgs e)
    {
        if (txtprn.Text == "" || txtdescription.Text == "")
        {
            MessageBox.Show("No selected file to be delete!", 
                            "Delete Data", 
                             MessageBoxButtons.OKCancel,  
                             MessageBoxIcon.Warning);
        }
        else
        {
            DialogResult answer;
            answer = MessageBox.Show("Are you sure you want to delete this record?", 
                                     "Delete Record",
                                      MessageBoxButtons.YesNo,
                                      MessageBoxIcon.Question, 
                                      MessageBoxDefaultButton.Button2);

            if (answer == DialogResult.Yes)
            {
                con.Open();
                com.CommandText = 
                   @"DELETE 
                       FROM tblsupply 
                      WHERE (prnumber = @prnumber AND         
                             description = @description)";

                com.Parameters.Clear();
                com.Parameters.AddWithValue("@prnumber", txtprn.Text);
                com.Parameters.AddWithValue("@description", txtdescription.Text);
                com.ExecuteNonQuery();
                MessageBox.Show("Record Deleted!");
                con.Close();
            }
            ClearFields();
            GridRefresh();
        }
    }

Answer 1

Check the value of output. If it returns a positive number, that many records are deleted successfully. If you get a -1 a rollback occurs, the return value is also -1.

Convert the txtprn to int as it looks like a number and you are passing as string.

com.Parameters.AddWithValue("@prnumber", Convert.ToInt32(txtprn.Text));
com.Parameters.AddWithValue("@description", txtdescription.Text);
var numberOfRowsAffected = com.ExecuteNonQuery();
MessageBox.Show("Record Deleted!"+numberOfRowsAffected );

Answer 2

I was suggesting not to delete a record based on user input. In your case, you should have an identifier that is not editable by user even more hidden value that your application is managing behind the scene. Scenario:

1. User is adding a new record (though GUI)
2. User is saving and the application should create a new id for it. The application.
3. Once loading the saved record, the application will retrieve the id too and save it somewhere behind the scene.
4. Once deleting the record (though GUI), the deletion will be done according to the id and not through the values in the textboxes.

In your current state, note that the deletion may not succeed in case that are spaces for example so you cannot rely on those texts for deletion.

Answer 3

Place this try catch so you'll know the error

 try
    {
    DialogResult answer;
                answer = MessageBox.Show("Are you sure you want to delete this record?", "Delete Record", MessageBoxButtons.YesNo, MessageBoxIcon.Question, MessageBoxDefaultButton.Button2);

                if (answer == DialogResult.Yes)
                {
                    con.Open();
                    com.CommandText = "DELETE FROM tblsupply WHERE (prnumber=@prnumber AND description=@description)";
                    com.Parameters.Clear();
                    com.Parameters.AddWithValue("@prnumber", txtprn.Text);
                    com.Parameters.AddWithValue("@description", txtdescription.Text);
                    com.ExecuteNonQuery();
                    MessageBox.Show("Record Deleted!");
                    con.Close();
                }
                ClearFields();
                GridRefresh();
    }
    catch(Exception ex)
    {
      ex.Message.ToString();
    }