SQLAlchemy
介绍
SQLAlchemy是一个基于Python实现的ORM框架。该框架建立在 DB API之上,使用关系对象映射进行数据库操作,简言之便是:将类和对象转换成SQL,然后使用数据API执行SQL并获取执行结果。
安装:
pip install sqlalchemy
组成部分:
- Engine,框架的引擎
- Connection Pooling ,数据库连接池
- Dialect,选择连接数据库的DB API种类
- Schema/Types,架构和类型
- SQL Exprression Language,SQL表达式语言
SQLAlchemy本身无法操作数据库,其必须以来pymsql等第三方插件,Dialect用于和数据API进行交流,根据配置文件的不同调用不同的数据库API,从而实现对数据库的操作,如:
MySQL-Python mysql+mysqldb://<user>:<password>@<host>[:<port>]/<dbname> pymysql mysql+pymysql://<username>:<password>@<host>/<dbname>[?<options>] MySQL-Connector mysql+mysqlconnector://<user>:<password>@<host>[:<port>]/<dbname> cx_Oracle oracle+cx_oracle://user:pass@host:port/dbname[?key=value&key=value...] 更多:http://docs.sqlalchemy.org/en/latest/dialects/index.html
使用
1.执行原生SQL
import time import threading import sqlalchemy from sqlalchemy import create_engine from sqlalchemy.engine.base import Engine engine = create_engine( "mysql+pymysql://root:123@127.0.0.1:3306/t1?charset=utf8", max_overflow=0, # 超过连接池大小外最多创建的连接 pool_size=5, # 连接池大小 pool_timeout=30, # 池中没有线程最多等待的时间,否则报错 pool_recycle=-1 # 多久之后对线程池中的线程进行一次连接的回收(重置) ) def task(arg): conn = engine.raw_connection() cursor = conn.cursor() cursor.execute( "select * from t1" ) result = cursor.fetchall() cursor.close() conn.close() for i in range(20): t = threading.Thread(target=task, args=(i,)) t.start()
2.ORM
创建表
import datetime from sqlalchemy import create_engine from sqlalchemy.ext.declarative import declarative_base from sqlalchemy import Column, Integer, String, DateTime, UniqueConstraint, Index Base = declarative_base() class User(Base): __tablename__ = 'users' # 表名 __table_args__ = { 'mysql_engine': 'InnoDB', 'mysql_charset': 'utf8' } id = Column(Integer, primary_key=True) name = Column(String(32), index=True, nullable=False) email = Column(String(32), unique=True) ctime = Column(DateTime, default=datetime.datetime.now) # __table_args__ = ( # UniqueConstraint('id', 'name', name='uq_id_name'), # 联合唯一 # Index('') # 索引 # ) engine = create_engine( "mysql+pymysql://root:123456@127.0.0.1:3306/day145?charset=utf8", max_overflow=0, # 超过连接池大小后最多再创建的连接数 pool_size=5, # 连接池大小 pool_timeout=30, # 设置连接池中没有线程后最多等待的时间 pool_recycle=-1, # 多久之后对连接池中的线程进行一次连接的回收 ) def init_db(): ''' 根据类创建数据库表 :return: ''' Base.metadata.create_all(engine) def drop_db(): ''' 根据类删除数据库表 :return: ''' Base.metadata.drop_all(engine) if __name__ == '__main__': init_db()
#!/usr/bin/env python # -*- coding: utf-8 -*- __author__ = 'Wu' from sqlalchemy import create_engine from sqlalchemy.ext.declarative import declarative_base from sqlalchemy import Column, Integer, String, ForeignKey from sqlalchemy.orm import relationship Base = declarative_base() class Hobby(Base): __tablename__ = 'hobby' id = Column(Integer, primary_key=True) caption = Column(String(32), default='羽毛球') class Person(Base): __tablename__ = 'person' __mapper_args__ = {'column_prefix': 'ch_'} # 为列名设置前缀 id = Column(Integer, primary_key=True) name = Column(String(32), index=True, nullable=True) hobby_id = Column(Integer, ForeignKey('hobby.id')) hobby = relationship('hobby', backref='person') engine = create_engine( "mysql+pymysql://root:123456@127.0.0.1:3306/day145?charset=utf8", max_overflow=0, # 超过连接池大小后最多再创建的连接数 pool_size=5, # 连接池大小 pool_timeout=30, # 设置连接池中没有线程后最多等待的时间 pool_recycle=-1, # 多久之后对连接池中的线程进行一次连接的回收 ) def init_db(): Base.metadata.create_all(engine) def drop_db(): Base.metadata.drop_all(engine) init_db()
#!/usr/bin/env python # -*- coding: utf-8 -*- __author__ = 'Wu' class Server2Group(Base): __tablename__ = 'server2group' id = Column(Integer, primary_key=True, autoincrement=True) server_id = Column(Integer, ForeignKey('server.id')) group_id = Column(Integer, ForeignKey('group.id')) class Group(Base): __tablename__ = 'group' id = Column(Integer, primary_key=True) name = Column(String(64), unique=True, nullable=False) # 与生成表结构无关,仅用于查询方便 servers = relationship('Server', secondary='server2group', backref='groups') class Server(Base): __tablename__ = 'server' id = Column(Integer, primary_key=True, autoincrement=True) hostname = Column(String(64), unique=True, nullable=False engine = create_engine( "mysql+pymysql://root:123456@127.0.0.1:3306/day145?charset=utf8", max_overflow=0, # 超过连接池大小后最多再创建的连接数 pool_size=5, # 连接池大小 pool_timeout=30, # 设置连接池中没有线程后最多等待的时间 pool_recycle=-1, # 多久之后对连接池中的线程进行一次连接的回收 ) def init_db(): Base.metadata.create_all(engine) def drop_db(): Base.metadata.drop_all(engine) init_db()
查询