SQLAlchemy 引发具有多对一关系的 NoForeignKeyError

Question

我有三个不同的类我想使用 SQLAlchemy 与我的数据库集成。我的关系就像 Class2 object are main 类，每个 Class2 可以有多个 Class1 对象，Class1 应该与 Class2。每个 Class3 与类型 Class1.

的两个不同类有两个一对一关系

import sqlalchemy as db
from sqlalchemy import Column, Integer, String
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import relationship
from sqlalchemy.orm import sessionmaker

Base = declarative_base()


class Class1(Base):
    __tablename__ = 'Class1s'
    id = Column(Integer, primary_key=True)
    owner = relationship("Class2", back_populates="Class1s")

    crypto_type = Column(String)
    balance = Column(Integer, primary_key=True, default=0)



class Class2(Base):
    __tablename__ = 'Class2s'

    id = Column(Integer, primary_key=True)



class Class3(Base):
    __tablename__ = 'Class3'

    id = Column(Integer, primary_key=True)
    amount = Column(Integer)

    source = relationship("Class1")
    destination = relationship("Class1")


class Database:
    def __init__(self):
        self.engine = db.create_engine("sqlite:///database.db", echo=True)

        session = sessionmaker()
        session.configure(bind=self.engine)
        Base.metadata.create_all(self.engine)


if __name__ == '__main__':
    db = Database()
    print('Database Initialized Successfully!')

    user = Class2()

这会引发以下错误：

sqlalchemy.exc.NoForeignKeysError: Could not determine join condition between parent/child tables on relationship Class1.owner - there are no foreign keys linking these tables.  Ensure that referencing columns are associated with a ForeignKey or ForeignKeyConstraint, or specify a 'primaryjoin' expression.

Answer 1

请阅读Basic Relationship Patters

您确实需要定义类下的表是如何链接的，这是使用 ForeignKey

class Class1(Base):
    __tablename__ = 'Class1s'
    id = Column(Integer, primary_key=True)
    owner = relationship("Class2", back_populates="Class1s")

    crypto_type = Column(String)
    balance = Column(Integer, primary_key=True, default=0)



class Class2(Base):
    __tablename__ = 'Class2s'

    id = Column(Integer, primary_key=True)
    class1_id = Column(ForeignKey('Class1s.id'))  # <!-- NEW **
    # Class1s = relationship("Class2", back_populates="owner")

在您的情况下，您还需要在定义 Class3 和 Class1（我猜是 Transaction 和 TransactionLeg）之间的关系时明确说明。 有关详细信息，请参阅 Handling Multiple Join Paths。

class Class3(Base):
    __tablename__ = 'Class3'

    id = Column(Integer, primary_key=True)
    amount = Column(Integer)

    source_id = Column(ForeignKey('Class2s.id'))  # <!-- NEW **
    destination_id = Column(ForeignKey('Class2s.id'))  # <!-- NEW **

    source = relationship("Class1", foreign_keys=[source_id])  # <!-- MODIFIED **
    destination = relationship("Class1",  foreign_keys=[destination_id])  # <!-- MODIFIED **

请注意，以上内容均未经过测试，可能包含拼写错误。

SQLAlchemy 引发具有多对一关系的 NoForeignKeyError

SQLAlchemy raises NoForeignKeyError with Many to One relations

python

database

orm

sqlalchemy