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Cascading dropdownlists with linq to sql

In this article I am going to explain how to populate Cascading dropdown list using linq to sql

Description:

I want to populate the Country, State and City dropdownlist.

Implementation:
I have created three tables Tb_Country, Tb_State and Tb_City.

Cascading dropdownlists with linq to sql

HTML Markup of webform:
    <table>
    <tr>
    <td>Select Country:</td>
     <td>  <asp:DropDownList ID="ddlcountry" runat="server" AutoPostBack="true"
            onselectedindexchanged="ddlcountry_SelectedIndexChanged">
        </asp:DropDownList></td>
    </tr>
       <tr>
    <td></td>
     <td></td>
    </tr>
     <tr id="state" runat="server">
    <td>Select State:</td>
     <td><asp:DropDownList ID="ddlstate" runat="server" AutoPostBack="true"
            onselectedindexchanged="ddlstate_SelectedIndexChanged">
        </asp:DropDownList></td>
    </tr>
     <tr>
    <td></td>
     <td></td>
    </tr>
     <tr id="city" runat="server">
    <td>Select City:</td>
     <td> <asp:DropDownList ID="ddlcity" runat="server">
        </asp:DropDownList></td>
    </tr>
    </table>

Create object of DBML

C#:
BlogDataContext db = new BlogDataContext();

VB:
Private db As New BlogDataContext()

Bind the country dropdownlist
Write a method to bind the country dropdownlist and call it in page load event.
C# code:


protected void Page_Load(object sender, EventArgs e)
    {
        city.Visible = false;
        state.Visible = false;
        if (!IsPostBack)
        {
            BindCountry();
        }
    } 
    public void BindCountry()
    {
        try
        {
            var country = from co in db.Tb_Countries
                          select co;
            ddlcountry.DataSource = country;
            ddlcountry.DataValueField = "Id";
            ddlcountry.DataTextField = "CountryName";
            ddlcountry.DataBind();
            ddlcountry.Items.Insert(0, new ListItem("--Select--", "0"));
        }
        catch (Exception ex)
        { }
    }

VB code:
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        city.Visible = False
        state.Visible = False
        If Not IsPostBack Then
            BindCountry()
        End If
    End Sub
    Public Sub BindCountry()
        Try
            Dim country = From co In db.Tb_Countries
                          Select co
            ddlcountry.DataSource = country
            ddlcountry.DataValueField = "Id"
            ddlcountry.DataTextField = "CountryName"
            ddlcountry.DataBind()
            ddlcountry.Items.Insert(0, New ListItem("--Select--", "0"))
        Catch ex As Exception
        End Try
    End Sub

Populate the state dropdownlist
On SelectIndexchanged event of country dropdown write the below given code
C# code:
protected void ddlcountry_SelectedIndexChanged(object sender, EventArgs e)
    {
        try
        {
            var state = from st in db.Tb_States
                        where st.CountryId_Fk == ddlcountry.SelectedIndex
                        select st;
            ddlstate.DataSource = state;
            ddlstate.DataValueField = "Id";
            ddlstate.DataTextField = "StateName";
            ddlstate.DataBind();
            ddlstate.Items.Insert(0, new ListItem("--Select--", "0"));           
        }
          
        catch (Exception ex)
        { }
        finally
        {
              state.Visible = true;
        }
    }

VB code:
Protected Sub ddlcountry_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles ddlcountry.SelectedIndexChanged
        Try
            Dim state = From st In db.Tb_States Where st.CountryId_Fk = ddlcountry.SelectedIndex
                        Select st
            ddlstate.DataSource = state
            ddlstate.DataValueField = "Id"
            ddlstate.DataTextField = "StateName"
            ddlstate.DataBind()
            ddlstate.Items.Insert(0, New ListItem("--Select--", "0"))

        Catch ex As Exception
        Finally
            state.Visible = True
        End Try
    End Sub

Populate the city dropdownlist
To SelectIndexchanged event of State dropdown write the below given code
C# code:
protected void ddlstate_SelectedIndexChanged(object sender, EventArgs e)
    {
        try
        {
            var city = from ct in db.Tb_Cities
                        where ct.StateId_Fk == Convert.ToInt32(ddlstate.SelectedValue)
                        select ct;
            ddlcity.DataSource = city;
            ddlcity.DataValueField = "Id";
            ddlcity.DataTextField = "CityName";
            ddlcity.DataBind();
            ddlcity.Items.Insert(0, new ListItem("--Select--", "0"));          
        } 
        catch (Exception ex)
        { }
        finally
        {
            state.Visible = true;
            city.Visible = true;
        }
    }

VB code:
Protected Sub ddlstate_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles ddlstate.SelectedIndexChanged
        Try
            Dim city = From ct In db.Tb_Cities Where ct.StateId_Fk = Convert.ToInt32(ddlstate.SelectedValue)
                       Select ct
            ddlcity.DataSource = city
            ddlcity.DataValueField = "Id"
            ddlcity.DataTextField = "CityName"
            ddlcity.DataBind()
            ddlcity.Items.Insert(0, New ListItem("--Select--", "0"))
        Catch ex As Exception
        Finally
            state.Visible = True
            city.Visible = True
        End Try
    End Sub

Build the project and run

Demo:
Cascading dropdownlists with linq to sql
    In this article we have learn to how to populate the cascading dropdownlist using linq to sql (C#, VB.net)I hope you enjoyed this article.

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