它不会将更新的值保存到数据库表ajax

Question

=== html === 一个项目有很多费用，而我的下拉列表显示该项目的所有费用。它还将允许用户从下拉列表中选择其他值，然后单击“更新”按钮。它不会给出任何错误，但是不会将下拉列表中的选定值保存到数据库中。 任何帮助将不胜感激。

<select id="select_dropdown">
    {% if project.id and emp.id %}
        {% for expense in emp.expense_set.all %}
            {% if expense.city %}
                <option value="{{expense.id}}" selected="selected">{{expense.expense_type}}</option>
            {% else %}
                <option value="{{expense.id}}">{{expense.expense_type}}</option>
            {% endif %}
        {% endfor %}
    {% endif %}
</select> 

==== js =======

        $("#save_change").click(function(e) {
                e.preventDefault();
                console.log("update fucntion is working!");
                var value = $("#select_dropdown").find(":selected").val();
                var text = $("#select_dropdown option:selected").text();
                var project_id = $("#project_id").val();
                var emp_id = $("#emp_id").val();
                console.log(emp_id);
                $.ajax({
                        url: "{% url 'update_form' %}",
                        //url: "/ajax/update_form/",
                        method: "POST",
                        data: {
                                "value": value,
                                "text": text,
                                "project_id": project_id,
                                "emp_id": emp_id,
                                csrfmiddlewaretoken: '{{ csrf_token }}',
                        },
                        dataType: "json",
                        success: function(data){
                                console.log("success");
                                console.log(data);
                        },
                        error: function(error_data){
                                console.log("error")
                                console.log(error_data)
                        }

                });
                return false;

=== views.py ===

@csrf_exempt
def update_form(request):
        if request.method == "POST" and request.is_ajax():
                expense_id = request.POST.get('value')
                expense_type = request.POST.get('text')
                project_id = request.POST.get('project_id')
                emp_id = request.POST.get('emp_id')
                project_id = request.POST.get('project_id')

                for exp in expense:
                        exp.expense_type = expense_type
                        exp.save()

                data = serializers.serialize("json", expense)

        return HttpResponse(data, content_type="application/json")