Question

让Post成为模特。我需要编写一个具有＆＃34;常数＆＃34;字段type，其值为每个对象的字符串"X"。

我尝试执行以下操作：

>>> Post.objects.all().annotate(type="X")
Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/home/porton/.virtualenv/opus/lib/python3.6/site-packages/django/db/models/query.py", line 929, in annotate
    clone.query.add_annotation(annotation, alias, is_summary=False)
  File "/home/porton/.virtualenv/opus/lib/python3.6/site-packages/django/db/models/sql/query.py", line 982, in add_annotation
    annotation = annotation.resolve_expression(self, allow_joins=True, reuse=None,
AttributeError: 'str' object has no attribute 'resolve_expression'

为什么错误以及如何解决我的问题？

请注意，当我.union()多个查询在一起时，我需要这个来区分不同类型的结果：

    q1 = paybills.models.PaymentSuccess.objects.all().annotate(type='PaymentSuccess').values('created', 'type')
    q2 = paybills.models.SubscriptionSuccess.objects.all().annotate(type='SubscriptionSuccess').values('created', 'type')
    q3 = paybills.models.SubscriptionPayment.objects.all().annotate(type='SubscriptionPayment').values('created', 'type')
    q4 = paybills.models.UnsubscriptionSuccess.objects.all().annotate(type='UnsubscriptionSuccess').values('created', 'type')
    q = q1.union(q2, q3, q4, all=True).order_by('-created')

Answer 1

尝试使用Value：

from django.db.models import Value
Post.objects.all().annotate(type=Value("X"))

Answer 2

在这种情况下，您无需使用from django.db.models import Value q1 = paybills.models.PaymentSuccess.objects.annotate(type=Value('PaymentSuccess')).values('created', 'type')

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Django：annotate（）不起作用

2 个答案: