Question

If a user selects a value from an HTML drop down list A, I want to make an ajax call to the server to populate the values in HTML drop down list B based on the user’s selection.

I am using ASP.NET MVC 4 with EF 4. How do I do that?

Answer 1

Listen for the change event of first drop down and then load the content of second drop down in JSON format and inject that to the second drop down

<select id="country">
  <option value='1'>USA</option>
  <option value='2'>Canada</option>
</select>
<select id="States"></select>

and the script

$(function(){
  $("#country").change(function(){
    var _this=$(this);
    var items="";
    $.getJSON("@Url.Action("GetStates","Country")/"+_this.val(),function(data){
           if(data.Status==="Success")
           {
              $.each(data.Items,function(index, item){
                 items=+"<option value='"+item.ID+'">"+item.Name+"</option>";
              });                 
           }
           $("#states").html(items);
    });
  });       
});

Assuming your GetStates action method returns JSON data with ID and Name as below.

public ActionResult GetStates(int id)
{
  List<State> stateList=yourRepositary.GetStatesForCountry(id);
  return Json(new { Status="Success", Items=stateList},
                                           JsonRequestBehaviour.AllowGet);
}

Assuming GetStatesForCountry method returns a list of State object with ID and Name as properties.