Challenge 2: Add an Inline — Possible Solution
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# catalog/admin.py

from django.contrib import admin
from .models import Author, Book, Publisher

class BookInline(admin.TabularInline):
    model = Book
    extra = 1

@admin.register(Author)
class AuthorAdmin(admin.ModelAdmin):
    list_display = ["name"]
    inlines = [BookInline]

@admin.register(Publisher)
class PublisherAdmin(admin.ModelAdmin):
    list_display = ["name"]
    inlines = [BookInline]

WHY THIS WORKS
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- BookInline is defined once and reused for BOTH AuthorAdmin and
  PublisherAdmin — an inline just needs to know which model to edit
  (Book) and how many empty "add new" rows to show (extra = 1); Django
  figures out which foreign key on Book to use for each parent based on
  which admin page it's attached to (Book.author for AuthorAdmin,
  Book.publisher for PublisherAdmin).
- Because Book has TWO ForeignKeys (author and publisher, from Chapter 6's
  challenge), this same BookInline class works correctly on both parent
  admin pages without needing a separate inline class per relationship —
  Django resolves which FK to use from the inline's context automatically
  as long as there's only one ForeignKey from Book to whichever model the
  inline is attached to.
- Editing a publisher's books directly from the publisher's own admin
  page (rather than navigating to the separate Book list and filtering)
  is exactly the convenience TabularInline exists for — related data
  that's naturally viewed and edited together, in one place.