SQLAlchemy 的外键约束错误

Question

我现在正在尝试在 SQLAlchemy 中实现一个旧课程中非常简单的示例表......

我已经做到了这一点，但是当我运行代码时......

from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String, Date, MetaData
from sqlalchemy import ForeignKey
from sqlalchemy.orm import relationship
from sqlalchemy import create_engine

Base = declarative_base()
engine = create_engine('mysql://x @ amazonaws.com:3306/db', echo=True)
class Guest(Base):
    __tablename__ = "guests"
    guest_no = Column(String(4), primary_key=True)
    g_name = Column(String(20))
    g_address = Column(String(30))
    booking = relationship("Booking", back_populates="guests")
class Hotel(Base):
    __tablename__ = "hotels"
    hotel_no = Column(String(4), primary_key=True)
    h_name = Column(String(20))
    h_address = Column(String(30))
    room = relationship("Room", back_populates="hotels")
    booking = relationship("Booking", back_populates="hotels")
class Room(Base):
    __tablename__ = "rooms"
    hotel_no = Column(String(4), ForeignKey('hotels.hotel_no'), primary_key=True)
    room_no = Column(String(4), primary_key=True)
    r_type = Column(String(1))
    r_price = Column(Integer)
    hotel = relationship("Hotel", back_populates="rooms")
    booking = relationship("Booking", back_populates="rooms")
class Booking(Base):
    __tablename__ = "bookings"
    hotel_no = Column(String(4), ForeignKey('hotels.hotel_no'),  primary_key=True)
    guest_no = Column(String(4), ForeignKey('guests.guest_no'), primary_key=True)
    date_form = Column(Date, primary_key=True)
    date_to = Column(Date)
    room_no = Column(String(4), ForeignKey('rooms.room_no'), primary_key=True)
    hotel = relationship("Hotel", back_populates="bookings")
    guest = relationship("Guest", back_populates="bookings")
    room = relationship("Room", back_populates="bookings")

Base.metadata.create_all(engine)

它给了我关于 room_no 外键的错误...

2017-09-11 16:16:03 2b8010c29700 Error in foreign key constraint of table db/bookings:
FOREIGN KEY(room_no) REFERENCES rooms (room_no)
):
Cannot find an index in the referenced table where the
referenced columns appear as the first columns, or column types
in the table and the referenced table do not match for constraint.
Note that the internal storage type of ENUM and SET changed in
tables created with >= InnoDB-4.1.12, and such columns in old tables
cannot be referenced by such columns in new tables.
See http://dev.mysql.com/doc/refman/5.6/en/innodb-foreign-key-constraints.html
for correct foreign key definition.

我环顾四周，确定它们都是同一类型（它们是）并且都是主键（它们以前不是），但错误仍然存​​在。

有人知道是什么原因造成的吗？

Answer 1

因为房间有一个复合主键：(hotel_no, room_no) 您需要在预订表的外键关系中指定两列：

__table_args__ = (
        ForeignKeyConstraint(
            ['hotel_no', 'room_no'],
            ['rooms.hotel_no', 'rooms.room_no']
        ),
)