为什么获取复杂聚合需要别名错误？
why getting Complex aggregates require an alias error?
我在 Django 上工作，我有两个模型 Gigs 和 Orders 我正在计算每个演出订单的平均完成时间.
在 order 模型中我有两个字段 order start time （只要卖家接受订单我就会发送）和 订单完成时间（我在卖家发货时发送）订单。
但问题是，如果我在订单 table 中有与某个演出相关的数据，并且我检索了该演出，那么它工作得很好，但如果我尝试检索还没有订单的演出（在订单 table 没有 record/field 包含 item/gig) 然后它给了我以下错误
Complex aggregates require an alias
Models.py
class Gigs(models.Model):
title = models.CharField(max_length=255)
category = models.ForeignKey(Categories , on_delete=models.CASCADE)
images = models.ImageField(blank=True, null = True, upload_to= upload_path)
price = models.DecimalField(max_digits=6, decimal_places=2)
details = models.TextField()
seller = models.ForeignKey(User,default=None, on_delete=models.CASCADE)
@property
def average_completionTime(self):
if getattr(self, '_average_completionTime', None):
return self._average_completionTime
return self.gig.aggregate(Avg(F('orderCompletedTime') - F('orderStartTime')))
class Orders(models.Model):
buyer = models.ForeignKey(User,default=None, on_delete=models.CASCADE,related_name='buyer_id')
seller = models.ForeignKey(User,default=None, on_delete=models.CASCADE,related_name='seller_id')
item = models.ForeignKey(Gigs,default=None, on_delete=models.CASCADE,related_name='gig')
payment_method= models.CharField(max_length=10)
address = models.CharField(max_length=255)
mobile = models.CharField(max_length=13,default=None)
quantity = models.SmallIntegerField(default=1)
status = models.CharField(max_length=13,default='new order')
orderStartTime = models.DateTimeField(default=timezone.now)
orderCompletedTime = models.DateTimeField(default=timezone.now)
isCompleted = models.BooleanField(default=False)
created_at = models.DateTimeField(auto_now_add=True)
Views.py
class RetrieveGigsAPI(GenericAPIView, RetrieveModelMixin):
def get_queryset(self):
return Gigs.objects.annotate(
_average_completionTime=Avg(
ExpressionWrapper(F('gig__orderCompletedTime') - F('gig__orderStartTime'), output_field=DurationField()),
filter=Q(gig__isCompleted=True),
)
)
serializer_class = GigsSerializerWithAvgTime
permission_classes = (AllowAny,)
def get(self, request , *args, **kwargs):
return self.retrieve(request, *args, **kwargs)
Serializers.py
class GigsSerializerWithAvgTime(serializers.ModelSerializer):
average_completionTime = serializers.SerializerMethodField()
def get_average_completionTime(self, obj):
return obj.average_completionTime
class Meta:
model = Gigs
fields = ['id','title','category','price','details','seller','images','average_completionTime']
例子
例如，如果我们在订单 table 中有以下数据，其中项目是演出中的外键 table
现在，如果我检索演出 22，它运行良好，并为我提供 Api 中的所有字段，包括平均完成时间，但如果我想获得演出 23 或任何其他，它会给我错误
但我希望它应该 return 所有其他字段相同且平均完成时间：null
错误的完整引用
Environment:
Request Method: GET
Request URL: http://localhost:8000/seller/GigApi/23/
Django Version: 3.0.11
Python Version: 3.9.1
Installed Applications:
['django.contrib.admin',
'django.contrib.auth',
'django.contrib.contenttypes',
'django.contrib.sessions',
'django.contrib.messages',
'django.contrib.staticfiles',
'rest_framework',
'djoser',
'accounts',
'adminuser',
'seller',
'buyer',
'corsheaders']
Installed Middleware:
['django.middleware.security.SecurityMiddleware',
'django.contrib.sessions.middleware.SessionMiddleware',
'django.middleware.common.CommonMiddleware',
'django.middleware.csrf.CsrfViewMiddleware',
'django.contrib.auth.middleware.AuthenticationMiddleware',
'django.contrib.messages.middleware.MessageMiddleware',
'django.middleware.clickjacking.XFrameOptionsMiddleware',
'corsheaders.middleware.CorsMiddleware',
'django.middleware.common.CommonMiddleware']
Traceback (most recent call last):
File "C:\Python39\lib\site-packages\django\db\models\query.py", line 374, in aggregate
arg.default_alias
File "C:\Python39\lib\site-packages\django\db\models\aggregates.py", line 65, in default_alias
raise TypeError("Complex expressions require an alias")
During handling of the above exception (Complex expressions require an alias), another exception occurred:
File "C:\Python39\lib\site-packages\django\core\handlers\exception.py", line 34, in inner
response = get_response(request)
File "C:\Python39\lib\site-packages\django\core\handlers\base.py", line 115, in _get_response
response = self.process_exception_by_middleware(e, request)
File "C:\Python39\lib\site-packages\django\core\handlers\base.py", line 113, in _get_response
response = wrapped_callback(request, *callback_args, **callback_kwargs)
File "C:\Python39\lib\site-packages\django\views\decorators\csrf.py", line 54, in wrapped_view
return view_func(*args, **kwargs)
File "C:\Python39\lib\site-packages\django\views\generic\base.py", line 71, in view
return self.dispatch(request, *args, **kwargs)
File "C:\Python39\lib\site-packages\rest_framework\views.py", line 509, in dispatch
response = self.handle_exception(exc)
File "C:\Python39\lib\site-packages\rest_framework\views.py", line 469, in handle_exception
self.raise_uncaught_exception(exc)
File "C:\Python39\lib\site-packages\rest_framework\views.py", line 480, in raise_uncaught_exception
raise exc
File "C:\Python39\lib\site-packages\rest_framework\views.py", line 506, in dispatch
response = handler(request, *args, **kwargs)
File "C:\FYP\backend\seller\views.py", line 76, in get
return self.retrieve(request, *args, **kwargs)
File "C:\Python39\lib\site-packages\rest_framework\mixins.py", line 56, in retrieve
return Response(serializer.data)
File "C:\Python39\lib\site-packages\rest_framework\serializers.py", line 548, in data
ret = super().data
File "C:\Python39\lib\site-packages\rest_framework\serializers.py", line 246, in data
self._data = self.to_representation(self.instance)
File "C:\Python39\lib\site-packages\rest_framework\serializers.py", line 515, in to_representation
ret[field.field_name] = field.to_representation(attribute)
File "C:\Python39\lib\site-packages\rest_framework\fields.py", line 1870, in to_representation
return method(value)
File "C:\FYP\backend\seller\serializers.py", line 21, in get_average_completionTime
return obj.average_completionTime
File "C:\FYP\backend\seller\models.py", line 29, in average_completionTime
return self.gig.aggregate(Avg(F('orderCompletedTime') - F('orderStartTime')))
File "C:\Python39\lib\site-packages\django\db\models\manager.py", line 82, in manager_method
return getattr(self.get_queryset(), name)(*args, **kwargs)
File "C:\Python39\lib\site-packages\django\db\models\query.py", line 376, in aggregate
raise TypeError("Complex aggregates require an alias")
Exception Type: TypeError at /seller/GigApi/23/
Exception Value: Complex aggregates require an alias
正如@Iain Shelvington 所提到的，您可以像这样为聚合设置一个名称来解决错误：
return self.gig.aggregate(average_completion=Avg(F('orderCompletedTime') - F('orderStartTime')))['average_completion']
# ^^^ Add this
此外，由于在 get_queryset 中它可能已经有一个计算值，您可以尝试将 getattr 更改为 hasattr 并且只是 return：
@property
def average_completionTime(self):
if hasattr(self, '_average_completionTime'):
return self._average_completionTime
return self.gig.aggregate(
average_completion=Avg(F('orderCompletedTime') - F('orderStartTime'))
)['average_completion']
这是为了检查 _average_completionTime 是否已经为 gig 实例计算，以防止再次计算它。
我在 Django 上工作，我有两个模型 Gigs 和 Orders 我正在计算每个演出订单的平均完成时间.
在 order 模型中我有两个字段 order start time （只要卖家接受订单我就会发送）和 订单完成时间（我在卖家发货时发送）订单。
但问题是，如果我在订单 table 中有与某个演出相关的数据，并且我检索了该演出，那么它工作得很好，但如果我尝试检索还没有订单的演出（在订单 table 没有 record/field 包含 item/gig) 然后它给了我以下错误
Complex aggregates require an alias
Models.py
class Gigs(models.Model):
title = models.CharField(max_length=255)
category = models.ForeignKey(Categories , on_delete=models.CASCADE)
images = models.ImageField(blank=True, null = True, upload_to= upload_path)
price = models.DecimalField(max_digits=6, decimal_places=2)
details = models.TextField()
seller = models.ForeignKey(User,default=None, on_delete=models.CASCADE)
@property
def average_completionTime(self):
if getattr(self, '_average_completionTime', None):
return self._average_completionTime
return self.gig.aggregate(Avg(F('orderCompletedTime') - F('orderStartTime')))
class Orders(models.Model):
buyer = models.ForeignKey(User,default=None, on_delete=models.CASCADE,related_name='buyer_id')
seller = models.ForeignKey(User,default=None, on_delete=models.CASCADE,related_name='seller_id')
item = models.ForeignKey(Gigs,default=None, on_delete=models.CASCADE,related_name='gig')
payment_method= models.CharField(max_length=10)
address = models.CharField(max_length=255)
mobile = models.CharField(max_length=13,default=None)
quantity = models.SmallIntegerField(default=1)
status = models.CharField(max_length=13,default='new order')
orderStartTime = models.DateTimeField(default=timezone.now)
orderCompletedTime = models.DateTimeField(default=timezone.now)
isCompleted = models.BooleanField(default=False)
created_at = models.DateTimeField(auto_now_add=True)
Views.py
class RetrieveGigsAPI(GenericAPIView, RetrieveModelMixin):
def get_queryset(self):
return Gigs.objects.annotate(
_average_completionTime=Avg(
ExpressionWrapper(F('gig__orderCompletedTime') - F('gig__orderStartTime'), output_field=DurationField()),
filter=Q(gig__isCompleted=True),
)
)
serializer_class = GigsSerializerWithAvgTime
permission_classes = (AllowAny,)
def get(self, request , *args, **kwargs):
return self.retrieve(request, *args, **kwargs)
Serializers.py
class GigsSerializerWithAvgTime(serializers.ModelSerializer):
average_completionTime = serializers.SerializerMethodField()
def get_average_completionTime(self, obj):
return obj.average_completionTime
class Meta:
model = Gigs
fields = ['id','title','category','price','details','seller','images','average_completionTime']
例子
例如，如果我们在订单 table 中有以下数据，其中项目是演出中的外键 table
但我希望它应该 return 所有其他字段相同且平均完成时间：null
错误的完整引用
Environment:
Request Method: GET
Request URL: http://localhost:8000/seller/GigApi/23/
Django Version: 3.0.11
Python Version: 3.9.1
Installed Applications:
['django.contrib.admin',
'django.contrib.auth',
'django.contrib.contenttypes',
'django.contrib.sessions',
'django.contrib.messages',
'django.contrib.staticfiles',
'rest_framework',
'djoser',
'accounts',
'adminuser',
'seller',
'buyer',
'corsheaders']
Installed Middleware:
['django.middleware.security.SecurityMiddleware',
'django.contrib.sessions.middleware.SessionMiddleware',
'django.middleware.common.CommonMiddleware',
'django.middleware.csrf.CsrfViewMiddleware',
'django.contrib.auth.middleware.AuthenticationMiddleware',
'django.contrib.messages.middleware.MessageMiddleware',
'django.middleware.clickjacking.XFrameOptionsMiddleware',
'corsheaders.middleware.CorsMiddleware',
'django.middleware.common.CommonMiddleware']
Traceback (most recent call last):
File "C:\Python39\lib\site-packages\django\db\models\query.py", line 374, in aggregate
arg.default_alias
File "C:\Python39\lib\site-packages\django\db\models\aggregates.py", line 65, in default_alias
raise TypeError("Complex expressions require an alias")
During handling of the above exception (Complex expressions require an alias), another exception occurred:
File "C:\Python39\lib\site-packages\django\core\handlers\exception.py", line 34, in inner
response = get_response(request)
File "C:\Python39\lib\site-packages\django\core\handlers\base.py", line 115, in _get_response
response = self.process_exception_by_middleware(e, request)
File "C:\Python39\lib\site-packages\django\core\handlers\base.py", line 113, in _get_response
response = wrapped_callback(request, *callback_args, **callback_kwargs)
File "C:\Python39\lib\site-packages\django\views\decorators\csrf.py", line 54, in wrapped_view
return view_func(*args, **kwargs)
File "C:\Python39\lib\site-packages\django\views\generic\base.py", line 71, in view
return self.dispatch(request, *args, **kwargs)
File "C:\Python39\lib\site-packages\rest_framework\views.py", line 509, in dispatch
response = self.handle_exception(exc)
File "C:\Python39\lib\site-packages\rest_framework\views.py", line 469, in handle_exception
self.raise_uncaught_exception(exc)
File "C:\Python39\lib\site-packages\rest_framework\views.py", line 480, in raise_uncaught_exception
raise exc
File "C:\Python39\lib\site-packages\rest_framework\views.py", line 506, in dispatch
response = handler(request, *args, **kwargs)
File "C:\FYP\backend\seller\views.py", line 76, in get
return self.retrieve(request, *args, **kwargs)
File "C:\Python39\lib\site-packages\rest_framework\mixins.py", line 56, in retrieve
return Response(serializer.data)
File "C:\Python39\lib\site-packages\rest_framework\serializers.py", line 548, in data
ret = super().data
File "C:\Python39\lib\site-packages\rest_framework\serializers.py", line 246, in data
self._data = self.to_representation(self.instance)
File "C:\Python39\lib\site-packages\rest_framework\serializers.py", line 515, in to_representation
ret[field.field_name] = field.to_representation(attribute)
File "C:\Python39\lib\site-packages\rest_framework\fields.py", line 1870, in to_representation
return method(value)
File "C:\FYP\backend\seller\serializers.py", line 21, in get_average_completionTime
return obj.average_completionTime
File "C:\FYP\backend\seller\models.py", line 29, in average_completionTime
return self.gig.aggregate(Avg(F('orderCompletedTime') - F('orderStartTime')))
File "C:\Python39\lib\site-packages\django\db\models\manager.py", line 82, in manager_method
return getattr(self.get_queryset(), name)(*args, **kwargs)
File "C:\Python39\lib\site-packages\django\db\models\query.py", line 376, in aggregate
raise TypeError("Complex aggregates require an alias")
Exception Type: TypeError at /seller/GigApi/23/
Exception Value: Complex aggregates require an alias
正如@Iain Shelvington 所提到的，您可以像这样为聚合设置一个名称来解决错误：
return self.gig.aggregate(average_completion=Avg(F('orderCompletedTime') - F('orderStartTime')))['average_completion']
# ^^^ Add this
此外，由于在 get_queryset 中它可能已经有一个计算值，您可以尝试将 getattr 更改为 hasattr 并且只是 return：
@property
def average_completionTime(self):
if hasattr(self, '_average_completionTime'):
return self._average_completionTime
return self.gig.aggregate(
average_completion=Avg(F('orderCompletedTime') - F('orderStartTime'))
)['average_completion']
这是为了检查 _average_completionTime 是否已经为 gig 实例计算，以防止再次计算它。