关于python：在save（）函数中访问Django ManyToMany

Django ManyToMany access in save() function

我想在我的模型的.save()方法期间基于用户输入创建其他对象。该信息存储在多个关系.available_specs中。

如果有人按两次save，我的代码就可以工作，但第一次不行。这个问题也在save()函数中的django foreign key access注释中描述。

我要做的是：

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def save(self, *args, **kwargs):

my_save_result = super().save(*args, **kwargs) #save first to create an id
self.refresh_from_db() #just as a test, did not help at all

#the following line is the problem:
# in the first save, available_specs.all() returns []
# when I re-open the model and save again, I get the correct list
for spec in self.available_specs.all():
VehicleSpec.objects.get_or_create(vehicle=self, spec=spec)

return my_save_result

我使用的是python 3.5和django 1.9

编辑：我尝试使用以下代码使用post_save()信号(并删除了overrided save()-方法)：

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@receiver(post_save, sender=VehicleModel)
def create_dependent_vehicle_specs(sender, **kwargs):
vehicle = kwargs['instance']

#in the first save-process I get an empty list here,
#after I hit save again, the code works.
print(vehicle, vehicle.available_specs.all())
for spec in vehicle.available_specs.all():
VehicleSpec.objects.get_or_create(vehicle=vehicle, spec=spec)

号

edit2:m2m_变戏法了：

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@receiver(m2m_changed, sender=VehicleModel)
def create_dependent_vehicle_specs(sender, **kwargs):
vehicle = kwargs['instance']
for spec in vehicle.available_specs.all():
VehicleSpec.objects.get_or_create(vehicle=vehicle, spec=spec)

m2m_changed.connect(create_dependent_vehicle_specs, sender=VehicleModel.available_specs.through) # @UndefinedVariable

btw：这里有一个相关的问题：django从post-save信号访问许多字段