Django电力计算应用开发遇KeyError: 'transformer'问题求助

问题背景 #

正在开发一款基于Django的电力公式计算应用，需求是在计算页面输入变量值后，跳转至结果页面查看计算结果，需实现模块间关联以获取对应数值。开发过程中遇到KeyError: 'transformer'错误，触发位置为CalculationView的post方法中transformer = data['transformer']行。尝试修改CalculationForm的fields字段添加/移除'transformer'，问题未解决。

相关代码 #

views.py

class CalculationView(View):
    def get(self, request):
        transformers = Transformer.objects.all()
        
        form = CalculationForm()
        return render(request, 'calculation_form.html', {'form': form})

    def post(self, request):
        form = CalculationForm(request.POST)

        if form.is_valid():
            data = form.cleaned_data
            
            LowVoltageLineCurrent = data['Power'] / (data['HighVoltage'] * math.sqrt(3))
            HighVoltageLineCurrent = data['Power'] / (data['LowVoltage'] * math.sqrt(3))

            if data['LVconnection'].lower() == 'y':
                LowVoltagePhaseCurrent = LowVoltageLineCurrent
            elif data['LVconnection'].lower() == 'd':
                LowVoltagePhaseCurrent = LowVoltageLineCurrent / math.sqrt(3)
            else:
                LowVoltagePhaseCurrent = None

            if data['HVconnection'].lower() == 'y':
                HighVoltagePhaseCurrent = HighVoltageLineCurrent
            elif data['HVconnection'].lower() == 'd':
                HighVoltagePhaseCurrent = HighVoltageLineCurrent / math.sqrt(3)
            else:
                HighVoltagePhaseCurrent = None

            transformer = data['transformer']
            
            result = Result.objects.create(
                Power=data['Power'],
                HighVoltage=data['HighVoltage'],
                LowVoltage=data['LowVoltage'],
                LowVoltageLineCurrent=LowVoltageLineCurrent,
                HighVoltageLineCurrent=HighVoltageLineCurrent,
                LVconnection=data['LVconnection'],
                HVconnection=data['HVconnection'],
                LowVoltagePhaseCurrent=LowVoltagePhaseCurrent,
                HighVoltagePhaseCurrent=HighVoltagePhaseCurrent,
                transformer=transformer,
                user=request.user
            )

            return redirect('results', pk=result.pk)

        return render(request, 'calculation_form.html', {'form': form})


class ResultsView(View):
    def get(self, request, pk):
        result = Result.objects.get(pk=pk, user=request.user)
        return render(request, 'results.html', {'result': result})

models.py

from django.db import models
from django.utils import timezone
from django.contrib.auth.models import User

class Transformer(models.Model):
    LV_CHOICES = [('D', 'D'),('Y', 'Y'),]
    HV_CHOICES = [('D', 'D'),('Y', 'Y'),]

    user = models.ForeignKey(User, on_delete=models.PROTECT)
    name = models.CharField(max_length=50)
    Power = models.IntegerField(null=False, blank=False)
    HighVoltage = models.IntegerField()
    HVconnection = models.CharField(max_length=1, choices=HV_CHOICES, default='D', db_index=True)
    LowVoltage = models.IntegerField()
    LVconnection = models.CharField(max_length=1, choices=LV_CHOICES, default='D', db_index=True)
    created_at = models.DateTimeField(default=timezone.now)
    
    def __str__(self):
        return self.name


class Result(models.Model):
    transformer = models.ForeignKey(Transformer, on_delete=models.CASCADE, related_name="transformer_result")
    HighVoltageLineCurrent = models.FloatField()    
    HighVoltagePhaseCurrent = models.FloatField(null=True, blank=True)
    LowVoltageLineCurrent = models.FloatField()
    LowVoltagePhaseCurrent = models.FloatField()

forms.py

from django import forms
from .models import Transformer

class CalculationForm(forms.ModelForm):
    class Meta:
        model=Transformer
        fields='__all__'

错误信息 #

line 52, in post
    transformer = data['transformer']
~~~~^^^^^^^^^^^^^^^
KeyError: 'transformer'

错误原因 #

1. CalculationForm基于Transformer模型创建，但Transformer模型本身不存在transformer字段，因此表单验证通过后，cleaned_data字典中不会有该键，直接访问会触发KeyError。
2. 业务逻辑需要将Result关联到Transformer实例，但当前表单设计与需求不匹配：要么需用户选择已有变压器，要么需先创建新变压器再关联结果。

解决方案 #

方案一：用户选择已有变压器进行计算 #

若需求是让用户从已存在的变压器中选择一个，使用其参数完成计算：

1. 修改forms.py，创建包含变压器选择的表单：

from django import forms
from .models import Transformer

class CalculationForm(forms.Form):
    transformer = forms.ModelChoiceField(queryset=Transformer.objects.all(), label="选择变压器")
    # 若需用户自定义参数，可添加对应字段，例如：
    # Power = forms.IntegerField(label="功率")
    # HighVoltage = forms.IntegerField(label="高压")

2. 修改views.py的CalculationView：

class CalculationView(View):
    def get(self, request):
        form = CalculationForm()
        return render(request, 'calculation_form.html', {'form': form})

    def post(self, request):
        form = CalculationForm(request.POST)

        if form.is_valid():
            data = form.cleaned_data
            # 获取选中的变压器实例
            transformer = data['transformer']
            
            # 使用变压器自带参数计算
            LowVoltageLineCurrent = transformer.Power / (transformer.HighVoltage * math.sqrt(3))
            HighVoltageLineCurrent = transformer.Power / (transformer.LowVoltage * math.sqrt(3))

            if transformer.LVconnection.lower() == 'y':
                LowVoltagePhaseCurrent = LowVoltageLineCurrent
            elif transformer.LVconnection.lower() == 'd':
                LowVoltagePhaseCurrent = LowVoltageLineCurrent / math.sqrt(3)
            else:
                LowVoltagePhaseCurrent = None

            if transformer.HVconnection.lower() == 'y':
                HighVoltagePhaseCurrent = HighVoltageLineCurrent
            elif transformer.HVconnection.lower() == 'd':
                HighVoltagePhaseCurrent = HighVoltageLineCurrent / math.sqrt(3)
            else:
                HighVoltagePhaseCurrent = None

            result = Result.objects.create(
                Power=transformer.Power,
                HighVoltage=transformer.HighVoltage,
                LowVoltage=transformer.LowVoltage,
                LowVoltageLineCurrent=LowVoltageLineCurrent,
                HighVoltageLineCurrent=HighVoltageLineCurrent,
                LVconnection=transformer.LVconnection,
                HVconnection=transformer.HVconnection,
                LowVoltagePhaseCurrent=LowVoltagePhaseCurrent,
                HighVoltagePhaseCurrent=HighVoltagePhaseCurrent,
                transformer=transformer,
                user=request.user
            )

            return redirect('results', pk=result.pk)

        return render(request, 'calculation_form.html', {'form': form})

方案二：用户输入参数创建新变压器，再关联结果 #

若需求是让用户输入变压器参数，先创建新Transformer实例，再将计算结果关联到该实例：

1. 修改views.py的CalculationView的post方法：

def post(self, request):
    form = CalculationForm(request.POST)

    if form.is_valid():
        # 创建并保存Transformer实例
        transformer = form.save(commit=False)
        transformer.user = request.user  # 绑定当前用户
        transformer.save()
        
        data = form.cleaned_data
        
        LowVoltageLineCurrent = data['Power'] / (data['HighVoltage'] * math.sqrt(3))
        HighVoltageLineCurrent = data['Power'] / (data['LowVoltage'] * math.sqrt(3))

        if data['LVconnection'].lower() == 'y':
            LowVoltagePhaseCurrent = LowVoltageLineCurrent
        elif data['LVconnection'].lower() == 'd':
            LowVoltagePhaseCurrent = LowVoltageLineCurrent / math.sqrt(3)
        else:
            LowVoltagePhaseCurrent = None

        if data['HVconnection'].lower() == 'y':
            HighVoltagePhaseCurrent = HighVoltageLineCurrent
        elif data['HVconnection'].lower() == 'd':
            HighVoltagePhaseCurrent = HighVoltageLineCurrent / math.sqrt(3)
        else:
            HighVoltagePhaseCurrent = None

        result = Result.objects.create(
            Power=data['Power'],
            HighVoltage=data['HighVoltage'],
            LowVoltage=data['LowVoltage'],
            LowVoltageLineCurrent=LowVoltageLineCurrent,
            HighVoltageLineCurrent=HighVoltageLineCurrent,
            LVconnection=data['LVconnection'],
            HVconnection=data['HVconnection'],
            LowVoltagePhaseCurrent=LowVoltagePhaseCurrent,
            HighVoltagePhaseCurrent=HighVoltagePhaseCurrent,
            transformer=transformer,
            user=request.user
        )

        return redirect('results', pk=result.pk)

    return render(request, 'calculation_form.html', {'form': form})

2. 修改forms.py排除user字段：

class CalculationForm(forms.ModelForm):
    class Meta:
        model=Transformer
        fields=['name', 'Power', 'HighVoltage', 'HVconnection', 'LowVoltage', 'LVconnection']

额外注意事项 #

当前Result模型缺少关联计算所需的字段，需补充：

class Result(models.Model):
    transformer = models.ForeignKey(Transformer, on_delete=models.CASCADE, related_name="transformer_result")
    Power = models.IntegerField()
    HighVoltage = models.IntegerField()
    LowVoltage = models.IntegerField()
    LVconnection = models.CharField(max_length=1)
    HVconnection = models.CharField(max_length=1)
    HighVoltageLineCurrent = models.FloatField()    
    HighVoltagePhaseCurrent = models.FloatField(null=True, blank=True)
    LowVoltageLineCurrent = models.FloatField()
    LowVoltagePhaseCurrent = models.FloatField()
    user = models.ForeignKey(User, on_delete=models.CASCADE)

内容的提问来源于stack exchange，提问作者David D