Question

我有这三个类：

class Vehicle(models.Model):
     stock_number = models.CharField(max_length=6)
     vin = models.CharField(max_length=17)
     year = models.ForeignKey(Year)
     ... (several other fields declared here)

class VehicleMileage(models.Model):
    vehicle = models.ForeignKey(Vehicle)
    odometer_reading = models.PositiveIntegerField()
    date_time_added = models.DateTimeField(default=datetime.today, editable=False)

class VehicleMileage(models.Model):
    vehicle = models.ForeignKey(Vehicle)
    price = models.PositiveIntegerField()
    date_time_added = models.DateTimeField(default=datetime.today, editable=False)

我想要做的是从所有类别中获取所有车辆的最新里程和价格，以及所有这些在一个查询中。目前我正在分别获取所有这三个，然后将我想要的内容插入到字典项中以供模板使用，如下所示：

vehicle_list = Vehicle.objects.all().values('vin', 'stock_number', 'year__year')
vehicles = []

for vehicle in vehicle_list:
    lst = {}
    latest_mileage = VehicleMileage.objects.filter(vehicle__stock_number =
                        stock_number).values('odometer_reading').order_by(
                        '-date_time_added')[0]
    latest_price = VehiclePrice.objects.filter(vehicle__stock_number = 
                        stock_number).values('price').order_by(
                        '-date_time_added')[0]
    lst['stock_number'] = vehicle['stock_number']
    lst['year'] = vehicle['year__year']
    lst['vin'] = vehicle['vin']
    lst['mileage'] = latest_mileage['odometer_reading']
    lst['price'] = latest_price['price']

    vehicles.append(lst)

有没有更好的方法可以检索我想要的内容并运行最少量的查询？目前上述代码需要大约100个查询。

Answer 1

django orm中有一些名为reverse relationship的东西。您可以在此案例vehiclemileage中使用模型的小写名称，并使用vehicleprice模型使用Vehicle来获取结果集。

这是查询的外观：

vehicles_with_latest_mileage_price = Vehicle.objects.values('vehiclemileage__odometer_reading','vehicleprice__price','vin','stock_number','year__year').order_by('-vehiclemileage__date_time_added','-vehicleprice__date_time_added')

这应该返回具有相关价格和里程数的最新车辆，从而导致一个查询并返回一个数据集。

抱歉，您必须滚动查看整个查询。

从每个记录的其他两个表中获取最新条目

1 个答案: