ForeignKey显示

情景：Model 外键了user，后台想在列表里显示username
list_display = ("username", "xx", ...)
def username(self, obj):
    return obj.user.username
username.short_description = "Show User's username."

ForeignKey所在表字段过多

Django的admin会默认生成一个可选择外键的下拉列表，也就意味着它会SELECT整张表，如果这个外键表过大会造成浏览器迟迟无法刷新

1. 解决方法一：
   取消下拉列表 ==> admin里加个字段

raw_id_fields = ('foreignkey', ...)

2. 解决方法二：
   减小下拉列表的搜索范围 ==> 重写form

省市县，三级分开
class xxxForm(forms.ModelForm):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

        self.fields['province'].queryset = Areas.objects.filter(LevelType=1)
        self.fields['city'].queryset = Areas.objects.filter(LevelType=2)
        self.fields['district'].queryset = Areas.objects.filter(LevelType=3)

    class Meta:
        model = BusinessCircle
        fields = '__all__'

3. 解决方法三：
   一劳永逸的定制formfield_for_foreignkey方法，新写插件ChainedWidget

该方法原封装在BaseModelAdmin下
def formfield_for_foreignkey(self, db_field, request, **kwargs):
    if db_field.name in ["province", "city", "district"]:
        return db_field.formfield(widget=ChainedWidget())
    return super().formfield_for_foreignkey(
        db_field, request, **kwargs)

但是具体的呢我还没看懂……等研究完再更新