[英]Self-referencing many-to-many relationship with an association object in SQLAlchemy
[英]Self referencing many-to-many relationship with extra column in association object
我是 Sqlalchemy 的新手,並試圖通過relationship()
實現以下目標:
User
表。invite_code
。invitation
列表,每個invitation
都包含invite_code
和被邀請User
我認為User
和Invitation
之間的關系是一對多的。 由於Invitation
包含User
,那么我認為使用自引用關系來表示邀請者到邀請(被邀請者)關系並使用關聯invite_code
來存儲邀請碼可能會更好。
我檢查了sqlalchemy 文檔和問題,試圖實現這樣的分類:
from sqlalchemy import Column, Integer, ForeignKey, create_engine, String
from sqlalchemy.orm import relationship, sessionmaker
from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()
class Invitation(Base):
__tablename__ = 'invitation'
invite_code = Column(Integer)
inviter_id = Column(Integer, ForeignKey('user.id'), primary_key=True)
invitee_id = Column(Integer, ForeignKey('user.id'), primary_key=True)
invitee = relationship('User') #Need HELP here
class User(Base):
__tablename__ = 'user'
id = Column(Integer, primary_key=True)
name = Column(String)
inviters = relationship('User',
secondary='invitation',
primaryjoin=id==Invitation.invitee_id,
secondaryjoin=id==Invitation.inviter_id,
backref='invitees')
invitations = relationship('Invitation')# Need HELP here
def __repr__(self):
return f'User: {self.name}'
if __name__ == '__main__':
engine = create_engine('sqlite://')
Base.metadata.create_all(engine)
Session = sessionmaker(engine)
db = Session()
inviter1 = User(name='inviter1')
inviter2 = User(name='inviter2')
invitee1= User(name='invitee1')
invitee2 = User(name='invitee2')
inviter1.invitees = [invitee1, invitee2]
inviter2.invitees = [invitee1]
db.add(inviter1)
db.add(inviter2)
db.add(invitee1)
db.add(invitee2)
db.commit()
users = db.query(User).all()
for user in users:
print(user)
print(' Inviter: ', user.inviters)
print(' Invitee: ', user.invitees)
print()
如果#Need HELP here
的行被刪除,我可以得到對應的invitationer和被邀請人,但不能得到invite_code
。 如果添加#Need HELP here
代碼,則錯誤為:
Exception has occurred: AmbiguousForeignKeysError
Could not determine join condition between parent/child tables on relationship Invitation.invitee - there are multiple foreign key paths linking the tables. Specify the 'foreign_keys' argument, providing a list of those columns which should be counted as containing a foreign key reference to the parent table.
有沒有辦法在關聯 object 中添加額外的數據列,例如關聯 object 用於自引用表的多對多關系?
抱歉文字太多,在web上沒有找到任何參考文檔。
最后,我在foreign_keys
的幫助下弄清楚了:
from sqlalchemy import Column, Integer, ForeignKey, create_engine, String
from sqlalchemy.orm import relationship, sessionmaker
from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()
class User(Base):
__tablename__ = 'user'
id = Column(Integer, primary_key=True)
name = Column(String)
sent_invitations = relationship('Invitation', foreign_keys='Invitation.inviter_id', back_populates='inviter', cascade='all, delete')
received_invitations=relationship('Invitation', foreign_keys='Invitation.invitee_id', back_populates='invitee', cascade='all, delete')
def __repr__(self):
return f'User: {self.name}'
class Invitation(Base):
__tablename__ = 'invitation'
id = Column(Integer, primary_key=True)
invite_code = Column(Integer)
inviter_id = Column(Integer, ForeignKey('user.id'))
invitee_id = Column(Integer, ForeignKey('user.id'))
inviter=relationship('User', foreign_keys=[inviter_id], back_populates='sent_invitations')
invitee=relationship('User', foreign_keys=[invitee_id], back_populates='received_invitations')
def __repr__(self):
return f'Invitation: {self.inviter} invited {self.invitee} with {self.invite_code}'
if __name__ == '__main__':
engine = create_engine('sqlite://')
Base.metadata.create_all(engine)
Session = sessionmaker(engine)
db = Session()
inviter1 = User(name='inviter1')
inviter2 = User(name='inviter2')
invitee1= User(name='invitee1')
invitee2 = User(name='invitee2')
invitation1 = Invitation(invite_code=50, inviter=inviter1, invitee=invitee1)
invitation2 = Invitation(invite_code=20, inviter=inviter2, invitee=invitee2)
invitation3 = Invitation(invite_code=22, inviter=inviter1, invitee=inviter2)
invitation4 = Invitation(invite_code=44, inviter=invitee1, invitee=inviter2)
db.add(inviter1)
db.add(inviter2)
db.add(invitee1)
db.add(invitee2)
db.commit()
users = db.query(User).all()
for user in users:
print(user)
print(' sent_invitation: ', user.sent_invitations)
print(' received_invitation: ', user.received_invitations)
print()
invitations = db.query(Invitation).all()
for invitation in invitations:
print(invitation)
db.delete(inviter1)
db.delete(invitee2)
db.commit()
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