You can use ajax with jQuery.
In your view set an event when the state change, like this:
$(document).on('change', '#state_id', function (e) {
// empty the select with previous cities if we have.
$('#cities').empty();
$.ajax({
type: "POST",
dataType: "json",
// actions is a controller
// cities is a method of actions controller
url : "{{ URL::to('actions/cities') }}",
//here we set the data for the post based in our form
data : $('#MyFormID').serialize(),
success:function(data){
if(data.error === 0 ){ // all was ok
for (var i = 0; i < data.cities.length; i++) {
$('#cities').append("<option value='"+data.cities[i].id+"'>"+data.cities[i].city_name+"</option>")
}
}else{
alert(data);
}
},
timeout:10000
});
});
actions/cities controller
//remember, this is a post method
public function postCities(){
// validate
$validator = Validator::make(Input::all(),
array(
'state_id' => 'required|integer'
));
if ($validator->fails()) {
return Response::json(array('error' => 1, 'message' => 'State is required'));
}
//City is your model, I assumes that you pkey is ID and the city name is city_name and your fkey is state_id
$cities = City::where('state_id', '=', Input::get('state_id'))->get();
return Response::json(array('error' => 0, 'cities' => $cities));
}