无法在DetailView Django中查看内容

# models.py
from django.db import models

class Book(models.Model):
    title = models.CharField(max_length=100)
    author = models.CharField(max_length=100)
    description = models.TextField()

# views.py
from django.views.generic import DetailView
from .models import Book

class BookDetailView(DetailView):
    model = Book
    template_name = 'book_detail.html'
    context_object_name = 'book'

# urls.py
from django.urls import path
from .views import BookDetailView

urlpatterns = [
    path('book/<int:pk>/', BookDetailView.as_view(), name='book_detail'),
]

# book_detail.html
<h1>{{ book.title }}</h1>
<p>Author: {{ book.author }}</p>
<p>Description: {{ book.description }}</p>