This article shows how to work with a cascading dropdown list for country/state/city in ASP.Net using Entity Framework.

Create three tables as needed, as in:

  1. CREATE TABLE country
  2. (
  3. countryID INT NOT NULL,
  4. countryName varchar(50) NOT NULL,
  5. PRIMARY KEY (countryID ),
  6. );
  7. CREATE TABLE state
  8. (
  9. stateID INT NOT NULL,
  10. countryID INT NOTNULL,
  11. stateName varchar(50) NOT NULL,
  12. PRIMARY KEY (stateID ),
  13. FOREIGN KEY (countryID ) REFERENCES country (countryID));
  15. CREATE TABLE city
  16. (
  17. cityID INT NOT NULL,
  18. stateID INT NOTNULL,
  19. cityName varchar(50) NOT NULL,
  20. PRIMARY KEY (cityID),
  21. FOREIGN KEY (stateID) REFERENCES state (stateID));

First create an empty web application, as in:

Image1.jpg

Add a model as we did earlier and do the necessary

Image2.jpg

Image3.jpg

Add a web page to the solution and copy and paste this into the .aspx page:

  1. <%@ Page Language="C#" AutoEventWireup="true" CodeBehind="cascading.aspx.cs" Inherits="counrtybasedropdown.cascading" %>
  2. <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
  3. <html xmlns="http://www.w3.org/1999/xhtml">
  4. <head id="Head1" runat="server">
  5. <title></title>
  6. </head>
  7. <body>
  8. <form id="form1" runat="server">
  9. <div>
  10. <center>
  11. <h3>
  12. Cascading DropDownList for Country/State/City in ASP.Net</h3>
  13. <table>
  14. <tr>
  15. <td>
  16. Select a Country :
  17. </td>
  18. <td>
  19. <asp:DropDownList ID="ddlCountry" runat="server" AutoPostBack="true" OnSelectedIndexChanged="ddlCountry_SelectedIndexChanged">
  20. </asp:DropDownList>
  21. </td>
  22. </tr>
  23. <tr>
  24. <td>
  25. Select a State :
  26. </td>
  27. <td>
  28. <asp:DropDownList ID="ddlState" runat="server" Enabled="false" AutoPostBack="true" OnSelectedIndexChanged="ddlState_SelectedIndexChanged">
  29. </asp:DropDownList>
  30. </td>
  31. </tr>
  32. <tr>
  33. <td>
  34. Select a City :
  35. </td>
  36. <td>
  37. <asp:DropDownList ID="ddlCity" runat="server" Enabled="false">
  38. </asp:DropDownList>
  39. </td>
  40. </tr>
  41. </table>
  42. </center>
  43. </div>
  44. </form>
  45. </body>
  46. </html>

Your .aspx.cs should be as follows:

  1. using System;
  2. using System.Collections.Generic;
  3. using System.Linq;
  4. using System.Web;
  5. using System.Web.UI;
  6. using System.Web.UI.WebControls;
  7. namespace counrtybasedropdown
  8. {
  9. public partial class cascading : System.Web.UI.Page
  10. {
  11. Database1Entities dbEntity = new Database1Entities();
  12. protected void Page_Load(object sender, EventArgs e)
  13. {
  14. if (!IsPostBack)
  15. {
  16. var country = from c in dbEntity.countries select new { c.countryID, c.countryName };
  17. ddlCountry.DataSource = country.ToList();
  18. ddlCountry.DataValueField = "countryID";
  19. ddlCountry.DataTextField = "countryName";
  20. ddlCountry.DataBind();
  21. ddlCountry.Items.Insert(0, "--Select--");
  22. }
  23. }
  24. protected void ddlCountry_SelectedIndexChanged(object sender, EventArgs e)
  25. {
  26. int countyID = Convert.ToInt16(ddlCountry.SelectedValue.ToString());
  27. var state = from s in dbEntity.states where s.countryID.Equals(countyID) select new { s.stateID, s.stateName };
  28. ddlState.DataSource = state.ToList();
  29. ddlState.Enabled = true;
  30. ddlState.DataValueField = "stateID";
  31. ddlState.DataTextField = "stateName";
  32. ddlState.DataBind();
  33. ddlState.Items.Insert(0, "--Select--");
  34. }
  35. protected void ddlState_SelectedIndexChanged(object sender, EventArgs e)
  36. {
  37. int stateID = Convert.ToInt16(ddlState.SelectedValue.ToString());
  38. var city = from c in dbEntity.cities where c.stateID.Equals(stateID) select new { c.cityID, c.cityName };
  39. ddlCity.DataSource = city.ToList();
  40. ddlCity.Enabled = true;
  41. ddlCity.DataValueField = "cityID";
  42. ddlCity.DataTextField = "cityName";
  43. ddlCity.DataBind();
  44. ddlCity.Items.Insert(0, "--Select--");
  45. }
  46. }
  47. }

Happy coding.