反向外键查找

Question

#models.py
class Orders(models.Model):
    orderid = models.IntegerField(db_column='orderID', primary_key=True) 
    createdate = models.DateField(db_column='createDate', blank=True, null=True) 
    pickupdate = models.DateField(db_column='pickupDate', blank=True, null=True)  
    returndate = models.DateField(db_column='returnDate', blank=True, null=True)  
    pickupstore = models.ForeignKey(Branch, models.DO_NOTHING, db_column='pickupStore', blank=True, null=True,related_name = 'pickupstore')  
    returnstore = models.ForeignKey(Branch, models.DO_NOTHING, db_column='returnStore', blank=True, null=True,related_name = 'returnstore') 
    rentedvehicle = models.ForeignKey('Vehicles', models.DO_NOTHING, db_column='rentedVehicle', blank=True, null=True)  
    customer = models.ForeignKey(Customer, models.DO_NOTHING, db_column='customer', blank=True, null=True)


class Vehicles(models.Model):
    vehicleid = models.IntegerField(db_column='vehicleID', primary_key=True)  
    make = models.CharField(max_length=45, blank=True, null=True)
    model = models.CharField(max_length=45, blank=True, null=True)
    series = models.CharField(max_length=45, blank=True, null=True)


#views.py
def topcar(request):
    topCar = Vehicles.objects.filter(orders__pickupstore__state = request.POST['state']).annotate(num_car =Count('orders')).order_by('-num_car')[:20]
    return render(request, 'web/topcar.html',{'topCar':topCar, 'state':request.POST['state'])




#topcar.html
{% for car in topCar %}
   <tr>
      <td>{{car.make}} {{car.model}} {{car.series}}  {{car.year}}</td>
      <td>{{car.seatcapacity}}</td>
      <td>{{the latest car return store}}</td>
   </tr>
{% endfor %}

在views.py中，topCar变量是在Orders模型中具有高订单的前20辆车辆（在车辆模型中）的列表.Orders模型中的字段租赁车辆是外键是指车辆模型。

我想在topCar变量中为每辆车获取最新的returnstore（Orders模型中的一个字段）。我希望它显示在topCar.html的{{最新汽车返回商店}}中

我该怎么办？

我发现我可以这样做：

Orders.objects.filter(rentedvehicle = car.vehicleid).latest('returndate').returnstore

获取最新的车辆返回商店。但是，我不知道如何使用它来获得我想要的结果。

Answer 1

您只能在Django模板中使用简单的查找逻辑，因此您无法在那里进行latest('returndate')过滤。

相反，您可以向Vehicle模型添加方法以获取最新订单：

class Vehicles(models.Model):
    vehicleid = models.IntegerField(db_column='vehicleID', primary_key=True)  
    make = models.CharField(max_length=45, blank=True, null=True)
    model = models.CharField(max_length=45, blank=True, null=True)
    series = models.CharField(max_length=45, blank=True, null=True)

    def latest_order(self):
        return self.orders_set.latest('returndate')

然后，您应该能够将模板修改为：

{% for car in topCar %}
   <tr>
      <td>{{car.make}} {{car.model}} {{car.series}}  {{car.year}}</td>
      <td>{{car.seatcapacity}}</td>
      <td>{{car.latest_order.returnstore}}</td>
   </tr>
{% endfor %}