title: Topic.entry_set Issue [Django]
body: <p>I tried the fix from here but it still won't work.
  <a href="https://stackoverflow.com/questions/51909428/reversemanytoonedescriptor-object-has-no-attribute-order-by-django-2-1/62083658#62083658">ReverseManyToOneDescriptor object has no attribute order_by django 2.1</a></p>
  
  <p>What am I missing? 
  entering <a href="http://localhost:8000/topics/1/" rel="nofollow noreferrer">http://localhost:8000/topics/1/</a> gives me</p>
  
  <pre><code>Environment:
  
  
  Request Method: GET
  Request URL: http://127.0.0.1:8000/topics/1/
  
  Django Version: 3.0.6
  Python Version: 3.7.2
  Installed Applications:
  ('django.contrib.admin',
   'django.contrib.auth',
   'django.contrib.contenttypes',
   'django.contrib.sessions',
   'django.contrib.messages',
   'django.contrib.staticfiles',
   'learning_logs')
  Installed Middleware:
  ['django.middleware.security.SecurityMiddleware',
   'django.contrib.sessions.middleware.SessionMiddleware',
   'django.middleware.common.CommonMiddleware',
   'django.middleware.csrf.CsrfViewMiddleware',
   'django.contrib.auth.middleware.AuthenticationMiddleware',
   'django.contrib.messages.middleware.MessageMiddleware',
   'django.middleware.clickjacking.XFrameOptionsMiddleware']
  
  
  
  Traceback (most recent call last):
    File "E:\Personal projects\python\learning_log\venv\lib\site-packages\django\core\handlers\exception.py", line 34, in inner
      response = get_response(request)
    File "E:\Personal projects\python\learning_log\venv\lib\site-packages\django\core\handlers\base.py", line 115, in _get_response
      response = self.process_exception_by_middleware(e, request)
    File "E:\Personal projects\python\learning_log\venv\lib\site-packages\django\core\handlers\base.py", line 113, in _get_response
      response = wrapped_callback(request, *callback_args, **callback_kwargs)
    File "E:\Personal projects\python\learning_log\learning_logs\views.py", line 20, in topic
      entries = topic.entry_set.order_by('-date_added')  # lowercase "t"
  
  Exception Type: AttributeError at /topics/1/
  Exception Value: 'Topic' object has no attribute 'entry_set'
  </code></pre>
  
  <p>This is my views.py</p>
  
  <pre><code>from django.shortcuts import render
  from .models import Topic
  
  
  def index(request):
      """The home page for learning log"""
      return render(request, 'learning_logs/index.html')
  
  
  def topics(request):
      """Show all topics."""
      topics = Topic.objects.order_by('date_added')
      context = {'topics': topics}
      return render(request, 'learning_logs/topics.html', context)
  
  
  def topic(request, topic_id):
      """Show a single topic and all its entries"""
      topic = Topic.objects.get(id=topic_id)
      entries = topic.entry_set.order_by('-date_added')  # lowercase "t"
      context = {'topic': topic, 'entries': entries}
      return render(request, 'learning_logs/topic.html', context)
  </code></pre>
  
  <p>Where is the issue? how can I use entry_set?</p>
  
  <p>Thanks.</p>