Question

我有一个模型，其中Vehicle表具有更多Wheels表。我试图在单个字段中显示车辆和相关“车轮”表中第一个车轮的信息。我已经看到F函数可能有用，但是我找不到正确的配置才能正常工作。这些表通过另一个名为colour的字段关联，该字段在Wheels表中声明为外键。


    class VehicleListView(ListView):
        template_name = 'vehicle.html'
        queryset = Vehicle.objects.all()

        queryset = queryset.annotate(wheel1_name = F('Wheels__wheel_name'))

        def get_context_data(self, **kwargs):
            context = super().get_context_data(**kwargs)
            return context

我想要这行


    queryset = queryset.annotate(wheel1_name = F('Wheels__wheel_name'))

返回每个车辆的第一个车轮名称的列表，以便我可以对其进行迭代并将其显示在表格中。

models.py

class Vehicle(models.Model):
    vehicle_id = models.AutoField(primary_key=True)
    vehicle_name = models.CharField(max_length=100)
    color = models.CharField(max_length=100)

class Wheels(models.Model):
    wheels_id = models.AutoField(primary_key=True)
    color = models.ForeignKey(Vehicle, null=True, on_delete=models.SET_NULL,
                                  db_column='color')
    wheel_name = models.CharField(max_length=100)

Answer 1

所以我稍微更改了代码，设置了数据库，创建了2个Vehicle对象，每个对象有2个相关的Wheels对象，所以总共有4个Wheels对象。

我为某个特定的Wheel对象的第一个相关Vehicle对象添加了queries的函数。

# models.py

class Vehicle(models.Model):
    vehicle_id = models.AutoField(primary_key=True)
    vehicle_name = models.CharField(max_length=100)
    color = models.CharField(max_length=100)

    # this function returns a slice of the resulting queryset which contains
    # the first related Wheels object for each Vehicle object
    def get_first_wheels(self):
        return Wheels.objects.filter(color=self).order_by('wheels_id')[:1]


class Wheels(models.Model):
    wheels_id = models.AutoField(primary_key=True)
    color = models.ForeignKey(Vehicle, null=True, on_delete=models.SET_NULL)
    wheel_name = models.CharField(max_length=100)

我使用Django serializers来序列化数据。为了获得第一个相关的Wheels对象，我使用了SerializerMethodField()，它在get_first_wheels()中调用models.py函数，如下所示：

# serializers.py

class WheelsSerializer(serializers.ModelSerializer):
    class Meta:
        model = Wheels
        fields = ('wheels_id', 'color', 'wheel_name')


class VehicleSerializer(serializers.ModelSerializer):
    first_wheel = serializers.SerializerMethodField(read_only=True)

    def get_first_wheel(self, model):
        qs = model.get_first_wheels()
        return WheelsSerializer(qs, many=True).data

    class Meta:
        model = Vehicle
        fields = ('vehicle_id', 'vehicle_name', 'color', 'first_wheel')

我稍微改变了您的看法，改用ModelViewSet。

# views.py

class VehicleViewSet(viewsets.ModelViewSet):
    serializer_class = VehicleSerializer
    queryset = Vehicle.objects.all()

我去了DefaultRouter()，并用这种方式注册了端点：

# urls.py

from rest_framework import routers
# import ViewSet here

router = routers.DefaultRouter()

router.register(r'vehicles`, views.VehicleViewSet, base_name='vehicle')

然后我运行了以下命令：

manage.py makemigrations
manage.py migrate
manage.py runserver

我创建了2个Vehicle对象，每2个相关的Wheels对象。

当我在浏览器中转到http://127.0.0.1:8000/vehicles/时，它将返回所有Vehicle对象以及它们的第一个相关Wheels对象，如下所示：

[
    {
        "vehicle_id": 1,
        "vehicle_name": "BMW",
        "color": "Blue",
        "first_wheel": [
            {
                "wheels_id": 1,
                "color": 1,
                "wheel_name": "BMW1"
            }
        ]
    },
    {
        "vehicle_id": 2,
        "vehicle_name": "Ferrari",
        "color": "Red",
        "first_wheel": [
            {
                "wheels_id": 3,
                "color": 2,
                "wheel_name": "Ferrari1"
            }
        ]
    }
]

如何用相关模型中的新信息字段注释查询集？

1 个答案: