[Answered ]-How to set dynamic mapping between two models in django

You achieve this using jQuery and Ajax. Try using the following:

project_change.js

(function($){   
    $(function(){
        $(document).ready(function() {
            $('#id_Project').bind('change', project_change);            
            $('#id_Milestone > option').show();
            if ($('#id_Project').val() != '') {
                var project_id = $('#id_Project').val();
                $.ajax({
                "type"      : "GET",
              "url"         : "/product_change/?project_id="+project_id,
                "dataType"  : "json",
              "cache"       : false,
                "success"   : function(json) {
                    $('#id_Milestone >option').remove();
                    for(var j = 0; j < json.length; j++){
                        $('#id_Milestone').append($('<option></option>').val(json[j][0]).html(json[j][1]));
                    }
                }           
            });
            }
        });
    });  
})(django.jQuery);

// based on the project, milestone will be loaded

var $ = django.jQuery.noConflict();

function project_change()
{
    var project_id = $('#id_Project').val();
    $.ajax({
    "type"      : "GET",
  "url"         : "/product_change/?project_id="+project_id,
    "dataType"  : "json",
  "cache"       : false,
    "success"   : function(json) {
        $('#id_Milestone > option').remove();
        for(var j = 0; j < json.length; j++){
            $('#id_Milestone').append($('<option></option>').val(json[j][0]).html(json[j][1]));
        }
    }           
})(jQuery);
}

Include the following in views.py:

from django.shortcuts import HttpResponse
from django.utils import simplejson

from ticket.models import Milestone

def project_choices(request): 
    milestone_list = []
    project_id = request.GET.get('project_id')
    milestones = Milestone.objects.filter(project = project_id)    
    [milestone_list.append((each_milestone.pk,each_milestone.name)) for each_milestone in milestones]
    json = simplejson.dumps(milestone_list)
    return HttpResponse(json, mimetype='application/javascript')

In urls.py:

from ticket.views import project_choices

urlpatterns = patterns(
    (r'^product_change/', project_choices),
)

In admin.py where you want to load milestone based on project:

class Media:
    js = ['/path/to/project_change.js',]

I hope this will help you.