python - django 将查询集填充到字典中

Question

我不是很高级的 python 用户，我一直在尝试填充以下内容，但我认为处理 list_choices 是错误的。

class LocationManager(TranslationManager):
    def get_location_list(self, lang_code, site=None):
        # this function is for building a list to be used in the posting process
        # TODO: tune the query to hit database only once
        list_choices = {}
        for parents in self.language(lang_code).filter(country__site=site, parent=None):    
            list_child = ((child.id, child.name) for child in self.language(lang_code).filter(parent=parents))
            list_choices.setdefault(parents).append(list_child)

        return list_choices

在错误下方

>>> 
>>> Location.objects.get_location_list(lang_code='en', site=current_site)
Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/home/mo/Projects/mazban/mazban/apps/listing/geo/models.py", line 108, in get_location_list
    list_choices.setdefault(parents).append(list_child)
AttributeError: 'NoneType' object has no attribute 'append'

Answer 1

那是因为您在setdefault没有第二个参数的情况下使用。None在这种情况下它会返回。

试试这个固定代码：

# this is much more confinient and clearer
from collections import defaultdict

def get_location_list(self, lang_code, site=None):
    # this function is for building a list to be used in the posting process
    # TODO: tune the query to hit database only once
    list_choices = defaultdict(list)
    for parent in self.language(lang_code).filter(country__site=site, parent=None):
        list_child = self.language(lang_code).filter(parent=parent).values_list('id', 'name')
        list_choices[parent].extend(list_child)

    return list_choices