Django 按计数和分组

我想计算

车号

字段中的记录数，按

国家分组

我的模特

class country(models.Model):
    country_name = models.CharField(max_length=50, blank=True, default="none")
    volgorde = models.PositiveIntegerField(blank=True, null=True)
    def __str__(self):
        return self.country_name

class car(models.Model):
    car_number = models.CharField(verbose_name='VIN',max_length=11,unique=True,blank=False ,validators=[numeric])
    car_country = models.ForeignKey('country', verbose_name='Country',blank=True, null=True, default=1, on_delete=models.PROTECT)

    def __str__(self):
        return (self.car_number)

    def get_absolute_url(self):
        return reverse("car:list", kwargs={"id":self.id})

    class Meta:
        ordering = ["-car_number"]

我的观点

class CarViewSet(viewsets.ModelViewSet):
    queryset =  car.objects.only('car_country').select_related('car_country')
    serializer_class = CarSerializer


class CountrySerializer(serializers.ModelSerializer):
class Meta:
    model = country
    fields = ('country_name',)

class CarSerializer(serializers.ModelSerializer): 
    car_country = CountrySerializer()

    class Meta:
        model = car
        fields = ('car_number','car_country',)

我现在得到的结果如下：

[
    {
        "car_number": "45678",
        "car_country": {
            "country_name": "Europe/UK"
        }
    },
    {
        "car_number": "3333333",
        "car_country": {
            "country_name": "Europe / Netherlands"
        }
    },
    {
        "car_number": "11111111111",
        "car_country": {
            "country_name": "Europe/UK"
        }
    }
]

你的类名应该以大写字母开头

要返回包含相关
车号数量的国家/地区列表，请首先向您的车型添加以下内容：

class Car(models.Model):
    car_number = models.CharField(verbose_name='VIN',max_length=11,unique=True,blank=False ,validators=[numeric])
    car_country = models.ForeignKey('Country', verbose_name='Country',blank=True, null=True, default=1, on_delete=models.PROTECT, related_name='cars')

from django.db.models import Count

class CarViewSet(viewsets.ModelViewSet):
    queryset =  Country.objects.all().annotate(car_amount=Count('cars')).order_by('-car_amount')
    serializer_class = CountrySerializer

class CountrySerializer(serializers.ModelSerializer):
    count_cars = serializers.SerializerMethodField(read_only=True)

    def get_count_cars(model):
        return model.cars.all().count()

    class Meta:
        model = Country
        fields = ('country_name' 'count_cars',)

然后，您可以在视图中的查询中使用and，如下所示：

class Car(models.Model):
    car_number = models.CharField(verbose_name='VIN',max_length=11,unique=True,blank=False ,validators=[numeric])
    car_country = models.ForeignKey('Country', verbose_name='Country',blank=True, null=True, default=1, on_delete=models.PROTECT, related_name='cars')

from django.db.models import Count

class CarViewSet(viewsets.ModelViewSet):
    queryset =  Country.objects.all().annotate(car_amount=Count('cars')).order_by('-car_amount')
    serializer_class = CountrySerializer

class CountrySerializer(serializers.ModelSerializer):
    count_cars = serializers.SerializerMethodField(read_only=True)

    def get_count_cars(model):
        return model.cars.all().count()

    class Meta:
        model = Country
        fields = ('country_name' 'count_cars',)

为了获得正确的输出，我们使用a获取特定
国家的
汽车
对象的计数，如下所示：

class Car(models.Model):
    car_number = models.CharField(verbose_name='VIN',max_length=11,unique=True,blank=False ,validators=[numeric])
    car_country = models.ForeignKey('Country', verbose_name='Country',blank=True, null=True, default=1, on_delete=models.PROTECT, related_name='cars')

from django.db.models import Count

class CarViewSet(viewsets.ModelViewSet):
    queryset =  Country.objects.all().annotate(car_amount=Count('cars')).order_by('-car_amount')
    serializer_class = CountrySerializer

class CountrySerializer(serializers.ModelSerializer):
    count_cars = serializers.SerializerMethodField(read_only=True)

    def get_count_cars(model):
        return model.cars.all().count()

    class Meta:
        model = Country
        fields = ('country_name' 'count_cars',)

输出应如下所示：

[
    {
        "country_name": "Europe/UK",
        "count_cars": 10
    },
    {
        "country_name": "Netherlands",
        "count_cars": 6
    },
    {
        "country_name": "Belgium",
        "count_cars": 3
    },
]

如果希望输出升序而不是降序，请从
订单中删除
-
。\u by（）

根据车辆数量降序排列：

Country.objects.all（）.annotation（car\u amount=Count（'cars'））.order\u by（'-car\u amount'）

基于车辆数量的升序：

Country.objects.all（）.annotation（car\u amount=Count（'cars'））.order\u by（'car\u amount'）

你的类名应该以大写字母开头

要返回包含相关
车号数量的国家/地区列表，请首先向您的车型添加以下内容：

class Car(models.Model):
    car_number = models.CharField(verbose_name='VIN',max_length=11,unique=True,blank=False ,validators=[numeric])
    car_country = models.ForeignKey('Country', verbose_name='Country',blank=True, null=True, default=1, on_delete=models.PROTECT, related_name='cars')

from django.db.models import Count

class CarViewSet(viewsets.ModelViewSet):
    queryset =  Country.objects.all().annotate(car_amount=Count('cars')).order_by('-car_amount')
    serializer_class = CountrySerializer

class CountrySerializer(serializers.ModelSerializer):
    count_cars = serializers.SerializerMethodField(read_only=True)

    def get_count_cars(model):
        return model.cars.all().count()

    class Meta:
        model = Country
        fields = ('country_name' 'count_cars',)

然后，您可以在视图中的查询中使用and，如下所示：

class Car(models.Model):
    car_number = models.CharField(verbose_name='VIN',max_length=11,unique=True,blank=False ,validators=[numeric])
    car_country = models.ForeignKey('Country', verbose_name='Country',blank=True, null=True, default=1, on_delete=models.PROTECT, related_name='cars')

from django.db.models import Count

class CarViewSet(viewsets.ModelViewSet):
    queryset =  Country.objects.all().annotate(car_amount=Count('cars')).order_by('-car_amount')
    serializer_class = CountrySerializer

class CountrySerializer(serializers.ModelSerializer):
    count_cars = serializers.SerializerMethodField(read_only=True)

    def get_count_cars(model):
        return model.cars.all().count()

    class Meta:
        model = Country
        fields = ('country_name' 'count_cars',)

为了获得正确的输出，我们使用a获取特定
国家的
汽车
对象的计数，如下所示：

class Car(models.Model):
    car_number = models.CharField(verbose_name='VIN',max_length=11,unique=True,blank=False ,validators=[numeric])
    car_country = models.ForeignKey('Country', verbose_name='Country',blank=True, null=True, default=1, on_delete=models.PROTECT, related_name='cars')

from django.db.models import Count

class CarViewSet(viewsets.ModelViewSet):
    queryset =  Country.objects.all().annotate(car_amount=Count('cars')).order_by('-car_amount')
    serializer_class = CountrySerializer

class CountrySerializer(serializers.ModelSerializer):
    count_cars = serializers.SerializerMethodField(read_only=True)

    def get_count_cars(model):
        return model.cars.all().count()

    class Meta:
        model = Country
        fields = ('country_name' 'count_cars',)

输出应如下所示：

[
    {
        "country_name": "Europe/UK",
        "count_cars": 10
    },
    {
        "country_name": "Netherlands",
        "count_cars": 6
    },
    {
        "country_name": "Belgium",
        "count_cars": 3
    },
]

如果希望输出升序而不是降序，请从
订单中删除
-
。\u by（）

根据车辆数量降序排列：

Country.objects.all（）.annotation（car\u amount=Count（'cars'））.order\u by（'-car\u amount'）

基于车辆数量的升序：

Country.objects.all（）.annotation（car\u amount=Count（'cars'））.order\u by（'car\u amount'）
您的车型是什么样子的？您好，我添加了车型谢谢。我真的不确定你想要的输出是什么。你想精确计算哪些字段？我修改了我的问题。结果应该是一个国家（按顺序）和（计数）车号的列表。请参阅我的更新答案您的车型是什么样子的？嗨，Stevy，我添加了车型谢谢。我真的不确定你想要的输出是什么。你想精确计算哪些字段？我修改了我的问题。结果应该是一个国家列表（按顺序排列）和（计数）汽车号码。请参阅我的更新答案