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我正在尝试按地理区域（Hexgrid_10km2）聚合模型（回复）。类似于 SQL 的“分组依据”。我正在使用 .values(Hexgrid_10km) 来执行此操作。然后我在上面注释一些数字。我在对 geojson 的序列化中收到以下错误：

“dict”对象没有属性“hexgrid_10km2”

但是回复确实有一个名为“hexgrid_10km2”的字段。

我想不通。我尝试过其他方法在 stackoverflow 上进行序列化，但似乎总是出错。有人知道我做错了吗？非常感谢！！

我正在使用 djangorestframework-gis

楷模

class Hexgrid_10km2(models.Model):
    lng = models.FloatField()
    lat = models.FloatField()
    polygon = models.MultiPolygonField(srid=4326)
    centroid = models.PointField(default=Point(0,0), srid=4326)

    def __str__(self):
        return f'lng: { self.lng } lat: {self.lat }'


class Animal (models.Model):
    name = models.CharField(max_length=200)


class Reply(models.Model):
    user = models.ForeignKey(User, on_delete=models.CASCADE)
    reply_date = models.DateTimeField()
    animal = models.ForeignKey(Animal, on_delete=models.CASCADE)
    ability = models.IntegerField(default = 0)
    hexgrid_10km2 = models.ForeignKey(Hexgrid_10km2, on_delete=models.CASCADE, null=True, blank=True)

    @property
    def polygon_10km2(self):
        return self.hexgrid_10km2.polygon

意见

from rest_framework.views import APIView
from rest_framework.response import Response
from.models import Animal, Reply, Hexgrid_10km2
from django.db.models import Avg, Sum

class ReplyHeatmapAPIView(APIView):
    def get(self, request, pk):
        animal = get_object_or_404(Animal, pk=pk)
        relevant = Reply.objects.filter(animal=animal)
        most_recent = relevant.filter(
            reply_date=Subquery(
                (Reply.objects
                    .filter(user=OuterRef('user'))
                    .values('user')
                    .annotate(most_recent=Max('reply_date'))
                    .values('reply_date')[:1]
                )
            )
        final = most_recent.values('hexgrid_10km2')
            .annotate(average_ability=Avg('ability'), sum_ability=Sum('ability'))
        serializer = ReplyHeatmapSerializer(final, many=True)
        return Response(serializer.data)

串行器

from rest_framework_gis.fields import GeometrySerializerMethodField
from rest_framework_gis.serializers import GeoFeatureModelSerializer

class ReplyHeatmapSerializer(GeoFeatureModelSerializer):
    """ A class to serialize hex polygons as GeoJSON compatible data """

    average_ability = serializers.FloatField()
    sum_ability = serializers.FloatField()

    polygon = GeometrySerializerMethodField()
    def get_polygon(self, obj):
        return obj.hexgrid_10km2.polygon

    class Meta:
        model = Reply
        geo_field = 'polygon'
        depth = 1
        id_field = False
        fields = ('id', 'average_abilty', 'sum_ability')

追溯

Traceback (most recent call last):
  File "C:\Users\anton\OneDrive\Documents\django\karate-project-2.2\venv\lib\site-packages\django\core\handlers\exception.py", line 34, in inner
    response = get_response(request)
  File "C:\Users\anton\OneDrive\Documents\django\karate-project-2.2\venv\lib\site-packages\django\core\handlers\base.py", line 115, in _get_response
    response = self.process_exception_by_middleware(e, request)
  File "C:\Users\anton\OneDrive\Documents\django\karate-project-2.2\venv\lib\site-packages\django\core\handlers\base.py", line 113, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "C:\Users\anton\OneDrive\Documents\django\karate-project-2.2\venv\lib\site-packages\django\views\decorators\csrf.py", line 54, in wrapped_view
    return view_func(*args, **kwargs)
  File "C:\Users\anton\OneDrive\Documents\django\karate-project-2.2\venv\lib\site-packages\django\views\generic\base.py", line 71, in view
    return self.dispatch(request, *args, **kwargs)
  File "C:\Users\anton\OneDrive\Documents\django\karate-project-2.2\venv\lib\site-packages\rest_framework\views.py", line 505, in dispatch
    response = self.handle_exception(exc)
  File "C:\Users\anton\OneDrive\Documents\django\karate-project-2.2\venv\lib\site-packages\rest_framework\views.py", line 465, in handle_exception
    self.raise_uncaught_exception(exc)
  File "C:\Users\anton\OneDrive\Documents\django\karate-project-2.2\venv\lib\site-packages\rest_framework\views.py", line 476, in raise_uncaught_exception
    raise exc
  File "C:\Users\anton\OneDrive\Documents\django\karate-project-2.2\venv\lib\site-packages\rest_framework\views.py", line 502, in dispatch
    response = handler(request, *args, **kwargs)
  File "C:\Users\anton\OneDrive\Documents\django\karate-project-2.2\karate2\animals\api\views.py", line 109, in get
    return Response(serializer.data)
  File "C:\Users\anton\OneDrive\Documents\django\karate-project-2.2\venv\lib\site-packages\rest_framework_gis\serializers.py", line 20, in data
    return super(ListSerializer, self).data
  File "C:\Users\anton\OneDrive\Documents\django\karate-project-2.2\venv\lib\site-packages\rest_framework\serializers.py", line 260, in data
    self._data = self.to_representation(self.instance)
  File "C:\Users\anton\OneDrive\Documents\django\karate-project-2.2\venv\lib\site-packages\rest_framework_gis\serializers.py", line 28, in to_representation
    ("features", super(GeoFeatureModelListSerializer, self).to_representation(data))
  File "C:\Users\anton\OneDrive\Documents\django\karate-project-2.2\venv\lib\site-packages\rest_framework\serializers.py", line 677, in to_representation
    return [
  File "C:\Users\anton\OneDrive\Documents\django\karate-project-2.2\venv\lib\site-packages\rest_framework\serializers.py", line 678, in <listcomp>
    self.child.to_representation(item) for item in iterable
  File "C:\Users\anton\OneDrive\Documents\django\karate-project-2.2\venv\lib\site-packages\rest_framework_gis\serializers.py", line 116, in to_representation
    feature["geometry"] = field.to_representation(geo_value)
  File "C:\Users\anton\OneDrive\Documents\django\karate-project-2.2\venv\lib\site-packages\rest_framework_gis\fields.py", line 101, in to_representation
    value = super(GeometrySerializerMethodField, self).to_representation(value)
  File "C:\Users\anton\OneDrive\Documents\django\karate-project-2.2\venv\lib\site-packages\rest_framework\fields.py", line 1905, in to_representation
    return method(value)
  File "C:\Users\anton\OneDrive\Documents\django\karate-project-2.2\karate2\animals\api\serializers.py", line 61, in get_polygon
    return obj.hexgrid_10km2.polygon
AttributeError: 'dict' object has no attribute 'hexgrid_10km2'

更新 修改的代码。我按回复而不是 Hexgrid 过滤的原因是因为用户可以为同一个动物做出多个回复。所以我需要过滤用户对特定动物的最新回复。我知道 .values() 不是用于分组的，但我还能怎么做呢？我考虑过按十六进制网格进行分组，但失败了，因为甚至查询每个用户都得到了第一个回复，我花了很长时间才弄清楚。

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1 回答 1

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回溯已经告诉您问题：您正在尝试访问字典的属性。该.values()方法使用查询集中实例的字段值创建一个字典，并且您传递给序列化程序的是所有这些值字典的列表而不是普通查询集，因此当它尝试访问一个字段时对于查询集的实例，它会引发异常，因为字典没有属性。您不能将字典传递给序列化程序，它必须接收查询集。

要解决这个问题，您必须.values()从视图中删除，并且您可以将polygon_10km2其用作序列化程序中的字段，因为它是模型的属性，以获得您想要的。

于 2020-04-16T11:06:43.387 回答