如何限制在ForeignKey/ManyToMany Wagtail ModelAdmin字段中显示的项？

from django.db import models
from wagtail.contrib.modeladmin.options import ModelAdmin, modeladmin_register
from myapp.models import Book

class BookAdmin(ModelAdmin):
    model = Book
    menu_label = 'Books'
    menu_icon = 'book'
    menu_order = 200
    add_to_settings_menu = False
    exclude_from_explorer = False
    list_display = ('title', 'author')

    def get_queryset(self, request):
        qs = super().get_queryset(request)
        # 限制 author 字段中只显示姓氏为 "Smith" 的作者
        qs = qs.filter(author__last_name='Smith')
        return qs

modeladmin_register(BookAdmin)

from django.db import models
from wagtail.contrib.modeladmin.options import ModelAdmin, modeladmin_register
from myapp.models import Book

class BookAdmin(ModelAdmin):
    model = Book
    menu_label = 'Books'
    menu_icon = 'book'
    menu_order = 200
    add_to_settings_menu = False
    exclude_from_explorer = False
    list_display = ('title', 'authors')

    def formfield_for_manytomany(self, db_field, request, **kwargs):
        if db_field.name == 'authors':
            # 限制 authors 字段中只显示姓氏为 "Smith" 的作者
            kwargs['queryset'] = db_field.remote_field.model.objects.filter(last_name='Smith')
        return super().formfield_for_manytomany(db_field, request, **kwargs)

modeladmin_register(BookAdmin)