Django 1.5中缺少元类

问题描述

如何在Django 1.5中覆盖模型的元类？我在一些继承自抽象模型的模型上覆盖了元类，所以我可以设置适当的选择。例如

  class BaseModel（models.Model）：
 
 field_with_choices = models.CharField（max_length = 100 ）
 
 class Meta：
 abstract = True 
 
 class MyModelMetaClass（BaseModel .__ metaclass__）：
 def __new __（cls，* args，** kwargs ）
 new_class = super（MyModelMetaClass，cls）.__ new __（cls，* args，** kwargs）
 field = new_class._meta.get_field（'field_with_choices'）
 choices = field。 _choices = [] 
 choices.extend（get_choices（））
 return new_class 
 
 class MyModel（BaseModel）：
 
 __metaclass__ = MyModelMetaClass $ b $但是，当我升级到Django 1.5时，我现在得到错误：
  AttributeError：类型对象'BaseModel'没有属性'__metaclass__'
  
如何在1.5中覆盖模型的元类，否则在模型子类中动态设置字段属性
解决方案
您可以使用内置函数 type  like this：
  class MyModelMetaClass（type（BaseModel））：
 def __new __（cls，* args，** kwargs）：
 new_class = super（MyModelMetaClass，cls）.__ new __（cls，* args，** kwargs）
 field = new_class._meta.get_field （'field_with_choices'）
 choices = field._choices = [] 
 choices.extend（get_choices（））
返回new_class 
  
虽然我看到 type（ModelBase）是类型，所以你基本上可以继承自类型或者可能来自 Model .__ metaclass __ ，这反过来 ModelBase  so  ModelBase 是模型元类架构的顶端（当然类型当然是：D）。
 
 
 
希望它有帮助！
 
How do you override a model's metaclass in Django 1.5? I was overriding the metaclass on some models inheriting from an abstract model so I could set appropriate choices. e.g.
class BaseModel(models.Model):

    field_with_choices = models.CharField(max_length=100)

    class Meta:
        abstract = True

class MyModelMetaClass(BaseModel.__metaclass__):
    def __new__(cls, *args, **kwargs):
        new_class = super(MyModelMetaClass, cls).__new__(cls, *args, **kwargs)
        field = new_class._meta.get_field('field_with_choices')
        choices = field._choices = []
        choices.extend(get_choices())
        return new_class

class MyModel(BaseModel):

    __metaclass__ = MyModelMetaClass
However, when I upgraded to Django 1.5, I now get the error:
AttributeError: type object 'BaseModel' has no attribute '__metaclass__'
How do you override a model's metaclass in 1.5, or otherwise dynamically set field attributes in model subclasses?
 解决方案 
You can use the built-in function type like this:
class MyModelMetaClass(type(BaseModel)):
    def __new__(cls, *args, **kwargs):
        new_class = super(MyModelMetaClass, cls).__new__(cls, *args, **kwargs)
        field = new_class._meta.get_field('field_with_choices')
        choices = field._choices = []
        choices.extend(get_choices())
        return new_class
Although I see that type(ModelBase) is type so you basically could inherit from type or maybe from Model.__metaclass__ which is in turn ModelBase so ModelBase is the top of the Model metaclass architecture (before type of course :D ).
Hope it helps!
                        
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