Understanding Full Join in Django - sql

Question

I have two models in my app:
# Create your models here.
class Melody(models.Model):
notes = models.JSONField()
bpm = models.IntegerField()
aimodel = models.CharField(max_length=200)
score = models.IntegerField(default=0)
person = models.ManyToManyField(settings.AUTH_USER_MODEL, related_name="melodies")
date_created = models.DateTimeField(default=timezone.now)
def __str__(self):
return str(self.id)
class Vote(models.Model):
user_score = models.IntegerField(validators=[MaxValueValidator(1), MinValueValidator(-1)])
melody = models.ForeignKey(Melody, on_delete=models.CASCADE, related_name="scores")
person = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE, related_name="voters")
def __str__(self):
return f"{self.person} - {self.melody} - {self.score}"
And I get the melodies of the current user by
# Get melodies of current user
melodies = Melody.objects.all().filter(person=person).order_by('-score')[start:end+1].values()
I would like to add to this results the vote of the user to each melody, if there is one, otherwise just null so I can loop over the melodies and retrieve the values:
melody.notes = ...
melody.bpm = ...
melody.user_score = This is the values I do not know still how to get, Null if user has not voted
I was reading about select_related but when I use it it always says
"Invalid field name(s) given in select_related: 'xxxx'. Choices are: (none)"
What am I missing?
EDIT
I solved it based on the answer of #Fnechz by making two queries and then looping over the elements so I can add the user_score to the melody:
# Get melodies of current user
melodies = Melody.objects.all().filter(person=person).order_by('-score')[start:end+1].values()
# Get votes of the user
votes = Vote.objects.all().filter(person=person)
for i, m_melody in enumerate(melodies):
for m_vote in votes:
if (m_vote.melody.id == m_melody['id']):
melodies[i]['user_score'] = m_vote.user_score
return JsonResponse({"melodies": list(melodies)})
Not sure if this is the best way to achieved it

Answer 1

I do not know if there is a direct method to accomplish what you want with a single query. But I guess concatenating the queryset results might work.
from itertools import chain
melodies = Melody.objects.all().filter(person=person).order_by('-score')[start:end+1].values()
votes = #query your vote model here to get the user_score
result_list = list(chain(melodies,votes))
If I have understood your question that might work