How to find a bug in Django and Ajax interaction?

Question

JavaScript

Hello.

I'm trying to make an updated select of models depending on the selected brand, but somewhere there is an error, I can't find it. That is, I do not get the brand_slug value from the POST request, if I write for example brand_slug = 'mazda', then everything will work.

viesws

@ensure_csrf_cookie
def ajax_get_mark(request):
  brand_slug = request.POST.get('brand_slug', '')
  marks = Mark.objects.filter(is_active=True, brand__slug=brand_slug)
  t = get_template('ajax/filter-models.html')
  response = t.render(Context({'marks': marks,}))
  response = response.encode('utf-8')
  return HttpResponse(json.dumps(response), content_type='application/json; charset=UTF-8',)

js

$('#brand').change(function(e) {
      var brand_slug = $(this).find(':selected').val();
      e.preventDefault();
      $.ajax({ 
        url: '{% url "seller.views.ajax_get_mark" %}',
        type: 'POST', 
        data: {
            'brand_slug' :  brand_slug,
        },
        dataType: 'json', 
        contentType: "application/json; charset=utf-8",  
        success: function (response, brand_slug) {
          console.log(response, brand_slug);
            // $('#mark').html(response);
        },
        error: function(){
            alert("Ошибка запроса");
        },
      }); 
    	});

Answer 1

The reason for this is the string 'contentType: "application/json; charset=utf-8",'.
You send a djang post request with the body converted to json format. In request.POST, django puts only simple requests, that is, those that came in the format 'application/x-www-form-urlencoded'.
Remove this line and it should work.