在基于Django类的视图中避免重复

Question

I am writing a web application in Django, which is used in a particular way. Instead of using models stored in a database, it builds forms dynamically from JSON data gathered from another application and platform using REST API.

The web page renders a form, which displays a list of mathematical parameters and their values. The user can then change (or not) those values and press a "Run" button to display some calculation results.

The forms are built from data obtained by querying JSON data via a URL (which gives me the list of parameters and their initial values). By specification, I have to use Django and do not use the database to store any parameter value data (the only data which are stored are the URL addresses of the JSON data).

I ended up with some working solution, using CBV. I have a DetailedView, of that structure:

class SimulationView(DetailView):
    template_name='template.html'
    model=SimModel # provides URLs for REST API (URLs for querying parameter list and simulation function)

    # this is used to display the page with GET
    def get_context_data(self, **kwargs):
        # conn.request function that returns param_JSON in JSON/REST
        # for a SUBSET of parameters in param_JSON build a list of entries named init_entries. Note not all parameters from the JSON request are used for the user interface.
        # form = paramForm(initial=init_entries) and store in context['form']
        return context

    def post(self, request, *args, **kwargs):
        # because the user may have changed parameter values, need to rebuild the JSON dataset to return to the URL with a simulation request
        # conn.request function that returns param_list in JSON/REST
        # for each param in JSON param_list build a list of entries
        # form = paramForm(request.POST, request.FILES, initial=init_entries) and store in context['form']
        # use form data to build REST request for the simulation function
        # conn.request simulation function and get result in JSON
        # store result in context['result']
        return render(request, 'template.html', context)

template.html is reponsible to display both the initial form when doing a GET, and the results as well when doing a POST.

As you can see, there is a performance issue. When you do GET to build the page, you have to do the REST connection to get the data and build the form and interface (this is normal). But when you POST to request simulation, you need to run the URL connection again to get the parameter list in JSON format, change the values, and then request simulation results. Please note that the REST request returns many more parameters than the one displayed to the user, hence it is not possible to use only the form data to build a proper JSON request. This works, but is inefficient. I tried to store param_JSON in a field of the class, but this does not work: the class is instanciated again when doing a POST, and param_JSON values are lost.

Do I need a get function? Or am I doing it totally wrong? In general, is there a better way? Thanks a lot in adavance for your suggestions.

Answer 1

Class based views are specifically designed to prevent you storing things in instance attributes, since this is not thread-safe; data would be shared between all requests.

The place to store data between separate requests is the session .

Answer 2

I am going back to my original question. I was wondering if the best solution was to use AJAX? I render the form once when user accesses the page via GET, and then POST calls are processed with AJAX, which only updates the result part of the page (graphs, table) without rendering the form again. Does that sound a reasonable solution?