Update dropdownlist with a new object created in a modal form

Hi there,

In one of my forms, there´s a dropdownlist to select the category of the object to be created. I also have a button to open a modal form with AJAX and create a new category. When the modal form is submitted, the whole page is redirected to the View of the new created object. Instead of that behaviour, I wanted the modal form to just close itself and return back the object to be added as option in the dropdownlist of the main form.

I tried several solutions found, none of them worked though.

Any ideas?

Thanks in advance!