Best way to get ForeignKey Related Objects?

[Tobias Dacoir]

I have two Models as shown below. Now when I have a specific AudioQuestionPair and I do something like

print pair.answers

it works just fine. However I can not do:

for answer in pair.answers

Using pair.answers.get.all() does also not work. So I have to do

answers = Answer.objects.filter(audioQuestionPair=pair)

Isn't there a better way to design this? I can imagine that using objects.filter is more taxing on the database and uses more time than maybe another method?

class AudioQuestionPair(models.Model):
    audioData = models.ForeignKey(AudioData)
    question = models.ForeignKey(Question)
    database = models.ForeignKey(Database)
    votes = models.PositiveIntegerField(default=0)

    class Meta:
        verbose_name = "AudioData-Question Pair"
        verbose_name_plural = "AudioData-Question Pairs"

    def answers(self):
        return Answer.objects.filter(audioQuestionPair=self.pk)

    def __str__(self):
        return "Database %s: AudioData %s - Question %s with %s Votes and Answers: %s" % (self.database, self.audioData, self.question, self.votes, self.answers())

"""
 Answer for a specific Audio-Question Pair
 cumulative
"""
class Answer(models.Model):
    body = models.CharField(max_length=255)
    count = models.PositiveIntegerField(default=0)
    isGroundtruth = models.BooleanField(default=False)
    audioQuestionPair = models.ForeignKey(AudioQuestionPair)

    class Meta:
        verbose_name = "Answer to AudioQuestionPair"
        verbose_name_plural = "Answers to AudioQuestionPairs"

    def __str__(self):
        return "%s - %s times" % (self.body, self.count)

[Vijay Khemlani]

"answers" seems to be a method on the AudioQuestionPair class, so your call should be:

for answer in pair.answers():

    print answer

and "pair.answers.get.all()" does not make sense sinse "answers" is a method.

If you don't want to use a specific method, you can do this:

answers = pair.answer_set.all()

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[Tobias Dacoir]

Damn, you are right. pair.answers() works. I'm wondering why I didn't get a syntax error when calling it without the parenthesis (), because print still worked.

[Vijay Khemlani]

Python has higher order functions, so you can do things like this

m = pair.answers           # m refers to the method itself

print m        # Prints "method AudioQuestionPair.anwers of ..."

answers = m()              # Actually executes the method

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