Add "duplicate" objects to a table in Django - django

Question

I have a model called Song and another called Chord. They have a ManyToMany relationship through a label called ChordIndex.
A song might need to have the same chord more than once, which django would not allow. Hence, I gave the model an extra field (manually coded auto-incremental field) called index, so objects are not identical.
Still I can't add "duplicate" chords.
Nevertheless the approach works with a form and a POST method. But, if I use the POST method I am unable to set song field to default="lastSongByUser" because you can only query "user" inside a view.
models.py
class ChordIndex(models.Model):
def incrementalNumber():
objectCount = ChordIndex.objects.count()
if objectCount == None:
return 2
else:
return objectCount + 1
index = models.PositiveIntegerField(default=incrementalNumber)
chord = models.ForeignKey('Chord', on_delete=models.CASCADE)
song = models.ForeignKey('Song', on_delete=models.CASCADE)
views.py
def addchord_view(request, idChord):
user = request.user.profile
chord = Chord.objects.get(pk=idChord)
songsByUser = Song.objects.filter(uploader=user)
lastSongByUser = songsByUser.last()
previousPage = request.META.get('HTTP_REFERER')
filterUserLastSong = ChordIndex.objects.filter(song=lastSongByUser)
lastSongByUser.chords.add(chord)
thisObjectAdded = filterUserLastSong.last()
thisObjectAdded.save()
return HttpResponseRedirect(previousPage)
editchords.html
{% for chord in allChords %}
{% if chord.acronym != silent%}
<button class="btn btn-dark">{{ chord.acronym }}</button>
{% else %}
<button class="btn btn-primary"><a class="text-dark" href="{% url 'add-chord-view' idChord=chord.pk %}">next part</a></button>
{% endif %}
{% endfor %}
I would expect to get same results that from POST method.

Answer 1

You can add duplicate objects like this:
def addchord_view(request, idChord):
user = request.user.profile
chord Chord.objects.get(pk=idChord)
songsByUser = Song.objects.filter(uploader=user)
lastSongByUser = songsByUser.last()
previousPage = request.META.get('HTTP_REFERER')
filterUserLastSong = ChordIndex.objects.create(song=lastSongByUser, chord=chord)
return HttpResponseRedirect(previousPage)
Explanation
When you call ChordIndex.objects.create(song=lastSongByUser, chord=chord), it will create a new ChordIndex instance. Then if you call song.chords.all(), then you should get multiple chords for a song ordered by creation. You don't need to use index = models.PositiveIntegerField(default=incrementalNumber) field as well in your model, so you can remove that.