sqlalchemy(二)高级用法
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sqlalchemy(二)高级用法
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本文將介紹sqlalchemy的高級用法。
外鍵以及relationship
首先創(chuàng)建數(shù)據(jù)庫，在這里一個user對應多個address，因此需要在address上增加user_id這個外鍵（一對多）。
#!/usr/bin/env python # encoding: utf-8from 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)接下來，調用user和address來添加數(shù)據(jù)，
此時，查看數(shù)據(jù)庫，可以得到剛才插入的數(shù)據(jù)，
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查詢
如果不使用join的話，可以直接聯(lián)表查詢，
>>> 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()函數(shù)，
>>> 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鍵的情況下，如果沒有外鍵，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')表的別名
子查詢
假設我們需要這樣一個查詢，
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)包含contains
query.filter(User.addresses.contains(someaddress))數(shù)據(jù)刪除delete
>>> session.delete(jack) >>> session.query(User).filter_by(name='jack').count() 0外鍵配置
在上面的例子中，刪除了user－jack，但是address中的數(shù)據(jù)并沒有刪除。
cascade字段用來
addresses = relationship("Address", backref='user',cascade="all, delete, delete-orphan")轉載于:https://www.cnblogs.com/ExMan/p/10313733.html
總結
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