在SQLAlchemy中将类映射到多个表

Question

# ! /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类中连接四个表时遇到问题.我正在尝试这个,所以我可以迭代这个类的实例,而不是我从连接ORM表中得到的命名元组.

为什么这一切？因为我已经开始这样了,而且我走得太远,只是离开它.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包含表类的模块.我把它移到了这篇文章的底部,因为也许你甚至都不需要它.

以下只是联接多表类尝试的一个示例.我选择了一个简单的案例,其中只有两个表和一个联结表.在这里,我不会写入这些连接表,但它在其他地方是必要的.这就是为什么类可以很好地解决这个问题.

---

我尝试加入课程,

这是给定的表类模块和这两个网站的示例的组合:

- 针对多个表映射类
- 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))

---

使用此连接类进行不同的表访问

• 这是我尝试在另一个模块中查询此类的方法:

  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']
  

• 然后我通过使用计数器检查,如果查询或我的班级根本不工作.我起床了(计数== 5),所以前两个人加入了桌子.但是当我将条件设置为(count == 6)时,我再次收到第一条错误消息.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]
  """
  

• 然后我检查了每一栏:

  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'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

我尝试了一些其他的东西,这些东西更令人困惑.由于他们没有透露更多信息,我没有添加它们.我不知道我的班级错在哪里.

我想,不知怎的,我必须以某种方式设置类,这只能正确地连接前两个表.但是联接至少部分起作用,因为当'user_groups'表为空时,我也得到了一个空查询.

或者我可能在这个'user_groups'表的映射上做错了.由于连接的某些列是双精度的,因此它们需要一个额外的定义.并且'user_id'已经是人员和用户表的一部分,所以我必须将它映射两次.

我甚至试图从连接中删除'user_groups'表,因为它在关系中(与辅助关系).它给我一个外键错误消息.但也许我只是做错了.

不可否认,我甚至不知道为什么......

rowX.__table__.columns                  # column names as table name suffix 

...有不同的属性名称...

colX in rowX.__table__.columns        # column names without table names

---

额外编辑

• 另一想法!继承可以实现所有这一切吗？每个类都有自己的映射,但是user_groups类可能是必需的.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,因为我甚至无法将它与'groups'或'users'表联系起来.它总是说,类对象没有属性'user_id'.也许这是多对多关系的一部分.

---

附件

这是已经给定的SQLAlchemy模块,带有头,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))

也许下面的脚本创建了数据库,并且已经给出了,在这里证明是有用的.最后一部分是一些测试数据 - 但列之间应该是标签,没有空格.因此,这个脚本也可以在github上找到gist:

-- 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;

---

Answer 1

关于：在对象KeyError中打印的字符串不是键，并且因为您有多个列，所以正在进行一些名称修改。您可能想要这样做，但我建议您打印。repr__table__.columnsid"persons_id""persons.id"__table__.columns.keys()

关于AttributeError： SQLAlchemy 默认情况下将列名直接映射到属性，除非您自己定义属性映射（您就是这样）。事实上，您将id属性定义为column_propertyonpersons.c.id, users.c.id, user_groups.c.user_id意味着这些列不再直接映射到 ORM 类上的属性，但它们仍将位于集合中columns。所以你不能将其用作columns属性名称的可迭代对象。

我没有重现您的所有代码/数据，但我将一个更简单的测试用例与 3 个表（包括 m2m 关系）放在一起来验证这些项目。