有 2 个简单模型:
class Question(TimeStampedModel):
text = models.CharField(max_length=40)
class Answer(TimeStampedModel):
question = models.ForeignKey(Question, related_name='answers')
is_agreed = models.BooleanField()
author = models.ForeingKey(User, related_name='answers')
还有我的问题:
In [18]: Question.objects.count()
Out[18]: 3
我需要用“is_user_agreed”和“answers_amount”字段注释查询集:
In [18]: user = User.objects.first()
In [19]: qs = Question.objects.annotate(
...: is_user_agreed=Case(
...: When(answers__in=user.answers.filter(is_agreed=True), then=Value(True)),
...: When(answers__in=user.answers.filter(is_agreed=False), then=Value(False)),
...: default=Value(None),
...: output_field=NullBooleanField(),
...: ),
...: ).annotate(answers_amount=Count('answers'))
...: qs.count()
Out[19]: 4
^ 这里计数是 4,但我在 db 中只有 3 个问题 :(
所以,我试过 distinct()
In [20]: qs.distinct().count()
Out[20]: 4 # but distinct doesn't work
In [21]: qs.distinct('id').count()
在最后一行代码之后我得到了这个异常:
NotImplementedError: annotate() + distinct(fields) is not implemented.
我也尝试过使用这个技巧 annotate(Count('id')).filter(id__count__gt=1)
但在这种情况下,我将丢失所有重复的行,而 qs.count() 是 2。
更新:问题是查询集中的重复行。
解决方案:(Vladimir 第二种方法的扩展变体)
user = User.objects.first()
user_agreed_questions = user.answers.filter(
is_agreed=True).values_list('question_id', flat=True)
user_not_agreed_questions = user.answers.filter(
is_agreed=False).values_list('question_id', flat=True)
Question.objects.annotate(
answer_amount=Count('answers'),
is_user_agreed=Case(
When(id__in=user_agreed_questions, then=True),
When(id__in=user_not_agreed_questions, then=False),
default=None,
output_field=NullBooleanField(),
),
)
最佳答案
试试这个:
Question.objects.annotate(
answer_amount=Count('answers'),
is_user_agreed=F('answers__is_agreed'),
).order_by('id', '-answers__is_agreed').distinct('id')
如果question
没有answers
,则question.is_user_agreed
为None
。如果 question
至少有一个 answer
为 answer.is_agreed=True
,则 question.is_agreed
为 真
。否则,is_user_agreed
为 False
。
或者这个:
agreed_questons = Answer.objects.filter(
is_agreed=True,
).values_list('question_id', flat=True).distinct()
Question.objects.annotate(
answer_amount=Count('answers'),
is_agreed=Case(
When(id__in=agreed_questions, then=True),
When(answers__isnull=True, then=None),
default=False,
output_field=NullBooleanField(),
),
)
agreed_questons
是 questions
的 id
列表,至少有一个 answer
with answer .is_agreed=True
.
关于python - Django: NotImplementedError: annotate() + distinct(fields) 未实现,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/38583295/