自例如

Question

我試圖將一些功能邏輯到模型的方法（而不是在視圖）的Django模型的方法，在這裏我認爲它屬於：

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 

不過，我有點不確定如何稱它。在shell我曾嘗試：

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

或

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

，但我得到一個錯誤：

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) 

我知道我失去了一些東西根本在這裏的Python邏輯，但我不知道這是什麼。

任何幫助將不勝感激。

Answer 1

方法需要與實例一起調用，因爲方法調用使其成爲默認的自我參數。例如，

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

或者如果你想使用類本身來調用。你將不得不通過實例手動

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

更新： 什麼你正在尋找可以使用靜態方法

@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 

現在你可以直接做來實現，

Spans.get_spans(0, 85, 54)