如何访问/修改django模型字段，然后在Listview中验证其表单

from django.db import models

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

from django.views.generic import ListView
from .models import Book

class BookListView(ListView):
    model = Book
    template_name = 'book_list.html'

{% for book in object_list %}
    <p>Title: {{ book.title }}</p>
    <p>Author: {{ book.author }}</p>
{% endfor %}

class BookListView(ListView):
    model = Book
    template_name = 'book_list.html'

    def get(self, request, *args, **kwargs):
        title = request.GET.get('title', '')
        if not title:
            # 如果title字段为空，返回错误信息
            return HttpResponse('Title field is required.')
        return super().get(request, *args, **kwargs)