试图为SQL条目创建一个投票系统(投票人必须有客户编号记录)

我目前正在创建一个投票系统，现有用户可以通过sql数据集表投票决定其他条目是否有效(upvote/Downvote)。

每个注册的用户获得一个客户号，用户需要一个客户号来投票。当用户投票时，他们的客户号被记录在条目中，sql查询更新分数，将upvote加1或downvote加1。对每个已投票条目的投票人ID应用唯一约束，以防止重复投票，并且用户必须有客户编号才能投票。

下面的我的代码尝试这样做，但它似乎总是以消息框结束，说"错误，你不能投票，直到你在文本框中提供一个有效的客户号码"。所有的帮助是感激的，非常感谢!

protected void searchTheDB()
{
    string s = "SELECT compName As 'Company/Organization Name', btcAddr As 'Bitcoin Address', Premium_User as 'Premium User'," + 
    "upvote as 'Upvotes',downvote As 'Downvotes' FROM clientDataTable WHERE compName LIKE '%" + searchBox.Text + "%'";
    try
    {
        SqlConnection forSearch = new SqlConnection(connectionString);
        SqlDataAdapter search = new SqlDataAdapter(s, forSearch);
        DataSet dB = new DataSet();
        search.Fill(dB);
        searchGridView.DataSource = dB;
        searchGridView.DataBind();
        searchBox.Text = String.Empty;
    }
    catch (SqlException exp)
    {
        throw new InvalidOperationException("Sorry, the website is experiencing difficulties, please try again, error: ", exp);
    }
}
protected void searchButton_Click(object sender, EventArgs e)
{
    custVoteTextBox.Text = String.Empty;
    searchTheDB();
    generalLabel.Text = "results displayed below, if nothing is displayed your search returned no results";
}
protected void canUserVote()
{
    submitCustNumButton_Click(new object(), new EventArgs());
    string query = "INSERT INTO dbo.ClientDataTable (custNum) Values (@custNum)";
    try
    {
        SqlConnection checkCustNum = new SqlConnection(connectionString);
        SqlCommand isCustNumbValid = new SqlCommand(query, checkCustNum);
        isCustNumbValid.Parameters.AddWithValue("@custNum", custNumber);
        checkCustNum.Open();
        isCustNumbValid.ExecuteNonQuery();
        checkCustNum.Close();
    }
    catch (SqlException e)
    {
        if (e.Number == 2627) //checks if customer number is registered by activating unique constraint
        {
            canVote = true;
        }
        else //else user is not eligable to vote
        {
            canVote = false;
            MessageBox.Show("invalid customer number, you cannot vote" + e);
        }
    }
}

protected void searchGridView_RowCommand(object sender, GridViewCommandEventArgs e)
{
    canUserVote();//calls this method to check if user is eligable to vote with the given custNum in the textbox
    if (canVote == true && custVoteTextBox.Text.Length == 8) 
    {
        try
        {
            SqlConnection voteDb = new SqlConnection(connectionString);
            {
                switch (e.CommandName)
                {
                    case "Upvote":
                        int index = Convert.ToInt32(e.CommandArgument);
                        GridViewRow selectedRow = searchGridView.Rows[index];
                        string upvoteUpdateQuery = "UPDATE dbo.clientDataTable SET upvote = @upvote WHERE compName = @compName";
                        SqlCommand Upvote = new SqlCommand(upvoteUpdateQuery, voteDb);
                        Upvote.Parameters.AddWithValue("@upvote", "@upvote" + 1);
                        Upvote.Parameters.AddWithValue("@compName", selectedRow.DataItem.Equals("@compName"));
                        string insertQuery = "INSERT INTO dbo.clientDataTable (voted) Values(@voted) WHERE compName = @compName";
                        SqlCommand insertVoterDetailsUpvote = new SqlCommand(insertQuery, voteDb); //inserts voter information into specific entries table
                        insertVoterDetailsUpvote.Parameters.AddWithValue("@voted", custNumber);
                        insertVoterDetailsUpvote.Parameters.AddWithValue("@compName", selectedRow.DataItem.Equals("compName"));
                        voteDb.Open();
                        Upvote.ExecuteNonQuery();
                        voteDb.Close();
                        break;

                    case "Downvote":
                        int downvoteindex = Convert.ToInt32(e.CommandArgument);
                        GridViewRow downvoteSelectedRow = searchGridView.Rows[downvoteindex];
                        string downvoteUpdateQuery = "UPDATE dbo.clientDataTable SET downvote = @downvote WHERE compName = @compName";
                        SqlCommand Downvote = new SqlCommand(downvoteUpdateQuery, voteDb);
                        Downvote.Parameters.AddWithValue("@downvote", "@downvote" + 1);
                        Downvote.Parameters.AddWithValue("@compName", downvoteSelectedRow.DataItem.Equals("@compName"));
                        string downvoteInsertQuery = "UPDATE clientDataTable SET downvote = downvote + 1 WHERE compName = @compName";
                        SqlCommand insertVoterDetailsDownvote = new SqlCommand(downvoteInsertQuery, voteDb); //inserts voter information into specific entries table
                        insertVoterDetailsDownvote.Parameters.AddWithValue("@voted", custNumber);
                        insertVoterDetailsDownvote.Parameters.AddWithValue("@compName", downvoteSelectedRow.DataItem.Equals("@compName"));
                        voteDb.Open();
                        Downvote.ExecuteNonQuery();
                        voteDb.Close();
                        break;
            }
        }
        }
        catch (SqlException exp)
        {
            if (exp.Number == 2627)
            {
                MessageBox.Show("Sorry, you have already voted");
            }
            else
            {
                throw new InvalidOperationException("Sorry, the website is experiencing difficulties, please try again, error: ", exp);
            }
        }
    }
    else
    {
        MessageBox.Show("error, invalid customer number in the Textbox");
    }
}
protected void submitCustNumButton_Click(object sender, EventArgs e)
{
    int custNo = int.Parse(custVoteTextBox.Text);
    this.custNumber = custNo;
}

if (canVote == true && custNumber.ToString().Length == 9)

if (canVote == true && custNumber.Text.Length == 9)