django query use aggregate on joined table - django

Question

In my project , Each candidate can take part in some assessments, each assessment has some tests and each test has some questions in it and candidates should answer the questions.
at the end of the test , scores of the questions are saved in question_score field (in QuestionResult model) automatically and the score of test is saved in test_score (which is average of question scores)
In TestOfAssessment model each test has a weight and I want to add a field to candidate model as assessment_score and write a method in candidate class model which calculate the score of assessment based on weight of each test and score of it
How can I use aggregate in my query with these joins on tables?
the simplified models are :
Assessment:
class Assessment(BaseModel):
title = models.CharField(max_length=255)
tests = models.ManyToManyField(
'exam.Test',
related_name='assessments',
blank=True,
through='TestOfAssessment',
)
candidates = models.ManyToManyField(
'user.User',
related_name='taken_assessments',
blank=True,
through='candidate.Candidate'
)
def __str__(self):
return self.title
Test:
class Test(BaseModel):
class DifficultyLevel(models.IntegerChoices):
EASY = 1
MEDIUM = 2
HARD = 3
questions = models.ManyToManyField(
'question.Question',
related_name='tests',
blank=True,
help_text='Standard tests could have multiple questions.',
)
level = models.IntegerField(default=1, choices=DifficultyLevel.choices)
title = models.CharField(max_length=255)
summary = models.TextField()
def __str__(self):
return self.title
TestOfAssessment:
class TestOfAssessment(models.Model):
assessment = models.ForeignKey('Assessment', on_delete=models.CASCADE)
test = models.ForeignKey('exam.Test', on_delete=models.CASCADE)
weight = models.PositiveSmallIntegerField(default=1)
order = models.IntegerField(default=0)
class Meta:
unique_together = ('assessment', 'test')
def __str__(self) -> str:
return f"{self.assessment} - {self.test}"
Question :
class Question(BaseModel):
question_text = models.TextField()
def __str__(self):
return truncatewords(self.question_text, 7)
TestResult:
class TestResult(BaseModel):
candidate = models.ForeignKey(
'Candidate',
on_delete=models.CASCADE,
related_name='test_results',
)
test = models.ForeignKey(
'exam.Test',
on_delete=models.CASCADE,
)
test_score = models.DecimalField(default=0.00, max_digits=5, decimal_places=2)
def __str__(self):
return f'{self.candidate.user.email} - {self.test.title}'
Candidate :
class Candidate(BaseModel):
assessment = models.ForeignKey(
'assessment.Assessment',
on_delete=models.CASCADE,
)
user = models.ForeignKey(
'user.User',
on_delete=models.CASCADE,
)
is_rejected = models.BooleanField(default=False)
def __str__(self):
return f'{self.user.email} - {self.assessment.title}'
QuestionResult :
class QuestionResult(BaseModel):
test = models.ForeignKey(
'TestResult',
on_delete=models.CASCADE,
related_name='question_results',
)
question = models.ForeignKey(
'question.Question',
on_delete=models.CASCADE,
related_name='results',
)
result = models.TextField(
null=True,
blank=True,
)
answer_score = models.DecimalField(default=0.00, max_digits=5, decimal_places=2)
def __str__(self):
return f'{self.test.candidate.user.email} - {self.question}'