问如何设置django模型字段值以根据不同模型中其他字段的值自动计算值

EN

class Model1(models.Model):
    First = models.IntegerField()
    Second = models.IntegerField()

class Model2(models.Model):
    Model1 = models.ForeignKey(Model1, on_delete=models.SET_NULL)
    Sum = models.IntegerField()

def saveSum(request):
    first = 5
    second = 6
    model1 = Model1(first=first,second=second)
    model1.save()
    
    #then sum the values and save it to the second model
    sum = first + second
    model2 = Model2(Model1=model1,sum=sum)
    model2.save()