# ! /usr/bin/env python
# -*- coding: utf-8 -*-
# login_frontend.py
""" Python 2.7.3
Cherrypy 3.2.2
PostgreSQL 9.1
psycopy2 2.4.5
SQLAlchemy 0.7.10
"""
我在一个 Python/SQLAlchemy 类中加入四个表时遇到问题。我正在尝试这个，所以我可以迭代这个类的实例，而不是通过使用 ORM 连接表获得的命名元组。
为什么这一切？因为我已经开始这样做了，而且我走得太远了，不能离开它。此外，它必须是可能的，所以我想知道它是如何完成的。
对于这个项目（cherrypy web-frontend），我得到了一个已经完成的带有表格类的模块。我把它移到了这篇文章的底部，因为也许你甚至不需要它。
以下只是连接多个表类尝试的一个示例。我选择了一个简单的案例，其中不仅有两张桌子和一张连接桌子。在这里，我不会写入这些连接表，但在其他地方是必要的。这就是为什么类将是解决这个问题的好方法。
我尝试加入课程，
这是给定表类模块和这两个网站的示例的组合：
-将一个类映射到多个表
- SQLAlchemy：一个类 - 两个表
class JoinUserGroupPerson (Base):
persons = md.tables['persons']
users = md.tables['users']
user_groups = md.tables['user_groups']
groups = md.tables['groups']
user_group_person =(
join(persons, users, persons.c.id == users.c.id).
join(user_groups, users.c.id == user_groups.c.user_id).
join(groups, groups.c.id == user_groups.c.group_id))
__table__ = user_group_person
""" I expanded the redefinition of 'id' to three tables,
and removed this following one, since it made no difference:
users_id = column_property(users.c.id, user_groups.c.user_id)
"""
id = column_property(persons.c.id, users.c.id, user_groups.c.user_id)
groups_id = column_property(groups.c.id, user_groups.c.group_id)
groups_name = groups.c.name
def __init__(self, group_name, login, name, email=None, phone=None):
self.groups_name = group_name
self.login = login
self.name = name
self.email = email
self.phone = phone
def __repr__(self):
return(
"<JoinUserGroupPerson('%s', '%s', '%s', '%s', '%s')>" %(
self.groups_name, self.login, self.name, self.email, self.phone))
此连接类的不同表访问
这就是我尝试在另一个模块中查询此类的方式：
pg = sqlalchemy.create_engine( 'postgresql://{}:{}@{}:{}/{}'. format(user, password, server, port, data)) Session = sessionmaker(bind=pg) s1 = Session() query = (s1.query(JoinUserGroupPerson). filter(JoinUserGroupPerson.login==user). order_by(JoinUserGroupPerson.id)) record = {} for rowX in query: for colX in rowX.__table__.columns: record[column.name] = getattr(rowX,colX.name) """ RESULT: """ Traceback (most recent call last): File "/usr/local/lib/python2.7/dist-packages/cherrypy/_cprequest.py", line 656, in respond response.body = self.handler() File "/usr/local/lib/python2.7/dist-packages/cherrypy/lib/encoding.py", line 228, in __call__ ct.params['charset'] = self.find_acceptable_charset() File "/usr/local/lib/python2.7/dist-packages/cherrypy/lib/encoding.py", line 134, in find_acceptable_charset if encoder(encoding): File "/usr/local/lib/python2.7/dist-packages/cherrypy/lib/encoding.py", line 86, in encode_string for chunk in self.body: File "XXX.py", line YYY, in ZZZ record[colX.name] = getattr(rowX,colX.name) AttributeError: 'JoinUserGroupPerson' object has no attribute 'user_id'然后我检查了表属性：
for rowX in query: return (u'{}'.format(rowX.__table__.columns)) """ RESULT: """ ['persons.id', 'persons.name', 'persons.email', 'persons.phone', 'users.id', 'users.login', 'user_groups.user_id', 'user_groups.group_id', 'groups.id', 'groups.name']然后，我使用计数器检查了查询或我的课程是否根本不起作用。我起床（计数 == 5），所以前两个连接表。但是当我将条件设置为 (count == 6) 时，我又收到了第一条错误消息。AttributeError：“JoinUserGroupPerson”对象没有属性“user_id”。：
list = [] for rowX in query: for count, colX in enumerate(rowX.__table__.columns): list.append(getattr(rowX,colX.name)) if count == 5: break return (u'{}'.format(list)) """ RESULT: """ [4, u'user real name', None, None, 4, u'user'] """ which are these following six columns: persons[id, name, email, phone], users[id, login] """然后我检查了每一列：
list = [] for rowX in query: for colX in rowX.__table__.columns: list.append(colX) return (u'{}'.format(list)) """ RESULT: """ [Column(u'id', INTEGER(), table=, primary_key=True, nullable=False, server_default=DefaultClause(, for_update=False)), Column(u'name', VARCHAR(length=252), table=, nullable=False), Column(u'email', VARCHAR(), table=), Column(u'phone', VARCHAR(), table=), Column(u'id', INTEGER(), ForeignKey(u'persons.id'), table=, primary_key=True, nullable=False), Column(u'login', VARCHAR(length=60), table=, nullable=False), Column(u'user_id', INTEGER(), ForeignKey(u'users.id'), table=, primary_key=True, nullable=False), Column(u'group_id', INTEGER(), ForeignKey(u'groups.id'), table=, primary_key=True, nullable=False), Column(u'id', INTEGER(), table=, primary_key=True, nullable=False), Column(u'name', VARCHAR(length=60), table=, nullable=False)]然后我尝试了另外两个直接访问，这让我得到了 'id' 和 'persons.id' 的 KeyErrors：
for rowX in query: return (u'{}'.format(rowX.__table__.columns['id'].name)) for rowX in query: return (u'{}'.format(rowX.__table__.columns['persons.id'].name))
结论
我尝试了其他一些事情，这些事情更加令人困惑。由于他们没有透露更多信息，我没有添加它们。我看不出我的班级哪里错了。
我想，不知何故，我必须以某种方式设置类，它只会正确连接前两个表。但连接至少部分有效，因为当“user_groups”表为空时，我也得到了一个空查询。
或者也许我对这个“user_groups”表的映射做错了。由于使用连接，一些列是双列，它们需要一个额外的定义。'user_id' 已经是 person 和 users 表的一部分，所以我不得不映射它两次。
我什至尝试从联接中删除“user_groups”表，因为它在关系中（与辅助）。它给了我一个外键错误消息。但也许我只是做错了。
诚然，我什至不知道为什么......
rowX.__table__.columns # column names as table name suffix
...具有与...不同的属性名称
colX in rowX.__table__.columns # column names without table names
额外编辑
另一个想法！所有这一切都可以通过继承实现吗？每个类都有自己的映射，但可能需要 user_groups 类。连接必须在单个类之间。init() 和 repr() 仍然需要重新定义。
它可能与“user_groups”表有关，因为我什至无法将它与“groups”或“users”表连接起来。它总是说，类对象没有属性'user_id'。也许这与多对多关系有关。
附件
这是已经给出的 SQLAlchemy 模块，带有标题，没有关于数据库的特定信息，以及连接表的类：
#!/usr/bin/python
# vim: set fileencoding=utf-8 :
import sqlalchemy
from sqlalchemy import join
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import relationship, backref, column_property
pg = sqlalchemy.create_engine(
'postgresql://{}@{}:{}/{}'.format(user, host, port, data))
md = sqlalchemy.MetaData(pg, True)
Base = declarative_base()
""" ... following, three of the four joined tables.
UserGroups isn't necessary, so it wasn't part of the module.
And the other six classes shouldn't be important for this ...
"""
class Person(Base):
__table__ = md.tables['persons']
def __init__(self, name, email=None, phone=None):
self.name = name
self.email = email
self.phone = phone
def __repr__(self):
return(
"<Person(%s, '%s', '%s', '%s')>" %(
self.id, self.name, self.email, self.phone))
class Group(Base):
__table__ = md.tables['groups']
def __init__(self, name):
self.name = name
def __repr__(self):
return("<Group(%s, '%s')>" %(self.id, self.name))
class User(Base):
__table__ = md.tables['users']
person = relationship('Person')
groups = relationship(
'Group', secondary=md.tables['user_groups'], order_by='Group.id',
backref=backref('users', order_by='User.login'))
def __init__(self, person, login):
if isinstance(person, Person):
self.person = person
else:
self.id = person
self.login = login
def __repr__(self):
return("<User(%s, '%s')>" %(self.id, self.login))
也许下面的脚本，它创建了数据库，也已经给出，在这里会证明是有用的。最后一部分是一些测试数据——但列之间应该是制表符，没有空格。因此，这个脚本也可以在 github 上作为 gist找到：
-- file create_str.sql
-- database creation script
-- central script for creating all database objects
-- set the database name
\set strdbname logincore
\c admin
BEGIN;
\i str_roles.sql
COMMIT;
DROP DATABASE IF EXISTS :strdbname;
CREATE DATABASE :strdbname TEMPLATE template1 OWNER str_db_owner
ENCODING 'UTF8';
\c :strdbname
SET ROLE str_db_owner;
BEGIN;
\i str.sql
COMMIT;
RESET ROLE;
-- file str_roles.sql
-- create roles for the database
-- owner of the database objects
SELECT create_role('str_db_owner', 'NOINHERIT');
-- role for using
SELECT create_role('str_user');
-- make str_db_owner member in all relevant roles
GRANT str_user TO str_db_owner WITH ADMIN OPTION;
-- file str.sql
-- creation of database
-- prototypes
\i str_prototypes.sql
-- domain for non empty text
CREATE DOMAIN ntext AS text CHECK (VALUE<>'');
-- domain for email addresses
CREATE DOMAIN email AS varchar(252) CHECK (is_email_address(VALUE));
-- domain for phone numbers
CREATE DOMAIN phone AS varchar(60) CHECK (is_phone_number(VALUE));
-- persons
CREATE TABLE persons (
id serial PRIMARY KEY,
name varchar(252) NOT NULL,
email email,
phone phone
);
GRANT SELECT, INSERT, UPDATE, DELETE ON persons TO str_user;
GRANT USAGE ON SEQUENCE persons_id_seq TO str_user;
CREATE TABLE groups (
id integer PRIMARY KEY,
name varchar(60) UNIQUE NOT NULL
);
GRANT SELECT ON groups TO str_user;
-- database users
CREATE TABLE users (
id integer PRIMARY KEY REFERENCES persons(id) ON UPDATE CASCADE,
login varchar(60) UNIQUE NOT NULL
);
GRANT SELECT ON users TO str_user;
-- user <-> groups
CREATE TABLE user_groups (
user_id integer NOT NULL REFERENCES users(id)
ON UPDATE CASCADE ON DELETE CASCADE,
group_id integer NOT NULL REFERENCES groups(id)
ON UPDATE CASCADE ON DELETE CASCADE,
PRIMARY KEY (user_id, group_id)
);
-- functions
\i str_functions.sql
-- file str_prototypes.sql
-- prototypes for database
-- simple check for correct email address
CREATE FUNCTION is_email_address(email varchar) RETURNS boolean
AS $CODE$
SELECT FALSE
$CODE$ LANGUAGE sql IMMUTABLE STRICT;
-- simple check for correct phone number
CREATE FUNCTION is_phone_number(nr varchar) RETURNS boolean
AS $CODE$
SELECT FALSE
$CODE$ LANGUAGE sql IMMUTABLE STRICT;
-- file str_functions.sql
-- functions for database
-- simple check for correct email address
CREATE OR REPLACE FUNCTION is_email_address(email varchar) RETURNS boolean
AS $CODE$
SELECT $1 ~ E'^[A-Za-z0-9.!#$%&\'\*\+\-/=\?\^_\`{\|}\~\.]+@[-a-z0-9\.]+$'
$CODE$ LANGUAGE sql IMMUTABLE STRICT;
-- simple check for correct phone number
CREATE OR REPLACE FUNCTION is_phone_number(nr varchar) RETURNS boolean
AS $CODE$
SELECT $1 ~ E'^[-+0-9\(\)/ ]+$'
$CODE$ LANGUAGE sql IMMUTABLE STRICT;
-- file fill_str_test.sql
-- test data for database
-- between the columns are supposed to be tabs, no spaces !!!
BEGIN;
COPY persons (id, name, email) FROM STDIN;
1 Joseph Schneider jschneid@lab.uni.de
2 Test User jschneid@lab.uni.de
3 Hans Dampf \N
\.
SELECT setval('persons_id_seq', (SELECT max(id) FROM persons));
COPY groups (id, name) FROM STDIN;
1 IT
2 SSG
\.
COPY users (id, login) FROM STDIN;
1 jschneid
2 tuser
3 dummy
\.
COPY user_groups (user_id, group_id) FROM STDIN;
1 1
2 1
3 2
\.
COMMIT;