[Answer]-Django AttributeError in vews.py 'NoneType' object has no attribute 'all'

atrocity.location is a ForeignKey, so it points to a single City. With your current model, you should just use
city = atrocity.location to retrieve the single city associated with an Atrocity. You use .all() on a manager object representing a bunch of objects, such as City.objects, but your location field is just a single object.

If you want the Atrocity.location field to represent many cities, then you can use

location = models.ManyToManyField(City)

and call atrocity.location.all() to get all the location cities for atrocity.

Edit: It seems from your code that you might be trying to get a list of all cities which are the location for some Atrocity? If that’s the case, you could use

cities = list(set(map(lambda a: a.location, Atrocity.objects.all()))

and pass cities into your template. This gets the the location of each Atrocity object, and combines them into a set to remove duplicates.

Location is a foreign key. A foreign key references only one model. Then your code has no sense because .all() method is for query sets. Should be just:

cities = atrocity.location

What you are doing is wrong. There is a foreign key relationship so, each atrocity is related to only one location. So, you can not use all

Example:

#Each Atrocity is related to only one location
city = atrocity.location

#Each can be related to more than one atrocity
atrocities = location.atrocity_set.all()

And instead of looping through each Atrocity object to collect the city. It would be more efficient to do it on the database level. You can do a join query between City and Atrocity via this.

cities = City.objects.filter(id__in = Atrocity.objects.values_list('location', flat=True))