djangoで掲示板作成時、特定のテーマに対するコメントを表示させたいのだが、エラーが出てしまいます。

[02/Aug/2022 15:28:56] "GET /boards/post_comments/10 HTTP/1.1" 500 85551
<WSGIRequest: GET '/boards/post_comments/10'>
Internal Server Error: /boards/post_comments/10
Traceback (most recent call last):
  File "C:\Users\aruka\anaconda3\envs\djangoenv\lib\site-packages\django\core\handlers\exception.py", line 47, in inner
    response = get_response(request)
  File "C:\Users\aruka\anaconda3\envs\djangoenv\lib\site-packages\django\core\handlers\base.py", line 181, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "C:\Users\aruka\anaconda3\envs\djangoenv\lib\site-packages\django\views\generic\base.py", line 69, in view
    return self.dispatch(request, *args, **kwargs)
  File "C:\Users\aruka\anaconda3\envs\djangoenv\lib\site-packages\django\views\generic\base.py", line 101, in dispatch
    return handler(request, *args, **kwargs)
  File "C:\Users\aruka\anaconda3\envs\djangoenv\lib\site-packages\django\views\generic\edit.py", line 170, in get
    return super().get(request, *args, **kwargs)
  File "C:\Users\aruka\anaconda3\envs\djangoenv\lib\site-packages\django\views\generic\edit.py", line 135, in get
    return self.render_to_response(self.get_context_data())
  File "C:\Users\aruka\OneDrive\デスクトップ\django_exam\FunctionExam\function_project\boards\views.py", line 51, in get_context_data
    context['comments'] = Comments.objects.filter(theme_id=self.pk).order_by('id').all()
AttributeError: 'PostCommentsView' object has no attribute 'pk'
[02/Aug/2022 15:32:24] "GET /boards/post_comments/10 HTTP/1.1" 500 85551

from django.shortcuts import render, get_object_or_404
from django.urls import reverse_lazy
from django.views.generic.list import ListView
from django.views.generic.edit import CreateView, UpdateView, DeleteView
from .models import Themes, Comments
from .forms import CreateThemeForm, PostCommentsForm
from django.http import Http404
from django.contrib.auth.mixins import LoginRequiredMixin
import os

class CreateThemeView(LoginRequiredMixin, CreateView):
    template_name = os.path.join('boards', 'create_theme.html')
    form_class = CreateThemeForm
    model = Themes

    def form_valid(self, form):
        form.instance.user = self.request.user
        form.save()
        return super().form_valid(form)

class ListThemeView(ListView):
    model = Themes
    template_name = os.path.join('boards', 'list_themes.html')

class UpdateThemeView(LoginRequiredMixin, UpdateView):
    model = Themes
    template_name = os.path.join('boards', 'edit_theme.html')
    form_class = CreateThemeForm

class DeleteThemeView(LoginRequiredMixin, DeleteView):
    model = Themes
    template_name = os.path.join('boards', 'delete_theme.html')
    success_url = reverse_lazy('boards:list_themes')

class PostCommentsView(CreateView):
    model = Comments
    template_name = os.path.join('boards', 'post_comments.html')
    form_class = PostCommentsForm

    def get_success_url(self):
        return reverse_lazy('boards:post_comments', kwargs={'pk': self.object.id })

    def form_valid(self, form):
        form.instance.theme = Themes.objects.get(user_id=self.request.user.id)
        form.instance.user = self.request.user
        return super().form_valid(form)

    def get_context_data(self, **kwargs):
        context = super().get_context_data(**kwargs)
        print(self.request)
        context['comments'] = Comments.objects.filter(theme_id=self.pk).order_by('id').all()
        return context