Django: implementing JOIN using Django ORM?

Consider using models.ForeignKey(Question) instead of question_id = IntegerField().

This is the optimal (more relational) way to express the relationship between Questions and Answers you are trying to portray.

This way you can simply call Answers.objects.filter(question_id=<id>) and get exactly what you're looking for.

    class Question(models.Model):
      title = models.CharField(max_length=70)
      details = models.TextField()

    class Answer(models.Model):
      question = models.ForeignKey('Question')
      details = models.TextField()

    id = <whatever_id>    
    answers = Question.objects.get(id=id).answer_set.all()

This is exactly what select_related() does. The only gotcha is that you have to start with the Answer model, rather than Question, but the result is the same:

answers = Answer.objects.filter(question_id=1).select_related() 

Now each answer object has a pre-fetched 'question' attribute, and accessing it won't hit the db again.