数据库(四): ORM, SQLAlchemy

'''
SQLAlchemy:
           1. 架构和流程
 2. 建表
 3. 操作
''' # 综述

'''
SQLAlchemy架构和操作流程:
 1. 架构
 ORM(Object Relational Mapper)
 ----------------------------------------------------------
 Schema/Types, SQL Language, Engine(Connection Pool,Dialect)
 ----------------------------------------------------------
 DBAPI (pymysql,mysqldb,mysqlconnector)
 2. 流程
 #1 通过ORM提交命令
 #2 翻译成SQL语句
 #3 调用ENGINE执行
 #3.1 获得连接
 #3.2 调用指定的DBAPI去执行SQL语句 ---> SQLAlchemy可执行纯的SQL语句: engine.execute('sql') 
''' # SQLAlchemy架构和操作流程

'''
建表:
 1. 创建模板
 from sqlalchemy.ext.declarative import declarative_base
 Base = declarative_base()
 
 2. 继承模板创建表
 Class myTable(Base)
 from sqlalchemy import Column
 数据格式有: Integer, Float, DECIMAL, String, Boolean, Date, DateTime
 表名: __tablename__ = ''
 约束有: ForeignKey(), ForeignKeyConstraint(), PrimaryKeyConstraint, UniqueConstraint(), Index()
 额外约束: __table_args__ = () 
 
 3. 创建连接engine
 from sqlalchemy import create_engine
 engine = create_engine(mysql + pymysql:// username:password@host:port/dbname)
 
 4. 调用engine建库
 Base.metadata.create_all(engine)
 # 删库
 Base.metadata.drop_all(engine) 
''' # 建表
from sqlalchemy.ext.declarative import declarative_base # 创建模板的函数
from sqlalchemy import Column,Integer,String,DATETIME # 数据类型
from sqlalchemy import ForeignKey,UniqueConstraint,Index
from sqlalchemy import create_engine # 创建引擎的函数

Base = declarative_base() # 1. 创建模板

# 创建单表 # 2. 继承模板创建表
class Business(Base):
 __tablename__ = 'business'
 id = Column(Integer, primary_key=True,autoincrement=True)
 bname = Column(String(32),nullable=False,index=True)

# 创建多对一
class Service(Base):
 __tablename__ = 'service'
 id = Column(Integer,primary_key=True,autoincrement=True)
 sname = Column(String(32),nullable=False,index=True)
 ip = Column(String(15),nullable=False)
 port = Column(Integer,nullable=False)

 business_id = Column(Integer,ForeignKey('business.id')) # 外键约束: 多对一

 __table_args = ( # 其他约束
 UniqueConstraint(ip,port,name='uix_ip_port'),
 Index('ix_id_sname',id,sname)
 )

# 创建一对一
class Role(Base):
 __tablename__ = 'role'
 id = Column(Integer,primary_key=True,autoincrement=True)
 rname = Column(String(32),nullable=False,index=True)
 priv = Column(String(64),nullable=False)

 business_id = Column(Integer,ForeignKey('business.id'),unique=True) # 外键约束: 一对一

class User(Base):
 __tablename__ = 'user'
 id = Column(Integer,primary_key=True,autoincrement=True)
 uname = Column(String(32),nullable=ForeignKey,index=True)

class User2Role(Base):
 __tablename__ = 'user2role'
 id = Column(Integer,primary_key=True,autoincrement=True)
 uid = Column(Integer,ForeignKey('user.id'))
 rid = Column(Integer,ForeignKey('role.id'))
 __table_args = (
 UniqueConstraint(uid,rid,name='uix_uid_rid')
 )

engine = create_engine('mysql+pymysql://root:[email protected]:3306/test2',max_overflow=5)

def init_db():
 Base.metadata.create_all(engine)

def drop_db():
 Base.metadata.drop_all(engine)

if __name__ == '__main__':
 init_db()

'''
操作: 
 1. 创建session
 from sqlalchemy.orm import sessionmaker
 Session = sessionmaker(bind=engine)
 session = Session()
 
 2. 增加
 row_obj = myTable(field=var)
 session.add(row_obj)
 session.add_all([
 myTable(field=var1),
 myTable(field=var2)
 ])
 session.commit() # 基于事务, 增删改必须提交
 
 3. 删除
 session.query(Dep).filter(Dep.id>3).delete()
 session.commit()
 
 4. 修改
 session.query(Dep).filter(Dep.id > 0).update({'dname':'哇哈哈'}) # 修改传入一个dict
 session.commit()
 
 
 5. 查询: 单表
 res = session.query(Dep).all() # 返回List, 每项为obj
 print(res[1].dname) # obj.attr 获得值
 
 from sqlalchemy import distinct
 res = session.query(distinct(Dep.dname)).all() # distinct 去重
 
 res = session.query(Dep.id,Dep.dname).all() # 查询指定field, 返回list,每项为tuple
 print(res)
 
 sql = session.query(Dep).filter(Dep.id >1, Dep.id<1000) # 条件查询, 返回sql语句对象
 print(sql.all()) # 返回List, 每项为obj
 
 sql = session.query(Emp).filter_by(ename='林海峰') # 条件查询只能传等于条件, 返回sql语句对象
 print(sql.first().ename)
 
 res = session.query(Emp).filter(Emp.id.between(1, 3)).all() # .bewteen(a,b)
 print(res)
 
 res = session.query(Emp).filter(Emp.id.in_([1, 3, 99, 101])).all() # .in_([1,2,3])
 print(res)
 
 res = session.query(Emp).filter(~Emp.id.in_([1, 3, 99, 101])) # not
 print(res)
 
 from sqlalchemy import and_, or_
 res = session.query(Emp).filter(and_(Emp.id > 0, Emp.ename == '林海峰')).all() # and
 res=session.query(Emp).filter(or_(Emp.id < 2,Emp.ename=='功夫熊猫')).all() # or
 
 res = session.query(Emp).filter(Emp.ename.like('%海_%')).all() # like('%_')
 
 res = session.query(Emp)[0:5:2] # limit [start:end:step]
 
 res = session.query(Emp).order_by(Emp.dep_id.desc(), Emp.id.asc()).all() # order_by(.desc(),.asc())
 
 from sqlalchemy.sql import func
 res = session.query(
 func.max(Emp.dep_id), # 聚合函数
 func.min(Emp.dep_id),
 func.sum(Emp.dep_id),
 func.avg(Emp.dep_id),
 func.count(Emp.dep_id),
 ).group_by(Emp.dep_id).all() # group_by() 
''' # 操作: 增删改, 单表查询

'''
多表查询:
 连接查询: 
 1. 内连接: 默认内连接, 自动关联foreign_key
 res=session.query(Emp.id,Emp.ename,Emp.dep_id,Dep.dname).join(Dep).all()
 
 2. 左连接: isouter = True
 res=session.query(Emp.id,Emp.ename,Emp.dep_id,Dep.dname).join(Dep,isouter=True).all()
 
 3. 右连接:同左连接,只是把两个表的位置换一下
 
 子查询:
 1. 子查询当做一张表, subquery()
 # select * from (select * from emp where id > 2);
 
 res = session.query(
 session.query(Emp).filter(Emp.id>8).subquery()
 ).all() 
 
 2. 子查询当做范围使用
 # select ename from emp where dep_id in (select id from dep where dname='销售');
 
 res = session.query(Emp.ename).filter(Emp.dep_id.in_(
 session.query(Dep.id).filter_by(dname='销售')
 )).all()
 
 3. 子查询当做select后的字段, as_scalar()
 # select ename as 员工姓名,(select dname from dep where id = emp.dep_id) as 部门名 from emp;
 
 sub_sql = session.query(Dep.name).filter(Dep.id==Emp.dep_id)
 res = session.query(Emp.ename,sub_sql.as_scalar()).all() 
 
 正反查询: 在含有外键的表中创建,relationship对象
 depart = relationship('Dep',backref='xxoo') # 'Dep'为类名不是表名, depart(用于正向查询), xxoo(用于反向查询) 且都不会创建字段
 # 正向查
 res = session.query(Emp).first()
 res.depart.dename # 获得'一表'中的值
 
 # 反向查
 res = session.query(Dep).first()
 res.xxoo # 返回一个List, 包含'多表'中关联的对象
''' # 操作: 多表查询