用戶，組和角色的多對多聲明式SQLAlchemy定義

Question

我是SQLAlchemy的新手，想知道定義這樣的表和關係的最佳方式是什麼。我希望能夠通過user.groups，group.users組中的用戶訪問用戶組，並找出用戶在組中的角色（我假設其將在關聯模型中定義爲邏輯）。我也想選擇所有用戶，按組分組，幷包含角色標題。

我使用教程創建關聯表（聲明樣式）和User和Group類去除secondary參數relationship性能想說，但我會失去直接從用戶訪問組的能力，和用戶直接來自組（關聯表中的backref指向關聯類本身：/）。

任何幫助，將不勝感激。

Answer 1

簡化模型的關鍵是使用associationproxy，因此您一定要檢查一下。
假設用戶可以有一個組內只有一個作用，下面的代碼應該回答你所有的問題：

• 如何配置模型和關係
• 如何添加/刪除/更新角色
• 如何檢索數據（報告），你問

你應該接管模型部分，忘記將R美東時間。下面是完整的包含和工作腳本：

from sqlalchemy import create_engine, Column, Integer, Unicode, ForeignKey 
from sqlalchemy.orm import relationship, scoped_session, sessionmaker 
from sqlalchemy.orm.collections import attribute_mapped_collection 
from sqlalchemy.ext.declarative import declarative_base 
from sqlalchemy.ext.associationproxy import association_proxy 

# Configure test data SA 
engine = create_engine(u'sqlite:///:memory:', echo=False) 
session = scoped_session(sessionmaker(bind=engine, autoflush=False)) 
Base = declarative_base() 

class _BaseMixin(object): 
    """ 
    A helper mixin class to set properties on object creation. 

    Also provides a convenient default __repr__() function, but be aware that 
    also relationships are printed, which might result in loading the relation 
    objects from the database 
    """ 
    def __init__(self, **kwargs): 
     for k, v in kwargs.items(): 
      setattr(self, k, v) 

    def __repr__(self): 
     return "<%s(%s)>" % (self.__class__.__name__, 
      ', '.join('%s=%r' % (k, self.__dict__[k]) 
         for k in sorted(self.__dict__) 
         if '_' != k[0] 
         #if '_sa_' != k[:4] and '_backref_' != k[:9] 
        ) 
      ) 


# relation creator factory functions 
def _creator_gr(group, role): 
    res = UserGroup(group=group, role=role) 
    return res 
def _creator_ur(user, role): 
    res = UserGroup(user=user, role=role) 
    return res 

############################################################################## 
# Object Model 
############################################################################## 
class Role(Base, _BaseMixin): 
    __tablename__ = 'roles' 
    # columns 
    id = Column(Integer, primary_key=True, autoincrement=True) 
    name = Column(Unicode(16), unique=True) 
    # relations 
    usergroup = relationship("UserGroup", backref='role') 

class User(Base, _BaseMixin): 
    __tablename__ = 'users' 
    # columns 
    id = Column(Integer, primary_key=True, autoincrement=True) 
    name = Column(Unicode(16), unique=True) 
    # relations 
    _rel_usergroup = relationship("UserGroup", collection_class=attribute_mapped_collection('group'), 
            cascade='all,delete-orphan', 
            backref='user', 
           ) 
    groups = association_proxy('_rel_usergroup', 'role', creator=_creator_gr) 

class Group(Base, _BaseMixin): 
    __tablename__ = 'groups' 
    # columns 
    id = Column(Integer, primary_key=True, autoincrement=True) 
    name = Column(Unicode(16), unique=True) 
    # relations 
    _rel_usergroup = relationship("UserGroup", collection_class=attribute_mapped_collection('user'), 
            cascade='all,delete-orphan', 
            backref='group', 
           ) 
    users = association_proxy('_rel_usergroup', 'role', creator=_creator_ur) 

class UserGroup(Base, _BaseMixin): 
    __tablename__ = 'user_group' 
    # columns 
    id = Column(Integer, primary_key=True, autoincrement=True) 
    user_id = Column(Integer, ForeignKey('users.id', ondelete='CASCADE'), nullable=False) 
    group_id = Column(Integer, ForeignKey('groups.id', ondelete='CASCADE'), nullable=False) 
    role_id = Column(Integer, ForeignKey('roles.id', ondelete='CASCADE'), nullable=False) 
    # relations 
    # (all backrefs) 



############################################################################## 
# TESTS (showing usages) 
# 
# Requirements: 
# - list all groups of the user: user.groups (use keys) 
# - list all users of the group: group.users (use keys) 
# - get all users ordered (grouped) by group with the role title 
############################################################################## 

def _requirement_get_user_groups(user): 
    return user.groups.keys() 

def _requirement_get_group_users(group): 
    return group.users.keys() 

def _requirement_get_all_users_by_group_with_role(): 
    qry = session.query(Group).order_by(Group.name) 
    res = [] 
    for g in qry.all(): 
     for u, r in sorted(g.users.items()): 
      value = (g.name, u.name, r.name) 
      res.append(value) 
    return res 

def _test_all_requirements(): 
    print '--requirement: all-ordered:' 
    for v in _requirement_get_all_users_by_group_with_role(): 
     print v 

    print '--requirement: user-groups:' 
    for v in session.query(User).order_by(User.id): 
     print v, " has groups: ", _requirement_get_user_groups(v) 

    print '--requirement: group-users:' 
    for v in session.query(Group).order_by(Group.id): 
     print v, " has users: ", _requirement_get_group_users(v) 

# create db schema 
Base.metadata.create_all(engine) 

############################################################################## 
# CREATE TEST DATA 
############################################################################## 

# create entities 
u_peter = User(name='u_Peter') 
u_sonja = User(name='u_Sonja') 
g_sales = Group(name='g_Sales') 
g_wales = Group(name='g_Wales') 
r_super = Role(name='r_Super') 
r_minor = Role(name='r_Minor') 

# helper functions 
def _get_entity(entity, name): 
    return session.query(entity).filter_by(name=name).one() 
def get_user(name): 
    return _get_entity(User, name) 
def get_group(name): 
    return _get_entity(Group, name) 
def _checkpoint(): 
    session.commit() 
    session.expunge_all() 
    _test_all_requirements() 
    session.expunge_all() 
    print '-' * 80 


# test: **ADD** 
u_peter.groups[g_wales] = r_minor # add 
g_wales.users[u_sonja] = r_super # add 
g_sales.users[u_peter] = r_minor # add 
session.add(g_wales) 
#session.add(g_sales) 
_checkpoint() 

# test: **UPDATE** 
u_peter = get_user('u_Peter') 
assert u_peter.name == 'u_Peter' and len(u_peter.groups) == 2 
assert len(u_peter.groups) == 2 
g_wales = get_group('g_Wales') 
g_wales.users[u_peter] = r_super # update 
_checkpoint() 

# test: **DELETE** 
u_peter = get_user('u_Peter') 
assert u_peter.name == 'u_Peter' and len(u_peter.groups) == 2 
g_wales = get_group('g_Wales') 
del u_peter.groups[g_wales] # delete 
_checkpoint()