python - Django annotate() 错误 AttributeError : 'CharField' object has no attribute 'resolve_expression'

Question

你好，我想将更多字段连接到 Django 中，但即使是这个简单的代码:

    Project.objects.annotate(
        companyname=Concat('company__name',Value('ahoj')),output_field=CharField()    
    )

给我一​​个错误:

AttributeError: 'CharField' object has no attribute 'resolve_expression'

回溯:

  File "/root/MUP/djangoenv/lib/python3.4/site-packages/django/db/models/manager.py", line 122, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "/root/MUP/djangoenv/lib/python3.4/site-packages/django/db/models/query.py", line 908, in annotate
    clone.query.add_annotation(annotation, alias, is_summary=False)
  File "/root/MUP/djangoenv/lib/python3.4/site-packages/django/db/models/sql/query.py", line 986, in add_annotation
    annotation = annotation.resolve_expression(self, allow_joins=True, reuse=None,
AttributeError: 'CharField' object has no attribute 'resolve_expression'

Answer 1

你在错误的地方有一个右括号。 output_field 是 Concat 的参数，而不是 annotate 的参数。应该是:

Project.objects.annotate(
    companyname=Concat('company__name', Value('ahoj'), output_field=CharField()),    
)