sqlalchemy(二)高级用法

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本文介绍了SQLAlchemy的高级用法，包括如何在一对多关系中使用外键和relationship，以及如何进行数据添加、查询和删除操作。重点展示了通过join查询和子查询的实现方式，并探讨了表的别名、contains过滤和数据删除等功能。

sqlalchemy(二)高级用法

本文将介绍sqlalchemy的高级用法。

外键以及relationship

首先创建数据库，在这里一个user对应多个address，因此需要在address上增加user_id这个外键（一对多）。

#!/usr/bin/env python
# encoding: utf-8

from sqlalchemy import create_engine
from sqlalchemy import Column
from sqlalchemy import Integer
from sqlalchemy import String
from sqlalchemy import ForeignKey
from sqlalchemy.orm import backref
from sqlalchemy.orm import sessionmaker
from sqlalchemy.orm import relationship, backref
from sqlalchemy.ext.declarative import declarative_base


Base = declarative_base()


class User(Base):
    __tablename__ = 'users'

    id = Column(Integer, primary_key=True)
    name = Column(String(32))

    addresses = relationship("Address", order_by="Address.id", backref="user")


class Address(Base):
    __tablename__ = 'addresses'
    id = Column(Integer, primary_key=True)
    email_address = Column(String(32), nullable=False)
    user_id = Column(Integer, ForeignKey('users.id'))

    #user = relationship("User", backref=backref('addresses', order_by=id))


engine  = create_engine('mysql://root:root@localhost:3306/test', echo=True)
#Base.metadata.create_all(engine)

接下来，调用user和address来添加数据，

>>> jack = User(name='jack')
>>> jack.address
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'User' object has no attribute 'address'
>>> jack.addresses
[]
>>> jack.addresses = [Address(email_address='test@test.com'), Address(email_address='test1@test1.com')]
>>> jack.addresses
[<demo.Address object at 0x7f2536564f90>, <demo.Address object at 0x7f2535dc71d0>]
>>> session.add(jack)
>>> session.commit()
2015-08-19 13:45:36,237 INFO sqlalchemy.engine.base.Engine SHOW VARIABLES LIKE 'sql_mode'
2015-08-19 13:45:36,237 INFO sqlalchemy.engine.base.Engine ()
2015-08-19 13:45:36,238 INFO sqlalchemy.engine.base.Engine SELECT DATABASE()
2015-08-19 13:45:36,238 INFO sqlalchemy.engine.base.Engine ()
2015-08-19 13:45:36,239 INFO sqlalchemy.engine.base.Engine show collation where `Charset` = 'utf8' and `Collation` = 'utf8_bin'
2015-08-19 13:45:36,239 INFO sqlalchemy.engine.base.Engine ()
2015-08-19 13:45:36,239 INFO sqlalchemy.engine.base.Engine SELECT CAST('test plain returns' AS CHAR(60)) AS anon_1
2015-08-19 13:45:36,239 INFO sqlalchemy.engine.base.Engine ()
2015-08-19 13:45:36,240 INFO sqlalchemy.engine.base.Engine SELECT CAST('test unicode returns' AS CHAR(60)) AS anon_1
2015-08-19 13:45:36,240 INFO sqlalchemy.engine.base.Engine ()
2015-08-19 13:45:36,240 INFO sqlalchemy.engine.base.Engine SELECT CAST('test collated returns' AS CHAR CHARACTER SET utf8) COLLATE utf8_bin AS anon_1
2015-08-19 13:45:36,240 INFO sqlalchemy.engine.base.Engine ()
2015-08-19 13:45:36,241 INFO sqlalchemy.engine.base.Engine BEGIN (implicit)
2015-08-19 13:45:36,242 INFO sqlalchemy.engine.base.Engine INSERT INTO users (name) VALUES (%s)
2015-08-19 13:45:36,242 INFO sqlalchemy.engine.base.Engine ('jack',)
2015-08-19 13:45:36,243 INFO sqlalchemy.engine.base.Engine INSERT INTO addresses (email_address, user_id) VALUES (%s, %s)
2015-08-19 13:45:36,243 INFO sqlalchemy.engine.base.Engine ('test@test.com', 1L)
2015-08-19 13:45:36,243 INFO sqlalchemy.engine.base.Engine INSERT INTO addresses (email_address, user_id) VALUES (%s, %s)
2015-08-19 13:45:36,243 INFO sqlalchemy.engine.base.Engine ('test1@test1.com', 1L)
2015-08-19 13:45:36,244 INFO sqlalchemy.engine.base.Engine COMMIT
>>>

此时，查看数据库，可以得到刚才插入的数据，

mysql> select * from users;
+----+------+
| id | name |
+----+------+
|  1 | jack |
+----+------+
1 row in set (0.00 sec)

mysql> select * from addresses;
+----+-----------------+---------+
| id | email_address   | user_id |
+----+-----------------+---------+
|  1 | test@test.com   |       1 |
|  2 | test1@test1.com |       1 |
+----+-----------------+---------+
2 rows in set (0.00 sec)

join查询

如果不使用join的话，可以直接联表查询，

>>> session.query(User.name, Address.email_address).filter(User.id==Address.user_id).filter(Address.email_address=='test@test.com').all()
2015-08-19 14:02:02,877 INFO sqlalchemy.engine.base.Engine SELECT users.name AS users_name, addresses.email_address AS addresses_email_address 
FROM users, addresses 
WHERE users.id = addresses.user_id AND addresses.email_address = %s
2015-08-19 14:02:02,878 INFO sqlalchemy.engine.base.Engine ('test@test.com',)
[('jack', 'test@test.com')]

在sqlalchemy中提供了Queqy.join()函数，

>>> session.query(User).join(Address).filter(Address.email_address=='test@test.com').first()
2015-08-19 14:06:56,624 INFO sqlalchemy.engine.base.Engine SELECT users.id AS users_id, users.name AS users_name 
FROM users INNER JOIN addresses ON users.id = addresses.user_id 
WHERE addresses.email_address = %s 
 LIMIT %s
2015-08-19 14:06:56,624 INFO sqlalchemy.engine.base.Engine ('test@test.com', 1)
<demo.User object at 0x7f9a74139a10>
>>> session.query(User).join(Address).filter(Address.email_address=='test@test.com').first().name
2015-08-19 14:07:04,224 INFO sqlalchemy.engine.base.Engine SELECT users.id AS users_id, users.name AS users_name 
FROM users INNER JOIN addresses ON users.id = addresses.user_id 
WHERE addresses.email_address = %s 
 LIMIT %s
2015-08-19 14:07:04,224 INFO sqlalchemy.engine.base.Engine ('test@test.com', 1)
'jack'
>>> session.query(User).join(Address).filter(Address.email_address=='test@test.com').first().addresses
2015-08-19 14:07:06,534 INFO sqlalchemy.engine.base.Engine SELECT users.id AS users_id, users.name AS users_name 
FROM users INNER JOIN addresses ON users.id = addresses.user_id 
WHERE addresses.email_address = %s 
 LIMIT %s
2015-08-19 14:07:06,534 INFO sqlalchemy.engine.base.Engine ('test@test.com', 1)
2015-08-19 14:07:06,535 INFO sqlalchemy.engine.base.Engine SELECT addresses.id AS addresses_id, addresses.email_address AS addresses_email_address, addresses.user_id AS addresses_user_id 
FROM addresses 
WHERE %s = addresses.user_id ORDER BY addresses.id
2015-08-19 14:07:06,535 INFO sqlalchemy.engine.base.Engine (1L,)
[<demo.Address object at 0x7f9a74139350>, <demo.Address object at 0x7f9a741390d0>]
>>>

注意，上面的用法的前提是存在外键的情况下，如果没有外键，那么可以使用,

query.join(Address, User.id==Address.user_id)    # explicit condition
query.join(User.addresses)                       # specify relationship from left to right
query.join(Address, User.addresses)              # same, with explicit target
query.join('addresses')

表的别名

>>> from sqlalchemy.orm import aliased
>>> adalias1 = aliased(Address)

子查询

假设我们需要这样一个查询，

mysql> SELECT users.*, adr_count.address_count FROM users LEFT OUTER JOIN
    ->     (SELECT user_id, count(*) AS address_count
    ->         FROM addresses GROUP BY user_id) AS adr_count
    ->     ON users.id=adr_count.user_id;
+----+------+---------------+
| id | name | address_count |
+----+------+---------------+
|  1 | jack |             2 |
+----+------+---------------+
1 row in set (0.00 sec)

#　生成子句，等同于（select user_id ... group_by user_id）
>>> sbq = session.query(Address.user_id, func.count('*').label('address_count')).group_by(Address.user_id).subquery()

# 联接子句，注意子句中需要使用c来调用字段内容
>>> session.query(User.name, sbq.c.address_count).outerjoin(sbq, User.id==sbq.c.user_id).all()
2015-08-19 14:42:53,425 INFO sqlalchemy.engine.base.Engine SELECT users.name AS users_name, anon_1.address_count AS anon_1_address_count
FROM users LEFT OUTER JOIN (SELECT addresses.user_id AS user_id, count(%s) AS address_count
FROM addresses GROUP BY addresses.user_id) AS anon_1 ON users.id = anon_1.user_id
2015-08-19 14:42:53,425 INFO sqlalchemy.engine.base.Engine ('*',)
[('jack', 2L)]
>>>

包含contains

query.filter(User.addresses.contains(someaddress))

数据删除delete

>>> session.delete(jack)
>>> session.query(User).filter_by(name='jack').count()
0

外键配置

在上面的例子中，删除了user－jack，但是address中的数据并没有删除。

cascade字段用来

addresses = relationship("Address", backref='user',
    cascade="all, delete, delete-orphan")