조회수 기능을 구현하였는데 이해가 안가는 부분이 있어서 질문글을 올립니다..
보시면

models.py

from django.db import models
from django.db.models import Count
from django.urls import reverse
from django.contrib.auth.models import User


class Category(models.Model):
    name = models.CharField(max_length=20, unique=True)
    description = models.CharField(max_length=200, null=True, blank=True)
    has_answer = models.BooleanField(default=True)  # 답변가능 여부

    def __str__(self):
    #     return self.name
        return self.description

    def get_absolute_url(self):
        return reverse('pybo:index', args=[self.name])


class Question(models.Model):
    author = models.ForeignKey(User, on_delete=models.CASCADE, related_name='author_question')
    subject = models.CharField(max_length=200)
    content = models.TextField()
    create_date = models.DateTimeField()
    modify_date = models.DateTimeField(null=True, blank=True)
    voter = models.ManyToManyField(User, related_name='voter_question')  # 추천인 추가
    category = models.ForeignKey(Category, on_delete=models.CASCADE, related_name='category_question')
    seen_cnt = models.PositiveIntegerField(default=0)

    def __str__(self):
        return self.subject

    @staticmethod
    def order_by_so(question_list, so):
        if so == 'recommend':
            # aggretation, annotation에는 relationship에 대한 역방향 참조도 가능 (ex. Count('voter'))
            question_list = question_list.annotate(num_voter=Count('voter')).order_by('-num_voter', '-create_date')
        elif so == 'popular':
            question_list = question_list.annotate(num_answer=Count('answer')).order_by('-num_answer', '-create_date')
        else:  # so == 'recent':
            question_list = question_list.order_by('-create_date')

        return question_list

    def get_absolute_url(self):
        return reverse('pybo:detail', args=[self.id])
    # 조회수 기능 추가 
    @property
    def update_counter(self):
        self.seen_cnt = self.seen_cnt+1
        self.save()


class Answer(models.Model):
    author = models.ForeignKey(User, on_delete=models.CASCADE, related_name='author_answer')
    question = models.ForeignKey(Question, on_delete=models.CASCADE)
    content = models.TextField()
    create_date = models.DateTimeField()
    modify_date = models.DateTimeField(null=True, blank=True)
    voter = models.ManyToManyField(User, related_name='voter_answer')  # 추천인 추가

    def __str__(self):
        return self.content

    @staticmethod
    def order_by_so(answer_list, so):
        # 정렬
        if so == 'recommend':

            answer_list = answer_list.annotate(num_voter=Count('voter')).order_by('-num_voter', '-create_date')
        else:  # so == 'recent':
            answer_list = answer_list.order_by('-create_date')

        return answer_list

    def get_page(self, so='recommend'):
        # https://stackoverflow.com/questions/1042596/get-the-index-of-an-element-in-a-queryset
        answer_list = Answer.order_by_so(self.question.answer_set.all(), so)

        index = 0
        for _answer in answer_list:
            index += 1
            if self == _answer:
                break

        return (index - 1)//5 + 1

    # def get_relative_url(self, so, page):
    #     return reverse('pybo:detail', args=[self.question.id]) + f'?page={page}&so={so}#answer_{self.id}'

    def get_absolute_url(self):
        return reverse('pybo:detail', args=[self.question.id]) + f'?page={self.get_page()}#answer_{self.id}'


class Comment(models.Model):
    author = models.ForeignKey(User, on_delete=models.CASCADE, related_name='author_comment')
    content = models.TextField()
    create_date = models.DateTimeField()
    modify_date = models.DateTimeField(null=True, blank=True)
    question = models.ForeignKey(Question, null=True, blank=True, on_delete=models.CASCADE)
    answer = models.ForeignKey(Answer, null=True, blank=True, on_delete=models.CASCADE)

    def __str__(self):
        return self.content

    def get_absolute_url(self):
        if self.question:
            return reverse('pybo:detail', args=[self.question.id]) + '#comment_question_start'
        else:  # if self.answer:
            return reverse('pybo:detail', args=[self.answer.question.id]) + \
                   f'?page={self.answer.get_page()}#comment_{self.id}'  # todo comment_id 가능?

models.py에서 Question 클래스에

seen_cnt = models.PositiveIntegerField(default=0)

    # 조회수 기능 추가 
    @property
    def update_counter(self):
        self.seen_cnt = self.seen_cnt+1
        self.save()

을 추가하였는데
이렇다면 question_list.html에서 단순히 조회수를 조회하는 부분엔

{{ question.seen_cnt }}

를 사용하고 ,
게시글의 상세페이지를 클릭해서 들어갈땐 ( question_detail.html )

{{ question.update_counter }}

를 사용해야하는 것 아닌가요? 왜 이렇게하면 None이 출력되고

question_list.html와 question_detail.html 두곳에서 모두 {{ question.seen_cnt }}를 사용해야 정상동작하는지 이유를 모르겠습니다..

사용한 템플릿 : question_list.html

{% extends 'base.html' %}
{% load pybo_filter %}

{% block content %}
<nav id="sidebar" class="border-top border-secondary">
    <div class="list-group text-lg-start-center">
        {% for cat in category_list %}
            {% if cat == category %}
                <a class="rounded-0 list-group-item list-group-item-action list-group-item-light active"
                   href="{{ cat.get_absolute_url }}">{{ cat.description }}</a>
            {% else %}
                <a class="rounded-0 list-group-item list-group-item-action list-group-item-light"
                   href="{{ cat.get_absolute_url }}">{{ cat.description }}</a>
            {% endif %}
        {% endfor %}
    </div>
</nav>

<div class="row justify-content-between my-3">
    <div class="col-2">
        <select class="form-control so">
            <option value="recent" {% if so == 'recent' %}selected{% endif %}>최신순</option>
            <option value="recommend" {% if so == 'recommend' %}selected{% endif %}>추천순</option>
            <option value="popular" {% if so == 'popular' %}selected{% endif %}>답변순</option>
        </select>
    </div>
    <div class="col-6">
        <div class="input-group">
            <input type="text" id ="search_kw" class="form-control" value="{{ kw|default_if_none:'' }}">
            <div class="input-group-append">
                <button class="btn btn-outline-secondary" type="button" id="btn_search">찾기</button>
            </div>
        </div>
    </div>
</div>

<table class="table">
    <thead>
        <tr class="text-center thead-dark">
            <th>번호</th>
            <th>추천</th>
            <th style="width:50%">제목</th>
            <th>글쓴이</th>
            <th>조회</th>
            <th>작성일시</th>
        </tr>
    </thead>
    <tbody>
    {% if question_list %}
    {% for question in question_list %}
    <tr class="text-center">
        <td>
            <!-- 번호 = 전체건수 - 시작인덱스 - 현재인덱스 + 1 -->
            {{ question_list.paginator.count|sub:question_list.start_index|sub:forloop.counter0|add:1 }}
        </td>
        <td>
            {% if question.voter.all.count > 0 %}
                <span class="text-danger small mx-2">{{ question.voter.count }}</span>
                    <!-- question.voter.count와 완전히 같은 쿼리(SQL문 동일) -->
            {% else %}
                <span class="badge badge-light px-2 py-1" style="color:#ccc;">0</span>
            {% endif %}
        </td>
        <td class="text-left">
            <a href="{{ question.get_absolute_url }}">{{ question.subject }}</a>
            {% if question.answer_set.count > 0 %}
            <span class="text-danger small ml-2">{{ question.answer_set.count }}</span>
            {% endif %}
        </td>
        <td>
            <a href="{% url 'common:profile_base' question.author.id %}">{{ question.author.username }}</a>
        </td>
        <!-- 조회수 -->
        <td>{{ question.seen_cnt }}</td>
        <!--작성일-->
        <td>{{ question.create_date }}</td>
    </tr>
    {% endfor %}
    {% else %}
    <tr>
        <td colspan="3">질문이 없습니다.</td>
    </tr>
    {% endif %}
    </tbody>
</table>
<!-- 페이징처리 시작 -->
<ul class="pagination justify-content-center">
    <!-- 이전페이지 -->
    {% if question_list.has_previous %}
        <li class="page-item">
            <a class="page-link"  href="?page=1">처음</a>
        </li>
       <li class="page-item">
            <a class="page-link" href="?page={{ question_list.previous_page_number }}">이전</a>
        </li>
    {% else %}
        <li class="page-item disabled">
            <a class="page-link" tabindex="-1" aria-disabled="true" href="#">처음</a>
        </li>
        <li class="page-item disabled">
            <a class="page-link" tabindex="-1" aria-disabled="true" href="#">이전</a>
        </li>
    {% endif %}
    <!-- 페이지리스트 -->
    {% for page_number in question_list.paginator.page_range %}
        {% if page_number >= question_list.number|add:-4 and page_number <= question_list.number|add:4 %}
            {% if page_number == question_list.number %}
            <li class="page-item active" aria-current="page">
                <a class="page-link"  href="?page={{ page_number }}">{{ page_number }}</a>
            </li>
            {% else %}
            <li class="page-item">
                <a class="page-link"  href="?page={{ page_number }}">{{ page_number }}</a>
            </li>
            {% endif %}
        {% endif %}
    {% endfor %}
    <!-- 다음페이지 -->
    {% if question_list.has_next %}
        <li class="page-item">
             <a class="page-link" href="?page={{ question_list.next_page_number }}">다음</a>
        </li>
        <li class="page-item">
             <a class="page-link" href="?page={{ question_list.paginator.count }}">끝</a>
        </li>
    {% else %}
        <li class="page-item disabled">
            <a class="page-link" tabindex="-1" aria-disabled="true" href="#">다음</a>
        </li>
        <li class="page-item disabled">
            <a class="page-link" tabindex="-1" aria-disabled="true" href="#">끝</a>
        </li>
    {% endif %}
</ul>
<!-- 페이징처리 끝 -->
<a href="{% url 'pybo:question_create' category.name %}" class="btn btn-primary">질문 등록하기</a>

<form id="searchForm" method="get" action="{{ category.get_absolute_url }}">
    <input type="hidden" id="kw" name="kw" value="{{ kw|default_if_none:'' }}">
    <input type="hidden" id="page" name="page" value="{{ page }}">
    <input type="hidden" id="so" name="so" value="{{ so }}">
</form>
{% endblock %}

{% block script %}
<script type='text/javascript'>
const page_elements = document.getElementsByClassName("page-link");
Array.from(page_elements).forEach(function(element) {
    element.addEventListener('click', function() {
        document.getElementById('page').value = this.dataset.page;
        document.getElementById('searchForm').submit();
    });
});
const btn_search = document.getElementById("btn_search");
btn_search.addEventListener('click', function() {
    document.getElementById('kw').value = document.getElementById('search_kw').value;
    document.getElementById('page').value = 1;  // 검색버튼을 클릭할 경우 1페이지부터 조회한다.
    document.getElementById('searchForm').submit();
});
</script>

<script type='text/javascript'>
    $(document).ready(function() {
        $(".page-link").on('click', function() {
            $("#page").val($(this).data("page"));
            $("#searchForm").submit();
        });

        $("#btn_search").on('click', function() {
            $("#kw").val($(".kw").val());
            $("#page").val(1);  // 검색 버튼을 클릭할 경우 1페이지부터 조회한다.
            $("#searchForm").submit();
        });

        $(".so").on('change', function() {
            $("#so").val($(this).val());
            $("#page").val(1);  // 새로운 기준으로 정렬할 경우 1페이지부터 조회한다.
            $("#searchForm").submit();
        });
    });
</script>
{% endblock %}

사용한 템플릿 : question_detail.html

{% extends 'base.html' %}
{% block content %}
{% load pybo_filter %}

<div class="container my-3">
    <!-- message 표시 -->
    {% if messages %}
    <div class="alert alert-danger my-3" role="alert">
        {% for message in messages %}
        <strong>{{ message.tags }}</strong>
        <ul>
            <li>{{ message.message }}</li>
        </ul>
        {% endfor %}
    </div>
    {% endif %}
    <!-- 질문 -->
    <h2 class="border-bottom py-2">[{{category.description}}]{{ question.subject }}</h2>
    <!--조회수 -->
    <h3> 조회: {{ question.seen_cnt }} </h3>
    <div class="card my-3">
        <div class="card-body">
<!--            <div class="card-text" style="white-space: pre-line;">{{ question.content }}</div>-->
                <div class="card-text">{{ question.content|mark }}</div>
            <div class="d-flex justify-content-end">
                {% if question.modify_date %}
                <div class="badge bg-light text-dark p-2 text-start mx-3">
                    <div class="mb-2">modified at</div>
                    <div>{{ question.modify_date }}</div>
                </div>
                {% endif %}
                <div class="badge bg-light text-dark p-2 text-start">
                    <div class="mb-2">{{ question.author.username }}</div>
                    <div>{{ question.create_date }}</div>
                </div>
            </div>
            <div class="my-3">
                <a href="javascript:void(0)" data-uri="{% url 'pybo:vote_question' question.id %}"
                   class="recommend btn btn-sm btn-outline-secondary"> 추천
                    <span class="badge rounded-pill bg-success">{{question.voter.count}}</span>
                </a>
                {% if request.user == question.author %}
                <a href="{% url 'pybo:question_modify' question.id   %}"
                   class="btn btn-sm btn-outline-secondary">수정</a>
                <a href="javascript:void(0)" class="delete btn btn-sm btn-outline-secondary"
                   data-uri="{% url 'pybo:question_delete' question.id  %}">삭제</a>
                {% endif %}
            </div>
        </div>
    </div>
    <!-- 답변 -->
    <h5 class="border-bottom my-3 py-2">{{question.answer_set.count}}개의 답변이 있습니다.</h5>
    {% for answer in answer_list %}
    <div class="card my-3">
        <div class="card-body">
<!-- 답변내용 -->
<!--            <div class="card-text" style="white-space: pre-line;">{{ answer.content }}</div>-->
            <div class="card-text" >{{ answer.content|mark }}</div>
            <div class="d-flex justify-content-end">
                {% if answer.modify_date %}
                <div class="badge bg-light text-dark p-2 text-start mx-3">
                    <div class="mb-2">modified at</div>
                    <div>{{ answer.modify_date }}</div>
                </div>
                {% endif %}
                <div class="badge bg-light text-dark p-2 text-start">
                    <div class="mb-2">{{ answer.author.username }}</div>
                    <div>{{ answer.create_date }}</div>
                </div>
            </div>
            <div class="my-3">
                <a href="javascript:void(0)" data-uri="{% url 'pybo:vote_answer' answer.id  %}"
                   class="recommend btn btn-sm btn-outline-secondary"> 추천
                    <span class="badge rounded-pill bg-success">{{answer.voter.count}}</span>
                </a>
                {% if request.user == answer.author %}
                <a href="{% url 'pybo:answer_modify' answer.id  %}"
                   class="btn btn-sm btn-outline-secondary">수정</a>
                <a href="javascript:void(0)" class="delete btn btn-sm btn-outline-secondary "
                   data-uri="{% url 'pybo:answer_delete' answer.id  %}">삭제</a>
                {% endif %}
            </div>
        </div>
    </div>
    {% endfor %}
    <!-- 답변 페이징처리 시작 -->
    <ul class="pagination justify-content-center">
        <!--처음페이지-->
        <li class="page-item">
            <a class="page-link" href="?page=1">처음</a>

        <!-- 이전페이지 -->
        {% if answer_list.has_previous %}
        <li class="page-item">
            <a class="page-link" href="?page={{ answer_list.previous_page_number }}">이전</a>
        </li>
        {% else %}
        <li class="page-item disabled">
            <a class="page-link" tabindex="-1" aria-disabled="true"
               href="javascript:void(0)">이전</a>
        </li>
        {% endif %}
        <!-- 페이지리스트 -->
        {% for page_number in answer_list.paginator.page_range %}
        {% if page_number >= answer_list.number|add:-2 and page_number <= answer_list.number|add:2%}
        {% if page_number == answer_list.number %}
        <li class="page-item active" aria-current="page">
            <a class="page-link" href="?page={{ page_number }}">{{ page_number }}</a>
        </li>
        {% else %}
        <li class="page-item">
            <a class="page-link" href="?page={{ page_number }}">{{ page_number }}</a>
        </li>
        {% endif %}
        {% endif %}
        {% endfor %}
        <!-- 다음페이지 -->
        {% if answer_list.has_next %}
        <li class="page-item">
            <a class="page-link" href="?page={{ answer_list.paginator.num_pages }}">다음</a>
        </li>
        {% else %}
        <li class="page-item disabled">
            <a class="page-link" tabindex="-1" aria-disabled="true"
               href="javascript:void(0)">다음</a>
        </li>
        {% endif %}
        <!--마지막페이지-->
        <li class="page-item">
            <a class="page-link" href="?page={{ answer_list.paginator.count }}">끝</a>
        </li>
    </ul>
    <!-- 답변 페이징처리 끝 -->

    <form action="{% url 'pybo:answer_create' question.id %}" method="post" class="my-3">
        {% csrf_token %}
        {% include "form_errors.html" %}
        <div class="mb-3">
            <label for="content" class="form-label">답변내용</label>
            <textarea {% if not user.is_authenticated %}disabled{% endif %}
                      name="content" id="content" class="form-control" rows="10"></textarea>
        </div>
        <input type="submit" value="답변등록" class="btn btn-primary">
    </form>
</div>
{% endblock %}
{% block script %}
<script type='text/javascript'>
const delete_elements = document.getElementsByClassName("delete");
Array.from(delete_elements).forEach(function(element) {
    element.addEventListener('click', function() {
        if(confirm("정말로 삭제하시겠습니까?")) {
            location.href = this.dataset.uri;
        };
    });
});
const recommend_elements = document.getElementsByClassName("recommend");
Array.from(recommend_elements).forEach(function(element) {
    element.addEventListener('click', function() {
        if(confirm("정말로 추천하시겠습니까?")) {
            location.href = this.dataset.uri;
        };
    });
});
</script>
{% endblock %}