带有 self 实例的 Django 模型方法

Question

我正在尝试将一些功能逻辑移至模型的方法中(而不是 View 中)，我认为它属于该位置:

class Spans(models.Model):
    snow = models.IntegerField()
    wind = models.IntegerField()
    exposure = models.CharField(max_length=1)
    module_length = models.IntegerField()
    max_roof_angle = models.IntegerField()
    building_height = models.IntegerField()
    importance_factor = models.IntegerField()
    seismic = models.DecimalField(max_digits=4, decimal_places=2)
    zone = models.IntegerField()
    profile = models.CharField(max_length=55)
    tilt_angle = models.IntegerField()
    span = models.DecimalField(max_digits=18, decimal_places=15)

    def get_spans(self, snow_load, wind_speed, module_length):
        """
        Function to get spans.
        """
        spans = self.objects.filter(
            snow=snow_load,
            wind=wind_speed,
            exposure='B',
            module_length__gte=module_length,
            max_roof_angle=45,
            building_height=30,
            importance_factor=1,
            seismic=1.2,
            zone=1,
            profile='worst'
        ).order_by('snow', 'module_length', 'span')
        return spans

但是，我有点不确定如何调用它。在外壳中我尝试过:

>>> possible_spans = Spans.get_spans(0, 85, 54)

或

>>> possible_spans = Spans.get_spans(Spans, 0, 85, 54)

但我收到错误:

TypeError: unbound method get_spans() must be called with Spans instance as first argument (got int instance instead) 

或

TypeError: unbound method get_spans() must be called with Spans instance as first argument (got ModelBase instance instead)  

我知道我在这里遗漏了 python 逻辑中的一些基本内容，但我不确定它是什么。

任何帮助将不胜感激。

Answer 1

方法需要使用实例来调用，因为方法调用将其作为默认的 self 参数。例如，

instance = Spans.objects.get(id=1)
instance.get_spans(0, 85, 54)

或者如果您想使用类本身进行调用。您必须手动传递实例

instance = Spans.objects.get(id=1)
Spans.get_spans(instance, 0, 85, 54)

更新:您正在寻找的内容可以使用静态方法来实现

@staticmethod
def get_spans(snow_load, wind_speed, module_length):
        """
        Function to get spans.
        """
        spans = Spans.objects.filter(
            snow=snow_load,
            wind=wind_speed,
            exposure='B',
            module_length__gte=module_length,
            max_roof_angle=45,
            building_height=30,
            importance_factor=1,
            seismic=1.2,
            zone=1,
            profile='worst'
        ).order_by('snow', 'module_length', 'span')
        return spans

现在你可以直接做，

Spans.get_spans(0, 85, 54)