通过SqlAlchemy中的关联对象进行多对多，自引用，非对称关系（Twitter模型）

通过SqlAlchemy中的关联对象进行多对多，自引用，非对称关系（Twitter模型）

这已经在这里 几乎
得到了回答。在这里，这可以通过使用裸链接表进行 多对多
的优势而得到改善。 __

我在SQL和SqlAlchemy中都不擅长，但是由于我在较长时间内一直牢记此问题，因此我试图找到一种兼具以下优点的解决方案：具有附加属性的关联对象和诸如裸链接的
直接 关联表（它本身不提供关联对象）。通过 *** 作程序的其他建议，以下内容对我来说似乎很安静：

#!/usr/bin/env python3# coding: utf-8import sqlalchemy as sqAlfrom sqlalchemy.ext.declarative import declarative_basefrom sqlalchemy.orm import sessionmaker, relationship, backreffrom sqlalchemy.ext.associationproxy import association_proxyengine = sqAl.create_engine('sqlite:///m2m-w-a2.sqlite') #, echo=True)metadata = sqAl.schema.metaData(bind=engine)base = declarative_base(metadata)class UserProfile(base):  __tablename__ = 'user'  id = sqAl.Column(sqAl.Integer, primary_key=True)  full_name     = sqAl.Column(sqAl.Unipre(80))  gender        = sqAl.Column(sqAl.Enum('M','F','D', name='gender'), default='D', nullable=False)  description   = sqAl.Column(sqAl.Unipre(280))  following     = association_proxy('followeds', 'followee')  followed_by   = association_proxy('followers', 'follower')  def follow(self, user, **kwargs):    Follow(follower=self, followee=user, **kwargs)  def __repr__(self):    return 'UserProfile({})'.format(self.full_name)class Follow(base):  __tablename__ = 'follow'  followee_id   = sqAl.Column(sqAl.Integer, sqAl.ForeignKey('user.id'), primary_key=True)  follower_id   = sqAl.Column(sqAl.Integer, sqAl.ForeignKey('user.id'), primary_key=True)  status        = sqAl.Column(sqAl.Enum('A','B', name=u'status'), default=u'A')  created       = sqAl.Column(sqAl.DateTime, default=sqAl.func.now())  followee      = relationship(UserProfile, foreign_keys=followee_id, backref='followers')  follower      = relationship(UserProfile, foreign_keys=follower_id, backref='followeds')  def __init__(self, followee=None, follower=None, **kwargs):    """necessary for creation by append()ing to the association proxy 'following'"""    self.followee = followee    self.follower = follower    for kw,arg in kwargs.items():      setattr(self, kw, arg)base.metadata.create_all(engine, checkfirst=True)session = sessionmaker(bind=engine)()def create_sample_data(sess):  import random  usernames, fstates, genders = ['User {}'.format(n) for n in range(4)], ('A', 'B'), ('M','F','D')  profs = []  for u in usernames:    user = UserProfile(full_name=u, gender=random.choice(genders))    profs.append(user)    sess.add(user)  for u in [profs[0], profs[3]]:    for fu in profs:      if u != fu:        u.follow(fu, status=random.choice(fstates))  profs[1].following.append(profs[3]) # doesn't work with followed_by  sess.commit()# uncomment the next line and run script once to create some sample data# create_sample_data(session)profs = session.query(UserProfile).all()print(       '{} follows {}: {}'.format(profs[0], profs[3], profs[3] in profs[0].following))print('{} is followed by {}: {}'.format(profs[0], profs[1], profs[1] in profs[0].followed_by))for p in profs:  print("User: {0}, following: {1}".format(    p.full_name,  ", ".join([f.full_name for f in p.following])))  for f in p.followeds:    print(" " * 25 + "{0} follow.status: '{1}'"          .format(f.followee.full_name, f.status))  print(" followed_by: {1}".format(    p.full_name,  ", ".join([f.full_name for f in p.followed_by])))  for f in p.followers:    print(" " * 25 + "{0} follow.status: '{1}'"          .format(f.follower.full_name, f.status))

为关联对象定义两个关系似乎是必不可少的。该association_proxy方法似乎是不理想的自我指涉的关系调整。的的参数奥德

Follow

构造似乎不符合逻辑的我，但只能这样（是这样解释这里）。

在第117页的Rick Copeland-Essential
Sqlalchemy一书中，您发现有关

secondary

-parameter的以下注释

relationship()

：

请注意，如果使用SQLAlchemy的M：N关系功能，则联接表应 仅
用于将两个表联接在一起，而不用于存储辅助属性。如果需要使用中间联接表来存储关系的其他属性，则应改用两个1：N关系。

抱歉，这有点冗长，但是我喜欢可以直接复制，粘贴和执行的代码。这适用于Python 3.4和SqlAlchemy 0.9，但也可能适用于其他版本。