django 最后一个标记对象不可订阅

Question

我很抱歉问但是...

我一直在尝试使用我的 Django 框架在我的 HTML 中使用这个 "last" 标签，以便在我的 html 上显示我数据库中的最后一个对象；这里文档：https://docs.djangoproject.com/en/2.1/ref/templates/builtins/

现在的问题是当我在我的代码中使用我的 "last" 标签时；

<div class = "float-right  my-4 chartjs-render-monitor" id="chartContainerPH" style="width: 49%; height: 400px;display: inline-block; background-color:#FDFDFD;">
<center>
    <a class="title-link" href="{%url 'ph' %}">PH:</a>
    <p> {% for tank_system in tank %}{{tank_system.PH|last}}, {%endfor%}</p>
    </center>

</div>

并得到这个错误；

TypeError at /
'decimal.Decimal' object is not subscriptable
Request Method: GET
Request URL:    http://127.0.0.1:8000/
Django Version: 2.1.3
Exception Type: TypeError
Exception Value:    
'decimal.Decimal' object is not subscriptable
Exception Location: C:\Users\user\AppData\Local\Programs\Python\Python37-32\lib\site-packages\django\template\defaultfilters.py in last, line 540
Python Executable:  C:\Users\user\AppData\Local\Programs\Python\Python37-32\python.exe
Python Version: 3.7.1
Python Path:    
['C:\Users\user\Desktop\FrounterWeb- postgreDB',
 'C:\Users\user\AppData\Local\Programs\Python\Python37-32\python37.zip',
 'C:\Users\user\AppData\Local\Programs\Python\Python37-32\DLLs',
 'C:\Users\user\AppData\Local\Programs\Python\Python37-32\lib',
 'C:\Users\user\AppData\Local\Programs\Python\Python37-32',
 'C:\Users\user\AppData\Local\Programs\Python\Python37-32\lib\site-packages']
Server time:    Thu, 6 Dec 2018 11:12:47 +0800

我不清楚这个错误，但即使在阅读这里之后： In Python, what does it mean if an object is subscriptable or not?

这是我的模型代码；

from django.db import models
from django.utils import timezone
# having errors KeyError: "'__name__' not in globals"

class tank_system(models.Model):
    PH = models.DecimalField(max_digits=3, decimal_places=1)
    EC = models.DecimalField(max_digits=3, decimal_places=1)
    WaterLevel = models.IntegerField(default=100)
    TempWater = models.IntegerField(default=0)
    TempRoom = models.IntegerField(default=0)
    datetime = models.DateTimeField(default=timezone.now())



    def get_last(self):
        try:
            print(self)
            return self.set.all().order_by('-date')[0]
        except IndexError:
            pass

这里是我的视图代码；

from django.shortcuts import render
from django.views.generic import TemplateView
from zigview.models import tank_system

from django.contrib.auth.decorators import login_required
import logging
logger = logging.getLogger(__name__)
from django.core.mail import send_mail



try:
    @login_required(login_url='/accounts/login/')
    def index(request): #gose to main dashboard page
        #tank = tank_system.objects.all()
        tank = tank_system.objects.extra(select={'is_recent':"datetime>'2006-01-01'"})
        return render(request,'FrounterWeb/extends/includes.html',{'tank':tank})
except:
    logger.error('index page request failed/errors')

不好意思问

Answer 1

您可以测试 for 循环是否引用了带有 forloop.last 的最后一项，然后查找 PH 属性：

<center>
    <a class="title-link" href="{%url 'ph' %}">PH:</a>
    <p> 
       {% for tank_system in tank %}
           {% if forloop.last %}
               {{ tank_system.PH }}, 
           {% endif %}
       {% endfor %}
    </p>
</center>

似乎尝试在 tanks 的查询集上使用 Django 的 last 模板标记会给出 "Negative indexing is not supported" 错误。

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