Display data in TextBox from database on ASP.Net DropDownList selection using jQuery Ajax

Hi Dedzil,

Please refer below sample.

Database

I have made use of the following table Customers with the schema as follows. 

I have already inserted few records in the table.

You can download the database table SQL by clicking the download link below.

Download SQL file

HTML

<asp:DropDownList ID="ddlCountries" runat="server"></asp:DropDownList>
<asp:TextBox ID="txtOther" runat="server" />
<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>
<script type="text/javascript">
    $(function () {
        $("[id*=ddlCountries]").on('change', function () {
            var country = $("[id*=ddlCountries]").find("option:selected").text();
            $.ajax({
                type: "POST",
                url: "Default.aspx/GetData",
                data: "{country:'" + country + "'}",
                contentType: "application/json; charset=utf-8",
                dataType: "json",
                success: function (data) {
                    $('[id*=txtOther]').val(data.d.Name);
                },
                error: function (response) {
                    alert(response.responseText)
                }
            });
        });
    });
</script>

Namespaces

C#

using System.Data;
using System.Data.SqlClient;
using System.Configuration;
using System.Web.Services;

VB.Net

Imports System.Data
Imports System.Data.SqlClient
Imports System.Configuration
Imports System.Web.Services

Code

C#

protected void Page_Load(object sender, EventArgs e)
{
    if (!this.IsPostBack)
    {
        string conString = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
        using (SqlConnection con = new SqlConnection(conString))
        {
            using (SqlCommand cmd = new SqlCommand("SELECT Country FROM Customers", con))
            {
                con.Open();
                ddlCountries.DataSource = cmd.ExecuteReader();
                ddlCountries.DataTextField = "Country";
                ddlCountries.DataValueField = "Country";
                ddlCountries.DataBind();
                con.Close();
            }
        }
    }
}

[WebMethod]
public static object GetData(string country)
{
    string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
    using (SqlConnection con = new SqlConnection(constr))
    {
        string query = "SELECT * FROM Customers WHERE Country = @Country";
        using (SqlCommand cmd = new SqlCommand(query))
        {
            cmd.Connection = con;
            cmd.Parameters.Add("@Country", SqlDbType.VarChar).Value = country;
            con.Open();
            SqlDataReader sdr = cmd.ExecuteReader();
            if (sdr.Read())
            {
                return new { Name = sdr["Name"], Id = sdr["CustomerId"] };
            }
            con.Close();
        }

        return null;
    }
}

VB.Net

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
    If Not Me.IsPostBack Then
        Dim conString As String = ConfigurationManager.ConnectionStrings("constr").ConnectionString
        Using con As SqlConnection = New SqlConnection(conString)
            Using cmd As SqlCommand = New SqlCommand("SELECT Country FROM Customers", con)
                con.Open()
                ddlCountries.DataSource = cmd.ExecuteReader()
                ddlCountries.DataTextField = "Country"
                ddlCountries.DataValueField = "Country"
                ddlCountries.DataBind()
                con.Close()
            End Using
        End Using
    End If
End Sub

<WebMethod>
Public Shared Function GetData(ByVal country As String) As Object
    Dim constr As String = ConfigurationManager.ConnectionStrings("constr").ConnectionString
    Using con As SqlConnection = New SqlConnection(constr)
        Dim query As String = "SELECT * FROM Customers WHERE Country = @Country"
        Using cmd As SqlCommand = New SqlCommand(query)
            cmd.Connection = con
            cmd.Parameters.Add("@Country", SqlDbType.VarChar).Value = country
            con.Open()
            Dim sdr As SqlDataReader = cmd.ExecuteReader()

            If sdr.Read() Then
                Return New With {
                .Name = sdr("Name"),
                .Id = sdr("CustomerId")
            }
            End If

            con.Close()
        End Using

        Return Nothing
    End Using
End Function

Screenshot