Django模板中{% with %}标签的变量作用域与累加陷阱

<tbody>
  {% with total=0 %}
  {% for inv in row.investmentdetails_set.all %}
  <tr>
    <th>{{ inv.investment_type }}</th>
    <td class="text-center">{{ inv.enterprise }}</td>
    <td class="text-center">{{ inv.investment }}</td>
    <td class="text-center">{{ inv.investment_date|date:'Y-m-d' }}</td>
    <td class="text-center">{{ inv.maturity_date|date:'Y-m-d' }}</td>
    <td class="text-center">{{ inv.monthly_returns }}</td>
    <td class="text-center">{{ inv.maturity_status }}</td>
  </tr>
  {# 尝试在内部with块中更新total #}
  {% with total=total|add:inv.monthly_returns %}{% endwith %}
  {% endfor %}
  <tr>
    <td colspan="7">总计：{{ total }}</td> {# 期望这里显示累加结果 #}
  </tr>
  {% endwith %}
</tbody>

from jinja2.nativetypes import NativeEnvironment

env = NativeEnvironment()

# 示例1: 在循环中直接使用变量，但Jinja2默认变量也是不可变的，除非使用特殊赋值
# 这里只是为了说明如果能直接修改，会如何表现
t1 = env.from_string(
    '{% for i in range(5) %}'
        '{{ total+i }}' # 每次都基于传入的total=0计算
    '{% endfor %}'
    '{{ "**" + total|string }}' # 外部total仍是0
)
print(t1.render(total=0)) # 输出: '01234**0'

# 示例2: 在Jinja2中使用with，效果与Django类似
t2 = env.from_string('{% for i in range(5) %}{% with total=total+i %}{% endwith %}{% endfor %}{{ "**" + total|string }}')
print(t2.render(total=0)) # 输出: '**0'

# views.py
from django.shortcuts import render
from .models import Row, InvestmentDetails # 假设你的模型

def investment_report(request, row_id):
    row_obj = Row.objects.get(id=row_id)
    investment_details = row_obj.investmentdetails_set.all()

    total_monthly_returns = 0
    for inv in investment_details:
        total_monthly_returns += inv.monthly_returns

    context = {
        'row': row_obj,
        'investment_details': investment_details,
        'total_monthly_returns': total_monthly_returns, # 将计算结果传递给模板
    }
    return render(request, 'your_template.html', context)

# views.py
from django.shortcuts import render
from django.db.models import Sum
from .models import Row, InvestmentDetails

def investment_report(request, row_id):
    row_obj = Row.objects.get(id=row_id)
    investment_details = row_obj.investmentdetails_set.all()

    # 使用ORM聚合函数计算总和
    aggregation_result = investment_details.aggregate(total_sum=Sum('monthly_returns'))
    total_monthly_returns = aggregation_result['total_sum'] if aggregation_result['total_sum'] is not None else 0

    context = {
        'row': row_obj,
        'investment_details': investment_details,
        'total_monthly_returns': total_monthly_returns,
    }
    return render(request, 'your_template.html', context)

<tbody>
  {% for inv in investment_details %} {# 直接迭代视图传递过来的数据 #}
  <tr>
    <th>{{ inv.investment_type }}</th>
    <td class="text-center">{{ inv.enterprise }}</td>
    <td class="text-center">{{ inv.investment }}</td>
    <td class="text-center">{{ inv.investment_date|date:'Y-m-d' }}</td>
    <td class="text-center">{{ inv.maturity_date|date:'Y-m-d' }}</td>
    <td class="text-center">{{ inv.monthly_returns }}</td>
    <td class="text-center">{{ inv.maturity_status }}</td>
  </tr>
  {% endfor %}
  <tr>
    <td colspan="7">总计：{{ total_monthly_returns }}</td> {# 直接显示视图计算好的总和 #}
  </tr>
</tbody>