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为什么克隆floatfield的这个子类(添加了验证器)会引发异常?

django-models django python

spraff · 技术社区 · 6 年前

我是python和django的新手。

我希望我的模型有范围验证的浮动。从 this answer 我写的是:

class FloatRangeField (FloatField):
    """A FloatField constrained to a given range."""

    def __init__ (self, minimum, maximum, **kwargs):

        minmax = [MinValueValidator (minimum), MaxValueValidator (maximum)]

        print ("\n\t\tFloatRangeField({},{})".format(minimum,maximum)) # (A)
        FloatField.__init__ (self, validators = minmax, **kwargs)
        print ("\t\tFINISHED\n")

这导致了 python3 manage.py migrate ,我把范围缩小到 clone() 打电话。演示:

print ("HERE 1")
tmp1 = FloatRangeField (10, 20)
print ("HERE 2")
tmp2 = FloatRangeField (10, 20)
print ("HERE 3")
tmp3 = tmp1.clone ()      # (B)
print ("HERE 4")

它从第行引发异常 # (B) . 奇怪的是,当这种情况发生时 # (A) 是不印刷的。输出如下:

HERE 1

                FloatRangeField(10,20)
                FINISHED

HERE 2

                FloatRangeField(10,20)
                FINISHED

HERE 3
Traceback (most recent call last):
  File "manage.py", line 15, in <module>
    execute_from_command_line(sys.argv)
  File "/usr/local/lib/python3.5/dist-packages/django/core/management/__init__.py", line 371, in execute_from_command_line
    utility.execute()

[...snip...]

    tmp3 = tmp1.clone ()
  File "/usr/local/lib/python3.5/dist-packages/django/db/models/fields/__init__.py", line 470, in clone
    return self.__class__(*args, **kwargs)
TypeError: __init__() missing 2 required positional arguments: 'minimum' and 'maximum'

也没有印刷出来的怪事 (a) ,这是不和我看到的错误一样 migrate . 如果我把 tmp1=... 塞东西然后跑 迁移 ,回溯如下

Traceback (most recent call last):
  File "/usr/local/lib/python3.5/dist-packages/django/db/migrations/state.py", line 411, in from_model
    fields.append((name, field.clone()))
  File "/usr/local/lib/python3.5/dist-packages/django/db/models/fields/__init__.py", line 470, in clone
    return self.__class__(*args, **kwargs)

[...snip...]

    FloatField.__init__ (self, validators = minmax, **kwargs)
TypeError: __init__() got multiple values for keyword argument 'validators'

为什么会中断,我应该如何实现 FloatRangeField 以便封装最小/最大验证器的拥有?

1 回复 | 直到 6 年前

willeM_ Van Onsem 6 年前

就像写在 documentation on custom model fields :

如果添加新的关键字参数,则需要编写代码将其值放入 kwargs 你自己(…)

所以你也应该增加一个解构主义者。这是必需的,例如要在迁移文件中表示此字段:

class FloatRangeField (FloatField):
    """A FloatField constrained to a given range."""

    def __init__ (self, minimum, maximum, **kwargs):
        self.minimum = minimum
        self.maximum = maximum
        minmax = [MinValueValidator (minimum), MaxValueValidator (maximum)]
        FloatField.__init__ (self, validators = minmax, **kwargs)

    def deconstruct(self):
        result = __, __, __, kwargs = super(FloatRangeField, self).deconstruct()
        kwargs['minimum'] = self.minimum
        kwargs['minimum'] = self.maximum
        del kwargs['validators']
        return result

注意,你最好不要使用 validators = minmax 作为参数,因为这将意味着如果用户将使用 validator 你的参数 FloatRangeField 构造函数将出现参数冲突。

例如,可以追加我们的 minmax 已存在的验证器的验证器,然后当我们想解构它时,从验证程序中弹出这些回溯符:

class FloatRangeField (FloatField):
    """A FloatField constrained to a given range."""

    def __init__ (self, minimum, maximum, **kwargs):
        self.minimum = minimum
        self.maximum = maximum
        old_validators = kwargs.get('validators', [])
        minmax = [MinValueValidator (minimum), MaxValueValidator (maximum)]
        kwargs['validators'] = minmax + old_validators
        FloatField.__init__ (self, **kwargs)


    def deconstruct(self):
        result = __, __, __, kwargs = super(FloatRangeField, self).deconstruct()
        kwargs['minimum'] = self.minimum
        kwargs['minimum'] = self.maximum
        kwargs['validators'] = kwargs['validators'][2:]
        return result

所以我们在这里 deconstruct(..) 函数,删除前两个验证器(我们在 __init__(..) 函数)。