为何Django模型FloatField改DecimalField后HTML表单无法接收小数？

我原本有一个类型为FloatField的amount字段，将其修改为DecimalField后，执行了makemigrations和migrate命令，成功生成了0002_alter_expense_amount.py文件，且该修改已同步到数据库。但在HTML表单中添加新金额时出现错误，而通过admin面板操作却能成功。请问如何让HTML表单接受小数？是否遗漏了某些步骤？

相关代码 #

models.py

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

class Expense(models.Model):
    amount = models.DecimalField(decimal_places=2, max_digits=10)
    date = models.DateField(default=now)
    description = models.TextField()
    owner = models.ForeignKey(to=User, on_delete=models.CASCADE)
    category = models.CharField(max_length=255)

    def __str__(self):
        return self.category

    class Meta:
        ordering = ['-date']

class Category(models.Model):
    name = models.CharField(max_length=255)

    class Meta:
        verbose_name_plural = 'Categories'

    def __str__(self):
        return self.name

views.py

@login_required(login_url="/authentication/login")
def add_expenses(request):
    categories = Category.objects.all()
    context = {
        'categories': categories,
        'values': request.POST
    }
    if request.method == 'POST':
        amount = request.POST['amount']
        description = request.POST['description']
        date = request.POST['expense_date']
        category = request.POST['category']

        Expense.objects.create(owner=request.user, amount=amount, date=date, category=category, description=description)
        messages.success(request, 'Expense saved successfully')
        return redirect('expenses')
    else:    
        return render(request, 'expenses/add-expenses.html', context)

HTML表单

<form action="{% url 'add-expenses' %}" method="post">
    {% include 'partials/messages.html' %}
    {% csrf_token %}
    <div class="form-group mb-3">
        <label for="">Categories</label>
        <select class="form-control form-control" name="category" required>
            {% for category in categories%}
            <option name="category" value="{{category.name}}">
                {{category.name}}
            </option>
            {% endfor %}
        </select>
    </div>
    <div class="form-group mb-3">
        <label for="">Amount</label>
        <input type="number" class="form-control form-control-sm" name="amount" required />
    </div>
    <div class="form-group mb-3">
        <label for="">Description</label>
        <input type="text" class="form-control form-control-sm" name="description" value="{{values.description}}">
    </div>
    <div class="form-group mb-3">
        <label for="">Date</label>
        <div class="d-grid gap-2 col-3">
            <input type="date" class="form-control form-control-sm" name="expense_date" required>
        </div>
    </div>
    <div class="d-grid gap-2 col-3">
        <input type="submit" value="Add" class="btn btn-outline-dark" />
    </div>
</form>

问题出在HTML输入控件配置和视图层类型转换两个环节，Admin面板能正常工作是因为它自动处理了DecimalField的表单校验与类型转换逻辑。

1. 修改HTML输入控件，允许小数输入 #

默认的type="number"输入框在部分浏览器中仅支持整数，需添加step="0.01"属性（对应模型中decimal_places=2的配置），明确支持两位小数输入，同时让浏览器做基础格式校验。

修改后的金额输入框代码：

<input type="number" class="form-control form-control-sm" name="amount" step="0.01" required />

2. 视图层显式转换金额为Decimal类型 #

从request.POST获取的amount是字符串类型，直接传给DecimalField可能触发类型转换错误（尤其当地区语言使用逗号作为小数分隔符时），需显式用decimal.Decimal()转换，同时添加异常处理避免格式错误导致崩溃。

修改后的views.py代码：

from decimal import Decimal  # 导入Decimal类
from django.contrib import messages

@login_required(login_url="/authentication/login")
def add_expenses(request):
    categories = Category.objects.all()
    context = {
        'categories': categories,
        'values': request.POST
    }
    if request.method == 'POST':
        try:
            # 将字符串金额转换为Decimal类型
            amount = Decimal(request.POST['amount'])
            description = request.POST['description']
            date = request.POST['expense_date']
            category = request.POST['category']

            Expense.objects.create(owner=request.user, amount=amount, date=date, category=category, description=description)
            messages.success(request, 'Expense saved successfully')
            return redirect('expenses')
        except ValueError:
            # 捕获格式错误，返回提示
            messages.error(request, '请输入有效的金额格式（例如：10.50）')
            return render(request, 'expenses/add-expenses.html', context)
    else:    
        return render(request, 'expenses/add-expenses.html', context)

3. 可选：使用Django ModelForm（更规范的方案） #

如果想彻底避免表单与模型字段不匹配的问题，推荐使用Django的ModelForm，它会自动根据模型字段生成对应表单控件，处理类型转换和校验逻辑。

步骤1：创建forms.py

from django import forms
from .models import Expense

class ExpenseForm(forms.ModelForm):
    class Meta:
        model = Expense
        fields = ['amount', 'date', 'description', 'category']
        widgets = {
            'date': forms.DateInput(attrs={'type': 'date'}),
            'amount': forms.NumberInput(attrs={'step': '0.01'}),
        }

步骤2：修改views.py

from .forms import ExpenseForm

@login_required(login_url="/authentication/login")
def add_expenses(request):
    categories = Category.objects.all()
    if request.method == 'POST':
        form = ExpenseForm(request.POST)
        if form.is_valid():
            expense = form.save(commit=False)
            expense.owner = request.user
            expense.save()
            messages.success(request, 'Expense saved successfully')
            return redirect('expenses')
        else:
            context = {'categories': categories, 'form': form}
            return render(request, 'expenses/add-expenses.html', context)
    else:
        form = ExpenseForm()
        context = {'categories': categories, 'form': form}
        return render(request, 'expenses/add-expenses.html', context)

步骤3：简化HTML表单

<form action="{% url 'add-expenses' %}" method="post">
    {% include 'partials/messages.html' %}
    {% csrf_token %}
    {{ form.as_p }}
    <div class="d-grid gap-2 col-3">
        <input type="submit" value="Add" class="btn btn-outline-dark" />
    </div>
</form>

内容的提问来源于stack exchange，提问作者adithya