Django管理员：SORTING list_display字段反向FK聚合

Question

模型站有一个FK到系统。我想在系统 admin更改列表中显示工作站列为列。我已经用下面的代码实现了这一点，但是我很难将'num_stations'列排序。

model.py：

class System(models.Model): 
    pass 

class Station(models.Model): 
    system_info = models.ForeignKey(System) 

admin.py：

class SystemAdmin(admin.ModelAdmin): 
    def num_stations(self, obj): 
     return obj.station_set.count() 

    # num_stations.admin_order_field = ???? 
    num_stations.short_description = 'stations' 

    list_display = (num_stations',) 

成反向关系的普通 'station_set' 的语法似乎并没有在admin_order_field工作，即使其他堆溢出问题一般显示正向移动关系支持 例如

• Django admin: how to sort by one of the custom list_display fields that has no database field
• Can “list_display” in a Django ModelAdmin display attributes of ForeignKey fields?。

Answer 1

感谢Alasdair作为他们的评论，答案在this question正如指出。这里是一个适合我的问题的解决方案：

class SystemAdmin(admin.ModelAdmin): 
    def num_stations(self, obj): 
     return obj.num_stations 

    def get_queryset(self, request): 
     # def queryset(self, request): # For Django <1.6 
     qs = super(SystemAdmin, self).get_queryset(request) 
     # qs = super(CustomerAdmin, self).queryset(request) # For Django <1.6 
     qs = qs.annotate(num_stations=Count('station')) 
     return qs 

    num_stations.admin_order_field = 'num_stations' 
    num_stations.short_description = 'stations' 

    list_display = ('num_stations',)