Populate DropDownList from another DropDownList

Question

I have two related models.

public partial class bs_delivery_type
{  
    public decimal delivery_id { get; set; }
    public decimal delivery_city_id { get; set; }
    public string delivery_address { get; set; }

    public virtual bs_cities bs_cities { get; set; }
}

and the second one:

public partial class bs_cities
{
    public bs_cities()
    {
        this.bs_delivery_type = new HashSet<bs_delivery_type>();
    }

    public decimal cities_id { get; set; }
    public string cities_name { get; set; }

    public virtual ICollection<bs_delivery_type> bs_delivery_type { get; set; }
}

and I have such ViewBag's for dropdownlist's:

ViewBag.city = new SelectList(_db.bs_cities, "cities_id", "cities_id");
ViewBag.delivery_adress = new SelectList(_db.bs_cities, "delivery_id", "delivery_address");

When I choose city in first dropdownlist, in the second one there has to be appeared binded list with delivery_adress , where delivery_city_id = cities_id (from first dropdownlist).

How to do that?

Edit: I tryed method from @Izzy's comment, so here is my actual view:

@model Bike_Store.Models.DeliveryModel

@{
ViewBag.Title = "Checkout";
}
<script src="~/Scripts/bootstrap.min.js"></script>
<script src="~/Scripts/jquery-3.1.1.min.js"></script>


<script src="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8/jquery-ui.min.js"></script>
<script type="text/javascript">
function GetDelivery(_stateId) {
    var procemessage = "<option value='0'> Please wait...</option>";
    $("#ddldelivery").html(procemessage).show();
    var url = "/Shop/GetDeliveryByCityId/";

    $.ajax({
        url: url,
        data: { cities_id: _stateId },
        cache: false,
        type: "POST",
        success: function (data) {
            var markup = "<option value='0'>Select adress</option>";
            for (var x = 0; x < data.length; x++) {
                markup += "<option value=" + data[x].Value + ">" + data[x].Text + "</option>";
            }
            $("#ddldelivery").html(markup).show();
        },
        error: function (reponse) {
            alert("error : " + reponse);
        }
    });

}
</script>
<h2>Checkout</h2>
@using (Html.BeginForm())
{
@Html.DropDownListFor(m=>m.CitiesModel, new SelectList(Model.CitiesModel, "cities_id", "cities_name"), new {@id = "ddldelivery", @style="width:200px", @onchange="javascript:GetDelivery(this.value);"})
<br />
<br />
<select id="ddldelivery" name="ddldelivery" style="width:200px">

</select>
<br /><br />

}

My controller now looks like this:

public List<bs_cities> GetAllCities()
    {
        List<bs_cities> cities = new List<bs_cities>();
        foreach (var city in _db.bs_cities)
        {
            cities.Add(city);
        }
        return cities;
    }

    public List<bs_delivery_type> GetAllDeliveries()
    {
        List<bs_delivery_type> deliveries = new List<bs_delivery_type>();
        foreach (var delivery in _db.bs_delivery_type)
        {
            deliveries.Add(delivery);
        }
        return deliveries;
    }

    [HttpPost]
    public ActionResult GetDeliveryByCityId(decimal cities_id)
    {
        List<bs_delivery_type> delivery = new List<bs_delivery_type>();
        delivery = GetAllDeliveries().Where(m => m.delivery_city_id == cities_id).ToList();
        SelectList objDelivery = new SelectList(delivery, "delivery_id", "delivery_address", 0);
        return Json(objDelivery);
    }

    public ViewResult Checkout()
    {
        DeliveryModel deliveryModel = new DeliveryModel();
        deliveryModel.CitiesModel = new List<bs_cities>();
        deliveryModel.CitiesModel = GetAllCities();
        return View(deliveryModel);
    }

The problem now is that i have 2 ddls, but works only first one. In scrshot you can see I have a list of cities, when I choose a city, in this same ddl appears a list of delivery adresses, and when I choose adress - its desappears. What a magic? Help me please with Ajax. List of cities

I guesse i fixed it, the problem was in:

@Html.DropDownListFor(m=>m.CitiesModel, new SelectList(Model.CitiesModel, "cities_id", "cities_name"), new {@id = "ddldelivery", @style="width:200px", @onchange="javascript:GetDelivery(this.value);"})

I changes @id = "ddldelivery" to @id = "ddlcity" and it works now

Answer 1

The following guide will show you:

• Create a partial view
• Takes cityid as input and outputs the delivery address list
• Load partial view into your select

Note: Partial view solution may be overkill in this situation, but for similar problems it is actually quite usefull.

PartialView .cshtml

Filename: _deliveryTypePartial.cshtml

@model List<bs_delivery_type>

@foreach(var item in Model)
{
    <option value="@item.delivery_id">
        @item.delivery_address
    </option>
}

Controller Code for Partial View:

public IActionResult _deliveryTypePartial(decimal city_id)
{
    List<bs_delivery_type> model = context.bs_delivery_types.Where(row => row.delivery_city_id == delivery_city_id).ToList();
    return PartialView(model);
}

And then Finally, for your AJAX

I notice that your two dropdownlists have identical ID's witch will cloud your javascript code and is considered bad practice, so for the purposes of this guide I will call the first dropdownlist:

ddlcity

Now, inside your onchange function for ddlcity :

$('#ddldelivery').load("/ControllerName/_deliveryTypePartial?city_id=" _stateId);

This should load the partial view into your second dropdown list.

PS : As I completed this question you had already used the direct ajax method, I agree that both methods are equally suitable in this case. You can perhaps use the method outlined here if the actual objects you need to populate are a lot more complex.