GeoDjango：距离对象不可序列化

Question

我只是在学习 geo-django。我可以从一个点找出所有地方的距离。但是当我.values对带注释的distance字段使用方法时，我得到了

TypeError: Object of type 'Distance' is not JSON serializable

这是我的代码片段

#models.py
import uuid
from django.contrib.gis.db import models
from django.contrib.gis.db.models.functions import Distance
from django.contrib.gis.geos import Point
class PlaceManager(models.GeoManager):
    def get_queryset(self):
        qs = super(PlaceManager, self).get_queryset()
        qs = qs.annotate(
        latitude=models.ExpressionWrapper(models.Func('position', function='ST_X'), output_field=models.FloatField()),
        longitude=models.ExpressionWrapper(models.Func('position', function='ST_Y'), output_field=models.FloatField()),
    )
    return qs.distinct()

    def nearby_places(self, lat, lng):
        p = Point(lat, lng, srid=4326)
        qs = self.get_queryset()
        qs = qs.annotate(
            distance=Distance('position', p)
        )
        return qs.order_by('distance').distinct()


class Place(models.Model):
    id = models.UUIDField(default=uuid.uuid4, editable=False, primary_key=True, db_index=True)
    position = models.PointField()
    address = models.TextField(default=None, null=True, blank=True)
    objects = PlaceManager()

    def __str__(self):
        return '{},{}'.format(self.position.x, self.position.y)

现在我的代码片段是这样的

from rest_framework.views import APIView
from rest_framework import status
from rest_framework.response import Response

class NearbyPlaces(APIView):
    def get(self, request):
        p = Place.objects.nearby_places(30.45, -90.43)
        p = p.values('distance', 'address', 'latitude', 'longitude')
        return Response(p, status=status.HTTP_200_OK)

p这里的值是这样的

<GeoQuerySet [{'distance': Distance(m=7596021.71574835), 'address': 'New York City, New York','latitude': 13.4586, 'longitude': 45.6789}]>

因此，这里需要的一切我是'distance': 7596021.71574835不是'distance': Distance(m=7596021.71574835)

这有什么帮助吗？提前致谢。

Answer 1

还有一个更简单的方法，只需要改变serializer.py中的内容即可：

class CitySerializer(serializers.ModelSerializer):

    distance = serializers.SerializerMethodField()

    def get_distance(self, obj):

        return obj.distance.m

    class Meta:
        model = City
        fields = ('distance')

Answer 2

刚刚找到了一种方法。必须在休息框架中创建一个渲染器类并处理Distance其中的对象。代码片段是这样的。

编码器.py

from rest_framework.utils.encoders import JSONEncoder
from django.contrib.gis.measure import Distance


class CustomJsonEncoderWithDistance(JSONEncoder):
    def default(self, obj):
        if isinstance(obj, Distance):
            print(obj)
            return obj.m
        return super(CustomJsonEncoderWithDistance, self).default(obj)

渲染.py

from rest_framework.renderers import JSONRenderer
from .encoders import CustomJsonEncoderWithDistance


class CustomJsonRenderer(JSONRenderer):
     encoder_class = CustomJsonEncoderWithDistance

设置.py

...
REST_FRAMEWORK = {
    'DEFAULT_RENDERER_CLASSES': (
        'app.renderers.CustomJsonRenderer',
    )
}