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SQLAlchemy Core 使用教程

SQLAlchemy core 是SQLAlchemy的核心部件,主要负责生成sql查询和具体的数据库操作,SQLAlchemy orm 就是构建在core之上的。

在不需要对象映射的时候,使用core而不是orm,可以降低数据库操作成本,提高性能。

Table映射

创建数据库连接

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from sqlalchemy import create_engine
engine = create_engine('sqlite:///test.sqlite3', echo=True)

表结构定义

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from sqlalchemy import Table, Column, Integer, String, MetaData, ForeignKey, Index
metadata = MetaData()
users = Table('users', metadata,
Column('id', Integer, primary_key=True),
Column('name', String),
Column('fullname', String),

# place an index on col1, col2
Index('idx_col12', 'name', 'fullname'), # 添加索引
)

addresses = Table('addresses', metadata,
Column('id', Integer, primary_key=True),
Column('user_id', None, ForeignKey('users.id')),
Column('email_address', String, nullable=False)
)

映射已存在的数据表

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# 单个表
>>> from sqlalchemy import Table , MetaData
>>> metadata = MetaData(engine)
>>> users = Table('users', metadata, autoload=True)
>>> users.c.keys()
['id', 'name', 'fullname']

# 整个数据库
>>> metadata.reflect()
>>> addresses = metadata.tables['addresses']

创建表

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from sqlalchemy import MetaData

metadata = MetaData()
metadata.create_all(engine)

增删查改

插入

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## 获得连接对象
conn = engine.connect()

## 插入一条
ins = users.insert().values(name='jack', fullname='Jack Jones')
conn.execute(ins)

ins = users.insert()
conn.execute(ins, name='wendy', fullname='Wendy Williams')

## 批量插入
conn.execute(addresses.insert(), [
{'user_id': 1, 'email_address' : 'jack@yahoo.com'},
{'user_id': 1, 'email_address' : 'jack@msn.com'},
])

查询

基本查询示例,复杂过滤条件查看文档

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# select * from users
>>> from sqlalchemy.sql import select
>>> cur = conn.execute(select([users]))
>>> cur.fetchall()
[(1, 'jack', 'Jack Jones'), (2, 'wendy', 'Wendy Williams')]

# select name, fullname from users
>>> cur = conn.execute(select([users.c.name, users.c.fullname]))
>>> cur.fetchall()
[('jack', 'Jack Jones'), ('wendy', 'Wendy Williams')]

# select name, fullname from users limit 1
>>> cur = conn.execute(select([users.c.name, users.c.fullname]).limit(1))
>>> cur.fetchall()
[('jack', 'Jack Jones')]

# 联表查询
# SELECT users.name, addresses.email_address FROM users, addresses WHERE users.id = addresses.user_id
>>> s = select([users.c.name, addresses.c.email_address]).where(users.c.id == addresses.c.user_id)
>>> cur = conn.execute(s)
>>> cur.fetchall()
[('jack', 'jack@yahoo.com'), ('jack', 'jack@msn.com')]

# 原始sql语句
>>> from sqlalchemy.sql import text
... s = text(
... "SELECT users.fullname, addresses.email_address AS title "
... "FROM users, addresses "
... "WHERE users.id = addresses.user_id "
... "AND users.name BETWEEN :x AND :y "
... "AND (addresses.email_address LIKE :e1 "
... "OR addresses.email_address LIKE :e2)")
... conn.execute(s, x='m', y='z', e1='%@aol.com', e2='%@msn.com').fetchall()

更改

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>>> from sqlalchemy.sql import update, select, delete, insert
# 更改为具体值
>>> stmt = users.update().\
... where(users.c.name == 'jack').\
... values(name='ed')
>>> conn.execute(stmt)

# 更改为另一个字段的值
>>> stmt = users.update().values(name=users.c.fullname)
>>> conn.execute(stmt)

删除

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>>> stmt = users.delete().where(users.c.id == 1)
>>> conn.execute(stmt)