我的 sqlalchemy 中有 2 個表
書桌
class Book(Base):
__tablename__ = 'books'
rowid = Column(Integer(), primary_key = True)
name = Column(String(50), index = True)
author = Column(String(50))
year = Column(Integer())
book_type = Column(Integer(), nullable = False)
isloaned = Column(Boolean(), nullable = False, default = False)
和貸款表
class Loans(db.Base):
__tablename__ = 'loans'
loan_id = Column(Integer(), primary_key = True)
custID = Column(Integer(), ForeignKey(customers.Customer.rowid))
bookID = Column(Integer(), ForeignKey(books.Book.rowid))
loan_date = Column(DateTime())
return_date = Column(DateTime())
islate = Column(Boolean(), default = True, nullable = False)
customername = relationship("Customer", foreign_keys = custID)
bookname = relationship("Book", foreign_keys = bookID)
貸款表通過外鍵連接到書表。
現在我有一些代碼，所以當我將一本書還給圖書館時，它會更新貸款歸還日期。
有了它，我想更新書中的孤立列，我嘗試了以下代碼：
def returnloan(loanid, date):
with mydb.session as session:
session.query(Loans).filter(Loans.loan_id == loanid).update({"return_date": date})
session.query(Loans).filter(Loans.loan_id == loanid).update({"bookname.isloaned": False})
session.commit()
但我得到一個錯誤
sqlalchemy.exc.InvalidRequestError: Invalid expression type: 'bookname.isloaned'
回傳日期已更新，但我無法訪問該書。通過外鍵借閱
有什么建議么？
uj5u.com熱心網友回復：
你只需要更新Book. 理想情況下，您還需要在 table 上使用 backref，Loans以便您可以從以下位置訪問它Book：
bookname = relationship("Book", foreign_keys=bookID, backref="loans")
使用 SQLAlchemy 1.4 語法，您將更新如下內容：
stmt = update(Loans).where(Loans.loan_id == loan_id).values(return_date=date)
session.execute(stmt)
stmt = update(Book).where(Book.loans.has(Loans.load_id == loan_id)).values(isloaned=False)
session.execute(stmt)
我認為使用您當前的語法，這可能有效：
session.query(Book).filter(Book.loans.has(Loans.load_id == loan_id)).update({"isloaned": False})
或者，這將是僅使用 ORM 的超級簡單方法：
loan = session.execute(select(Loans).where(Loans.loan_id == loan_id)).scalar()
loan.return_date = date
loan.book.isloaned = False
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標籤：Python 烧瓶 sqlalchemy