如何将多个ManytoMany实例保存到Django对象?

问题描述 投票:0回答:1

我有一个带有多个Question对象的django应用。问题和测验通过ManyToManyField相关联。我想创建测验对象,以便每个测验被随机分配3个问题。

我已经尝试在模型中创建一个保存方法,在该模型中,我:使用查询集获取3个问题,保存测验实例(以保存ID),将查询集设置为测验,然后再次保存。我在该主题上进行的大多数搜索都显示出人们在哪里使用表单保存m2m对象。

甚至更好,是否可以使用视图向一个测验对象设置3个问题?最终,这是我想要去的地方。用户将在视图中使用request.GET选择LearnGoal,并且此LearnGoal将限制将添加到测验中的问题。

到目前为止,我的models.py:

class LearnGoal(models.Model):
    goal_name = models.CharField(max_length=12)
    goal_description = models.TextField()

class Question(models.Model):
    name = models.CharField(max_length=12)
    learngoal = models.ForeignKey(LearnGoal, on_delete=models.CASCADE)
    q_text = models.TextField()
    answer = models.CharField(max_length=12)

class Quiz(models.Model):
    """quiz which will have three questions."""
    name = models.CharField(max_length=12)
    questions = models.ManyToManyField(Question)
    completed = models.DateTimeField(auto_now_add=True)
    my_answer = models.CharField(max_length=12)

    def save(self, *args, **kwargs):
        """need to create an instance first, for the m2m"""
        super(Quiz, self).save(*args, **kwargs)
        """get 3 random questions"""
        three_questions = Quiz.objects.all().order_by('?')[0:3]
        self.questions.set(three_questions)
        super(Quiz, self).save(*args, **kwargs)

我已经尝试了上述代码的一些变体。当前,此代码给出错误:'Question' instance expected, got <Quiz: Quiz object (4)>行中的self.questions.set(five_questions)

如何将多个问题保存到一个测验实例中?

django manytomanyfield
1个回答
1
投票

Quiz.save方法中,您可以执行以下操作:

class Quiz(models.Model):
    ...
    ...

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.add_questions = False

    def save(self, *args, **kwargs):
        # We need this to prevent updating questions
        # on updating the Quiz instance
        if self.pk is None:
            self.add_questions = True
        super().save(*args, **kwargs)

        if self.add_questions:
            # No need to run save again; M2M relationships are set
            # through an intermediate model
            self.questions.set(Question.objects.order_by('?')[:3])

请注意,随机排序(order_by('?'))速度很慢,但这是否会完全影响您取决于使用情况。

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