在调用 save() 之前根据 max_digits 和 decimal_places 属性自动舍入 Django 的 DecimalField

Question

我想在ModelForm中调用save()函数之前，根据max_digits和decimal_places属性自动对Django的DecimalField进行四舍五入。

目前正在使用以下：

• django 1.8
• python 2.7

到目前为止我已经尝试过什么。

https://djangosnippets.org/snippets/10554/

---

models.py

amount = models.DecimalField(max_digits = 19, decimal_places = 2)

views.py

附：将它应用到不同的领域和不同的模型中

data = {"amount" : 100.1234,"name":"John Doe",...}
form = My_form(data)
if form.is_valid(): //the error throws from here.
    form.save()
else:
    raise ValueError(form.errors)

forms.py

我计划清理 clean() 函数中的字段并对所有小数字段进行四舍五入，但是当我尝试打印 raw_data 时，没有“金额字段”。

class My_form(forms.ModelForm):
    Class Meta:
        model = My_model
        fields = ('amount','name')
    def clean(self):
        raw_data = self.cleaned_data
        print(raw_data) //only prints {'name' : 'John Doe'}

Answer 1

您收到错误主要是因为forms.DecimalField 与models.DecimalField 有单独的验证器：

data = {'amount': 1.12345 }

class NormalForm(forms.Form):
    amount = forms.DecimalField(max_digits = 19, decimal_places = 2)

normal_form = NormalForm(data)
normal_form.is_valid()  # returns False
normal_form.cleaned_data  # returns {}

并且forms.DecimalField 默认用于具有models.DecimalField 类字段的模型的表单。你可以这样做：

from django import forms
from django.db import models
from decimal import Decimal

def round_decimal(value, places):
    if value is not None:
        # see https://docs.python.org/2/library/decimal.html#decimal.Decimal.quantize for options
        return value.quantize(Decimal(10) ** -places)
    return value

class RoundingDecimalFormField(forms.DecimalField):
    def to_python(self, value):
        value = super(RoundingDecimalFormField, self).to_python(value)
        return round_decimal(value, self.decimal_places)

class RoundingDecimalModelField(models.DecimalField):
    def to_python(self, value):
        # you could actually skip implementing this
        value = super(RoundingDecimalModelField, self).to_python(value)
        return round_decimal(value, self.decimal_places)

    def formfield(self, **kwargs):
        defaults = { 'form_class': RoundingDecimalFormField }
        defaults.update(kwargs)
        return super(RoundingDecimalModelField, self).formfield(**kwargs)

现在，在您使用models.DecimalField 的任何地方，请改用RoundingDecimalModelField。您在这些模型中使用的任何表单现在也将使用自定义表单字段。

class RoundingForm(forms.Form):
    amount = RoundingDecimalFormField(max_digits = 19, decimal_places = 2)

data = {'amount': 1.12345 }

rounding_form = RoundingForm(data)
rounding_form.is_valid()  # returns True
rounding_form.cleaned_data  # returns {'amount': Decimal('1.12')}

Answer 2

如果您直接分配给模型实例，则无需担心。字段对象会将值量化（四舍五入）到您在模型定义中设置的小数点级别。

如果您处理的是ModelForm，默认DecimalField 将要求任何输入与模型字段的小数点匹配。一般来说，处理这个问题的最简单方法可能是对模型DecimalField 进行子类化，删除特定于小数的验证器并依靠底层转换来量化数据，如下所示：

from django.db.models.fields import DecimalField

class RoundingDecimalField(DecimalField):

    @cached_property
    def validators(self):
        return super(DecimalField, self).validators

    def formfield(self, **kwargs):
        defaults = {
            'max_digits': self.max_digits,
            'decimal_places': 4, # or whatever number of decimal places you want your form to accept, make it a param if you like
            'form_class': forms.DecimalField,
        }
        defaults.update(kwargs)
        return super(RoundingDecimalField, self).formfield(**defaults)

然后在你的模型中：

amount = RoundingDecimalField(max_digits = 19, decimal_places = 2)

（实际上不要将字段类放在与模型相同的字段中，这只是示例。）

这在绝对意义上可能不如定义自定义字段表单正确，这是我的第一个建议，但使用起来更少。

Answer 3

如果您想设置小部件以限制十进制数字输入表单仅使用此代码呈现

from django import forms

class DecimalNumberInput(forms.NumberInput):
    def get_context(self, name, value, attrs):

        context = super().get_context(name, value, attrs)
        try:
            if self.attrs['decimal_places'] and isinstance(self.attrs['decimal_places'], int) :
                context['widget']['value'] = str(round(float(context['widget']['value']),self.attrs['decimal_places']))
        except Exception as e:
            pass
        return context
class NormalForm(forms.Form):
    amount = forms.DecimalField(max_digits = 19, decimal_places = 2 , widget=DecimalNumberInput(attrs={'decimal_places':2}))