映射器映射类无法为映射表组装任何主键列

Question

sqlalchemy.exc.ArgumentError: Mapper mapped class PartCar->partcar could not assemble any primary key columns for mapped table 'partcar'

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

Base = declarative_base()


class User(Base):
    __tablename__ = 'USER'

    user_id = Column(Integer)
    passport_number = Column(String(8), primary_key=True, nullable=False)
    user_email = Column(String(20), nullable=False)
    user_name = Column(String(20), nullable=False)

    carHave = relationship('Car', secondary='caruser')


class Car(Base):
    __tablename__ = 'car'

    car_number = Column(Integer, primary_key=True, nullable=False)

    userHave = relationship('User', secondary='caruser')
    partHave = relationship('Part', secondary='partcar')


class Part(Base):
    __tablename__ = 'part'

    part_name = Column(String(20), primary_key=True, nullable=False)

    carHave = relationship('Car', secondary='partcar')


class CarUser(Base):
    __tablename__ = 'caruser'

    user_passport_number = Column(String(8), ForeignKey('USER.passport_number'))
    car_number = Column(Integer, ForeignKey('car.car_number'))
    car_model = Column(String(20), nullable=False)


class PartCar(Base):
    __tablename__ = 'partcar'

    part_car_number = Column(Integer, ForeignKey('car.car_number'))
    part_name = Column(String(20), ForeignKey('part.part_name'))
    part_price = Column(Integer, nullable=False)

Answer 1

你PartCar表，没有一个主键，为此，SQLAlchemy的是引发错误。

Flask-SQLAlchemy 需要一个主键，因为SQLAlchemy ORM 需要一个主键：

SQLAlchemy ORM，为了映射到特定的表，需要至少有一个列表示为主键列。

大多数 ORM 要求对象定义某种主键，因为内存中的对象必须对应于数据库表中唯一可识别的行。