Python操作MySQL（二） ORM篇

標籤：msyql orm   sqlalchemy   

SQLAlchemy是Python程式設計語言下的一款ORM架構，該架構建立在資料庫API之上，使用關聯性物件映射進行資料庫操作，簡言之便是：將對象轉換成SQL，然後使用資料API執行SQL並擷取執行結果。

一、安裝

pip3 install SQLAlchemy

SQLAlchemy本身無法操作資料庫，其必須以來pymsql等第三方外掛程式，Dialect用於和資料API進行交流，根據設定檔的不同調用不同的資料庫API，從而實現對資料庫的操作，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:[email protected]:port/dbname[?key=value&key=value...]更多詳見：http://docs.sqlalchemy.org/en/latest/dialects/index.html

二、內部處理

使用 Engine/ConnectionPooling/Dialect 進行資料庫操作，Engine使用ConnectionPooling串連資料庫，然後再通過Dialect執行SQL語句。

#!/usr/bin/env python# -*- coding:utf-8 -*-from sqlalchemy import create_engine# 處理中文# sqlalchemy設定編碼字元集一定要在資料庫訪問的URL上增加charset=utf8，否則資料庫的串連就不是utf8的編碼格式engine = create_engine("mysql+pymysql://root:[email protected]:3306/t1?charset=utf8‘", max_overflow=5, echo=True)# 執行SQL# cur = engine.execute(#     "INSERT INTO hosts (host, color_id) VALUES (‘1.1.1.22‘, 3)"# )# 新插入行自增ID# cur.lastrowid# 執行SQL# cur = engine.execute(#     "INSERT INTO hosts (host, color_id) VALUES(%s, %s)",[(‘1.1.1.22‘, 3),(‘1.1.1.221‘, 3),]# )# 執行SQL# cur = engine.execute(#     "INSERT INTO hosts (host, color_id) VALUES (%(host)s, %(color_id)s)",#     host=‘1.1.1.99‘, color_id=3# )# 執行SQL# cur = engine.execute(‘select * from hosts‘)# 擷取第一行資料# cur.fetchone()# 擷取第n行資料# cur.fetchmany(3)# 擷取所有資料

三、ORM功能使用

使用 ORM/Schema Type/SQL Expression Language/Engine/ConnectionPooling/Dialect 所有組件對資料進行操作。根據類建立對象，對象轉換成SQL，執行SQL。

1、建立表

#!/usr/bin/env python# -*- coding:utf-8 -*-from sqlalchemy.ext.declarative import declarative_basefrom sqlalchemy import Column, Integer, String, ForeignKey, UniqueConstraint, Indexfrom sqlalchemy.orm import sessionmaker, relationshipfrom sqlalchemy import create_engineengine = create_engine("mysql+pymysql://root:[email protected]:3306/t1", max_overflow=5)Base = declarative_base()# 建立單表class Users(Base):    __tablename__ = ‘users‘    id = Column(Integer, primary_key=True)    name = Column(String(32))    extra = Column(String(16))    __table_args__ = (    UniqueConstraint(‘id‘, ‘name‘, name=‘uix_id_name‘),        Index(‘ix_id_name‘, ‘name‘, ‘extra‘),    )# 一對多class Favor(Base):    __tablename__ = ‘favor‘    nid = Column(Integer, primary_key=True)    caption = Column(String(50), default=‘red‘, unique=True)class Person(Base):    __tablename__ = ‘person‘    nid = Column(Integer, primary_key=True)    name = Column(String(32), index=True, nullable=True)    favor_id = Column(Integer, ForeignKey("favor.nid"))# 多對多class Group(Base):    __tablename__ = ‘group‘    id = Column(Integer, primary_key=True)    name = Column(String(64), unique=True, nullable=False)    port = Column(Integer, default=22)class Server(Base):    __tablename__ = ‘server‘    id = Column(Integer, primary_key=True, autoincrement=True)    hostname = Column(String(64), unique=True, nullable=False)class ServerToGroup(Base):    __tablename__ = ‘servertogroup‘    nid = Column(Integer, primary_key=True, autoincrement=True)    server_id = Column(Integer, ForeignKey(‘server.id‘))    group_id = Column(Integer, ForeignKey(‘group.id‘))def init_db():    Base.metadata.create_all(engine)def drop_db():    Base.metadata.drop_all(engine)註：設定外檢的另一種方式 ForeignKeyConstraint([‘other_id‘], [‘othertable.other_id‘])

2、動作表

表結構 + 資料庫連接

#!/usr/bin/env python# -*- coding:utf-8 -*-from sqlalchemy.ext.declarative import declarative_basefrom sqlalchemy import Column, Integer, String, ForeignKey, UniqueConstraint, Indexfrom sqlalchemy.orm import sessionmaker, relationshipfrom sqlalchemy import create_engineengine = create_engine("mysql+pymysql://root:[email protected]:3306/t1", max_overflow=5)Base = declarative_base()# 建立單表class Users(Base):    __tablename__ = ‘users‘    id = Column(Integer, primary_key=True)    name = Column(String(32))    extra = Column(String(16))    __table_args__ = (    UniqueConstraint(‘id‘, ‘name‘, name=‘uix_id_name‘),        Index(‘ix_id_name‘, ‘name‘, ‘extra‘),    )    def __repr__(self):        return "%s-%s" %(self.id, self.name)# 一對多class Favor(Base):    __tablename__ = ‘favor‘    nid = Column(Integer, primary_key=True)    caption = Column(String(50), default=‘red‘, unique=True)    def __repr__(self):        return "%s-%s" %(self.nid, self.caption)class Person(Base):    __tablename__ = ‘person‘    nid = Column(Integer, primary_key=True)    name = Column(String(32), index=True, nullable=True)    favor_id = Column(Integer, ForeignKey("favor.nid"))    # 與產生表結構無關，僅用於查詢方便    favor = relationship("Favor", backref=‘pers‘)# 多對多class ServerToGroup(Base):    __tablename__ = ‘servertogroup‘    nid = Column(Integer, primary_key=True, autoincrement=True)    server_id = Column(Integer, ForeignKey(‘server.id‘))    group_id = Column(Integer, ForeignKey(‘group.id‘))    group = relationship("Group", backref=‘s2g‘)    server = relationship("Server", backref=‘s2g‘)class Group(Base):    __tablename__ = ‘group‘    id = Column(Integer, primary_key=True)    name = Column(String(64), unique=True, nullable=False)    port = Column(Integer, default=22)    # group = relationship(‘Group‘,secondary=ServerToGroup,backref=‘host_list‘)class Server(Base):    __tablename__ = ‘server‘    id = Column(Integer, primary_key=True, autoincrement=True)    hostname = Column(String(64), unique=True, nullable=False)def init_db():    Base.metadata.create_all(engine)def drop_db():    Base.metadata.drop_all(engine)Session = sessionmaker(bind=engine)session = Session()

• 增

obj = Users(name="alex0", extra=‘sb‘)session.add(obj)session.add_all([    Users(name="alex1", extra=‘sb‘),    Users(name="alex2", extra=‘sb‘),])session.commit()

• 刪

session.query(Users).filter(Users.id > 2).delete()session.commit()

• 改

session.query(Users).filter(Users.id > 2).update({"name" : "099"})session.query(Users).filter(Users.id > 2).update({Users.name: Users.name + "099"}, synchronize_session=False)session.query(Users).filter(Users.id > 2).update({"num": Users.num + 1}, synchronize_session="evaluate")session.commit()

• 查

ret = session.query(Users).all()ret = session.query(Users.name, Users.extra).all()ret = session.query(Users).filter_by(name=‘alex‘).all()ret = session.query(Users).filter_by(name=‘alex‘).first()ret = session.query(Users).filter(text("id<:value and name=:name")).params(value=224, name=‘fred‘).order_by(User.id).all()ret = session.query(Users).from_statement(text("SELECT * FROM users where name=:name")).params(name=‘ed‘).all()

• 其他動作

#　條件ret = session.query(Users).filter_by(name=‘alex‘).all()ret = session.query(Users).filter(Users.id > 1, Users.name == ‘eric‘).all()ret = session.query(Users).filter(Users.id.between(1, 3), Users.name == ‘eric‘).all()ret = session.query(Users).filter(Users.id.in_([1,3,4])).all()ret = session.query(Users).filter(~Users.id.in_([1,3,4])).all()ret = session.query(Users).filter(Users.id.in_(session.query(Users.id).filter_by(name=‘eric‘))).all()from sqlalchemy import and_, or_ret = session.query(Users).filter(and_(Users.id > 3, Users.name == ‘eric‘)).all()ret = session.query(Users).filter(or_(Users.id < 2, Users.name == ‘eric‘)).all()ret = session.query(Users).filter(    or_(        Users.id < 2,        and_(Users.name == ‘eric‘, Users.id > 3),        Users.extra != ""    )).all()# 萬用字元ret = session.query(Users).filter(Users.name.like(‘e%‘)).all()ret = session.query(Users).filter(~Users.name.like(‘e%‘)).all()# 限制ret = session.query(Users)[1:2]# 排序ret = session.query(Users).order_by(Users.name.desc()).all()ret = session.query(Users).order_by(Users.name.desc(), Users.id.asc()).all()# 分組from sqlalchemy.sql import funcret = session.query(Users).group_by(Users.extra).all()ret = session.query(    func.max(Users.id),    func.sum(Users.id),    func.min(Users.id)).group_by(Users.name).all()ret = session.query(    func.max(Users.id),    func.sum(Users.id),    func.min(Users.id)).group_by(Users.name).having(func.min(Users.id) >2).all()# 連表ret = session.query(Users, Favor).filter(Users.id == Favor.nid).all()ret = session.query(Person).join(Favor).all()ret = session.query(Person).join(Favor, isouter=True).all()# 組合q1 = session.query(Users.name).filter(Users.id > 2)q2 = session.query(Favor.caption).filter(Favor.nid < 2)ret = q1.union(q2).all()q1 = session.query(Users.name).filter(Users.id > 2)q2 = session.query(Favor.caption).filter(Favor.nid < 2)ret = q1.union_all(q2).all()

Python操作MySQL（二） ORM篇