[FIXED] Deleting a ManytoMany Relationship Data in Django Project

Issue

I have tried to fix this issue for a while.

I have a model where there are logs entered by users and saved in Log Model. Also there is ActiveSession Model which has a ManytoMany relationship with Log Model.

In My views I am getting the POST and saving them in the Log Model. The next step is my issue where I am trying to add unqiue Logs inside the ActiveSession Model. By unique I mean by searching a field called 'log_order' in the Log Model.

The desired outcome is to:

1: Get the POST form and save the Log details in the Log Model

2: Search if the new saved Log has been previously added the many to many relation log under Active Session Model

3: If there is no Log in the ActiveSession Model to add the new Log in the Post to the activesession

4: If there are logs previously saved in ActiveSession to search for the log_order related to these logs

5: If there is no same log_order to add the new Log in the Post to the activesession

6: If the log_order is existing inside the activesession logs to delete this specific log and to add the new Log in the Post to the activesession

Models.py:

class Log(models.Model):
    ...................................
    log_order = models.IntegerField(validators=[MinValueValidator(1)],blank=True, null=True)
    date = models.DateTimeField(...........)

class LogForm(forms.Form):
    .............................
    log_order = forms.IntegerField()

class ActiveSession(models.Model):
    log = models.ManyToManyField(Log)
    ..................................

Views.py:

def addlog(request, id):
    active_session = ActiveSession.objects.get(id=ActiveSession.objects.last().id)
        if request.method == 'POST':
            form = LogForm(request.POST)
            if form.is_valid():
                data = Log()
                data.log_order = request.POST.get('log_order')
                data.log_repetitions = form.cleaned_data['log_repetitions']
                data.log_weight = form.cleaned_data['log_weight']
                data.save()
                if active_session.log.values():
                    for i in active_session.log.values():
                        existing = i['log_order']
                        new = data.log_order
                        if int(existing) == int(new):
                            active_session.delete(active_session.log)
                            active_session.log.add(data)
                            active_session.save()
                        else:
                            active_session.log.add(data)
                else:
                    active_session.log.add(data)   

I have tried to save the data and update() but nothing is changing the dictionary the same exisiting outcome is printed and the new data is not replacing the existing ones. My objective is replace and avoid duplicating.

Update: I am also thought of if the keys is i['log_order'] is equal to data.log_order to delete the whole dictionary and add the new data whichever is easier

Trial: With the below trial I got 'ManyRelatedManager' object is not subscriptable. I am not sure if I am going the wrong direction.

                if active_session.log.values():
                    for i in range(len(active_session.log.values())):
                        new = data.log_order
                        if active_session.log[i]['log_order'] == new:
                            active_session.save()
                        else:
                            active_session.log.add(data)
                else:
                    active_session.log.add(data)

Here is the current query:

<QuerySet [{'log_order': 1}, {'log_order': 1}]>

here is the requested query:

<QuerySet [{'log_order': 1}]>

Solution

I have tried and tested your code and found some issues with it. Below, there is the code snippet I tested and it works.

I am not completely sure what is the purpose for the code, but I think you might find the method update_or_create useful (also works on related managers such as your log). Here is a link to Django docs.

def addlog(request, id):
    if request.method == 'POST':
        # Moved this part to the POST section of the view. It is sufficient to simplify
        # the query in this way. Also, you probably want to check if there are sessions
        # in the DB. Otherwise, the code would break. This returns a 404 in case there
        # are absolutely no sessions.
        active_session = ActiveSession.objects.last()
        if active_session is None:
            return Http404()

        form = LogForm(request.POST)
        if form.is_valid():
            data = Log()
            # Use form.cleaned_data instead of log_order. Form validates the data, POST dict doesn't.
            data.log_order = form.cleaned_data['log_order']
            # Ignored because it's missing from the model code
            # data.log_repetitions = form.cleaned_data['log_repetitions']
            # data.log_weight = form.cleaned_data['log_weight']
            data.save()

            # Use Django ORM querysets instead of values()
            # See https://www.django-antipatterns.com/antipattern/over-use-of-values.html
            active_session_logs = active_session.log.filter(log_order=data.log_order)
            if active_session_logs.exists():
                # Suggestion: try to use update() instead of a combination of delete & add.
                # It reduces two SQL queries to one.
                active_session_logs.delete()
            active_session.log.add(data)
            # After using RelatedManager.add(), no need to call save(), the changes
            # are persisted in the DB simply by using add().

            # Always redirect after successfully processing the form.
            return redirect(reverse('test_73764999:add-log', args=(data.id,)))
        else:
            # If there are errors, re-render the same form with errors
            return render(request, 'test_73764999/form.html', {
                'form': form, 'id': id,
            })
    else:
        # If this is a GET request, render an empty form
        form = LogForm()

    return render(request, 'test_73764999/form.html', {
        'form': form, 'id': id,
    })

Answered By - vinkomlacic