sqlalchemy(一)基本操作

sqlalchemy采用簡單的Python語言，為高效和高性能的數據庫訪問設計，實現了完整的企業級持久模型。

安裝

1. 需要安裝MySQLdb
2. pip install sqlalchemy

安裝完成后，執行

>>>import sqlalchemy
>>>sqlalchemy.__version__

連接數據庫

在sqlalchemy中，session用於創建程序與數據庫之間的會話。所有對象的載入和保存都需要通過session對象。

from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker

engine = create_engine('mysql://user:passwd@ip:port/db', echo=True)
Session = sessionmaker(bind=engine)

session = Session()
session.execute('show databases')

其中，echo為True代表打開logging。

創建一個映射

一個映射對應着一個Python類，用來表示一個表的結構。下面創建一個person表，包括id和name兩個字段。

from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()

class Person(Base):
    __tablename__ = 'person'

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

    def __repr__(self):
        return "<Person(name='%s')>" % self.name

添加數據

#創建一個person對象
person = Person(name='jack')
#添加person對象，但是仍然沒有commit到數據庫
session.add(person)
#commit操作
session.commit()

如何獲取id的？

>>> person = Person(name='ilis')
>>> person.id #此時還沒有commit到mysql,因此無id
>>> session.add(person)
>>> person.id #同上
>>> session.commit()
2015-08-18 23:08:23,530 INFO sqlalchemy.engine.base.Engine INSERT INTO person (name) VALUES (%s)
2015-08-18 23:08:23,531 INFO sqlalchemy.engine.base.Engine ('ilis',)
2015-08-18 23:08:23,532 INFO sqlalchemy.engine.base.Engine COMMIT
>>> person.id #commit后，可以獲取該對象的id
2015-08-18 23:08:27,556 INFO sqlalchemy.engine.base.Engine BEGIN (implicit)
2015-08-18 23:08:27,557 INFO sqlalchemy.engine.base.Engine SELECT person.id AS person_id, person.name AS person_name
FROM person
WHERE person.id = %s
2015-08-18 23:08:27,557 INFO sqlalchemy.engine.base.Engine (5L,)
5L
>>>

添加多個數據

session.add_all([
    Person(name='jack'),
    Person(name='mike')
])
session.commit()

回滾

>>> person = Person(name='test')
>>> session.add(person)
>>> session.query(person).filter(name=='test')
>>> session.query(Person).filter(Person.name=='test').all()
2015-08-18 23:13:23,265 INFO sqlalchemy.engine.base.Engine INSERT INTO person (name) VALUES (%s)
2015-08-18 23:13:23,265 INFO sqlalchemy.engine.base.Engine ('test',)
2015-08-18 23:13:23,267 INFO sqlalchemy.engine.base.Engine SELECT person.id AS person_id, person.name AS person_name
FROM person
WHERE person.name = %s
2015-08-18 23:13:23,267 INFO sqlalchemy.engine.base.Engine ('test',)
[<demo.Person object at 0x7f4e37730510>]
>>> session.rollback()
2015-08-18 23:13:37,496 INFO sqlalchemy.engine.base.Engine ROLLBACK
>>> session.query(Person).filter(Person.name=='test').all()
2015-08-18 23:13:38,690 INFO sqlalchemy.engine.base.Engine BEGIN (implicit)
2015-08-18 23:13:38,691 INFO sqlalchemy.engine.base.Engine SELECT person.id AS person_id, person.name AS person_name
FROM person
WHERE person.name = %s
2015-08-18 23:13:38,692 INFO sqlalchemy.engine.base.Engine ('test',)
[]
>>>

數據查詢

使用Session的query()方法。

#獲取所有數據
session.query(Person).all()

#獲取某一列數據,類似於django的get,如果返回數據為多個則報錯
session.query(Person).filter(Person.name=='jack').one()

#獲取返回數據的第一行
session.query(Person).first()

#過濾數據
session.query(Person.name).filter(Person.id>1).all()

#limit
session.query(Person).all()[1:3]

#order by
session.query(Person).ordre_by(-Person.id)

#equal/like/in
query = session.query(Person)
query.filter(Person.id==1).all()
query.filter(Person.id!=1).all()
query.filter(Person.name.like('%ac%')).all()
query.filter(Person.id.in_([1,2,3])).all()
query.filter(~Person.id.in_([1,2,3])).all()
query.filter(Person.name==None).all()

#and or
from sqlalchemy import and_
query.filter(and_(Person.id==1, Person.name=='jack')).all()
query.filter(Person.id==1, Person.name=='jack').all()
query.filter(Person.id==1).filter(Person.name=='jack').all()
from sqlalchemy import or_
query.filter(or_(Person.id==1, Person.id==2)).all()

使用text

from sqlalchemy import text
query.filter(text("id>1")).all()
query.filter(Person.id>1).all() #同上
query.filter(text("id>:id")).params(id=1).all() #使用:，params來傳參

query.from_statement(
    text("select * from person where name=:name")).\
    params(name='jack').all()

計數

Query使用count()函數來實現查詢計數。

query.filter(Person.id>1).count()

group by的用法

from sqlalchemy import func
session.query(func.count(Person.name), Person.name),group_by(Person.name).all()

實現count(*)來查詢表內行數

session.query(func.count('*')).select_from(Person).scalar()
session.query(func.count(Person.id)).scalar()