python - 使用一对一和外键字段创建新模型实例

Question

型号:

class BurrowedBook(models.Model):
    # Fields
    borrow_date = models.DateField()
    return_date = models.DateField()
    actual_return_date = models.DateField(null=True)

    # Relationship Fields
    book_copy = models.OneToOneField(BookCopy)
    burrowed_by = models.ForeignKey(Member)

保存新实例:

member = Member.objects.filter(member_id=memberId)
book_copy = BookCopy.objects.filter(book=book, copy_number=book_copy_id)

BurrowedBook.objects.create(borrow_date=borrow_date, 
                              return_date=return_date, 
                              book_copy=book_copy, burrowed_by=member)

如何保存此模型的新实例？我在处理一对一字段和外键字段时遇到问题。

我收到这个错误:

Cannot assign "<QuerySet []>": "BurrowedBook.book_copy" must be a 
"BookCopy" instance.

Answer 1

出现错误是因为您试图分配一个查询集 Cannot assign "<QuerySet []>"要解决您的问题，您必须使用 get，它返回单个对象而不是查询集

member = Member.objects.get(member_id=memberId)
book_copy = BookCopy.objects.get(book=book, copy_number=book_copy_id)

另一种选择是从查询集中获取第一个对象:

book_copy = BookCopy.objects.filter(book=book, copy_number=book_copy_id)[0]