如果我知道第一个字段值，如何从模型中获取另一个字段值? [英] How to get another field value from model if I know first field value?

问题描述

我正在尝试学习django并在访问模型时遇到问题.

I am trying to learn django and faced problem accessing models.

我在 models.py 中有一个看起来像这样的模型:

I have model in models.py that look like this:

class Countries(models.Model):

    Country = models.CharField(max_length=200)

    PPP = models.DecimalField(max_digits=15, decimal_places=10)

    def __str__(self):
        return self.Country

现在在 views.py 中，我想根据用户输入进行一些计算.用户将从第一个字段( Country )中选择值，我需要根据该值找到第二个字段值( PPP ).

Now in views.py I want to make some calculations based on user input. User will choose value from first field (Country) and I need to find second field value (PPP) based on that.

这意味着我的数据结构如下:

It means that I have data structured something like that:

Country   | PPP
----------------
Lithuania | 0.45
Germany   | 0.86
Estonia   | 0.55
Spain     | 0.77

因此，我将了解国家/地区，并且需要访问其PPP.我该怎么办?

So I will know country and I will need to access its PPP. How should I do it?

由于我尝试了各种解决方案，所以给了我一个错误.

Because various solutions I tried gives me an error.

我不满意的最新解决方案:

Lats solutions I tired:

pVal = str(form.cleaned_data['Country'])
country = Countries.objects.first()
pValKof = getattr(country, pVal) 

根据我的研究，我觉得我应该在解决方案附近，但我只是无法完全理解 getattr .也许还有其他方法可以实现这一目标?

Based on my research I feel I should be somewhere near the solution, but I just can't understand getattr completely. Or maybe there is some other way to achieve this?

这是我的 forms.py

class PGPskaiciuokle(forms.Form):

    country = forms.ModelChoiceField(queryset=Countries.objects.all(),
                                       label="Choose country")

    def clean_country(self):
        country = self.cleaned_data['country']
        return country

推荐答案

更改了我的解决方案，因为我错过了Form字段是ModelChoiceField的事实

Changed my solution, because I missed the fact that the Form's field was a ModelChoiceField

代替:

pVal = str(form.cleaned_data['Country'])
country = Countries.objects.first()
pValKof = getattr(country, pVal) 

执行此操作:

country = form.cleaned_data['Country']
ppp = country.PPP

此外:

1. Python中的属性应以小写字母开头，类以大写字母开头，因此，使用Country和ppp代替Country和PPP(不确定ppp代表什么，使用更多的内容不会有什么害处描述性名称)

1. Properties in Python should start with a lowercase letter, classes with an uppercase letter, so instead of Country and PPP, use country and ppp (Not sure what ppp stands for, it wouldn't hurt to use a more descriptive name)

型号名称应为单数.因此，请使用国家代替

A model name should be singular. So instead of Countries, use Country

国家(地区)属性可能更具描述性.尝试使用名称代替国家/地区.

The property Country could be more descriptive. Try using name instead of country.

我会为每个国家/地区选择一个唯一的名称.

I would opt for a unique name for each country.

所以要稍微整理一下代码:

So to clean up your code a bit:

class Country(models.Model):

        name = models.CharField(max_length=200, unique=True, null=False)

        ppp = models.DecimalField(max_digits=15, decimal_places=10)

        def __str__(self):
            return self.name

还有

country = form.cleaned_data['country']
ppp = country.PPP

以及表单文件:

class PGPskaiciuokle(forms.Form):

    country = forms.ModelChoiceField(queryset=Country.objects.all(),
                                   label="Choose country")

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