Django ORM中的左连接

from django.db.models import Q

# 获取所有作者及其对应的书籍（左连接）
authors_with_books = Author.objects.annotate(
    book_count=Count('book'),
    book_details=Subquery(
        Book.objects.filter(author=OuterRef('pk')).values('title', 'publication_date')[:1]
    )
)

from django.db.models import Q, Count, Subquery, OuterRef

# 复杂的左连接查询示例
complex_query = Author.objects.annotate(
    book_count=Count('book'),
    book_details=Subquery(
        Book.objects.filter(author=OuterRef('pk')).values('title', 'publication_date')[:1]
    )
).filter(Q(book_count__gt=0) | Q(book_details__isnull=False))

# 分页查询示例
from django.core.paginator import Paginator

authors_with_books = Author.objects.annotate(
    book_count=Count('book'),
    book_details=Subquery(
        Book.objects.filter(author=OuterRef('pk')).values('title', 'publication_date')[:1]
    )
)

paginator = Paginator(authors_with_books, 10)  # 每页10条记录
page_number = 1
page_obj = paginator.get_page(page_number)