Generate sequential InvoiceNo based on last database record in ASP.Net using C# and VB.Net

hi alhamd,

Please refer below sample.

HTML

<asp:TextBox runat="server" ID="txtInvoice"></asp:TextBox>

Namespaces

C#

using System.Configuration;
using System.Data.SqlClient;

VB.Net

Imports System.Configuration
Imports System.Data.SqlClient

Code

C#

protected void Page_Load(object sender, EventArgs e)
{
    if (!this.IsPostBack)
    {
        this.VoucherNo();
    }
}

protected void VoucherNo()
{
    string lastInvoice = "";
    string conString = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
    using (SqlConnection con = new SqlConnection(conString))
    {
        using (SqlCommand cmd = new SqlCommand("SELECT MAX(InvoiceNo) FROM PurchaseOrder", con))
        {
            con.Open();
            lastInvoice = Convert.ToString(cmd.ExecuteScalar());
            con.Close();
        }
    }
    if (!string.IsNullOrEmpty(lastInvoice))
    {
        lastInvoice = "PO-" + (Convert.ToInt32(lastInvoice.Split('-')[1]) + 1).ToString();
    }
    else
    {
        lastInvoice = "PO-1";
    }
    txtInvoice.Text = lastInvoice;
}

VB.Net

Protected Sub Page_Load(sender As Object, e As EventArgs) Handles Me.Load
    If Not Me.IsPostBack Then
        Me.VoucherNo()
    End If
End Sub

Protected Sub VoucherNo()
    Dim lastInvoice As String = ""
    Dim conString As String = ConfigurationManager.ConnectionStrings("constr").ConnectionString
    Using con As SqlConnection = New SqlConnection(conString)
        Using cmd As SqlCommand = New SqlCommand("SELECT MAX(InvoiceNo) FROM PurchaseOrder", con)
            con.Open()
            lastInvoice = Convert.ToString(cmd.ExecuteScalar())
            con.Close()
        End Using
    End Using

    If Not String.IsNullOrEmpty(lastInvoice) Then
        lastInvoice = "PO-" & (Convert.ToInt32(lastInvoice.Split("-"c)(1)) + 1).ToString()
    Else
        lastInvoice = "PO-1"
    End If

    txtInvoice.Text = lastInvoice
End Sub

Screenshots