CODEWITHSUNDEEP
pythondjangosortingmodelforeign-keys
user2905333
user2905333

Reputation: 35

Django order by foreign key

I was programming a function in python that required a group of objects of a model to be ordered by a specific parameter (the codename of a problem), this parameter resulted to be a string. When I sorted it inside the Problems table, it worked correctly, however, when I sorted it inside ProblemUser model (using order_by) the sort was completely incorrect respecting the real results.

I managed to work it around by sorting the elements AFTER i got it from the model using sorted() function, however, i am still with the doubt on how to sort a foreign key in the order_by function.

class Problem(models.Model):
    problem_name = models.CharField(max_length=256,default='Unnamed')
    source = models.CharField(max_length=200)
    url = models.CharField(max_length=200)
    codename = models.CharField(max_length=200, primary_key=True)
    difficulty = models.CharField(max_length=32,default='UNRATED')

class ProblemUser(models.Model):
    problem = models.ForeignKey(Problem)
    handler = models.ForeignKey(Handler)
    solved = models.BooleanField(default=True)
    voted = models.BooleanField(default=False)
    entry = models.DateField()


t = ProblemUser.objects.filter(solved=1, handler=Handler.objects.get(id=1)).order_by('problem')

t[0].problem.codename < t[42].problem.codename
False

t[1].problem.codename < t[42].problem.codename
True

I also tried order_by('problem__codename')

Some codenames examples are (these are outputs that i remember to have seen when i ordered by the foreign key):

S_1_T
S_1000_E
S_1001_F
.
.
.
S_2_P

Thank you for your time and help! :).

Upvotes: 1

Views: 3755

Answers (1)

earlymorningtea
earlymorningtea

Reputation: 508

try it like that please.

t = ProblemUser.objects.filter(solved=1, handler=Handler.objects.get(id=1)).order_by('problem__codename')

Upvotes: 1

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