Python Day45

SQLAlchemy

SQLAlchemy是Python编程语言下的一款ORM框架，该框架建立在数据库APL之上，使用关系对象映射进行数据库操作，简言之便是：将对象转换成SQL，然后使用数据执行SQL并获取执行结果

安装：

pip3 install  SQLAlchemy

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...]

ORM功能使用：

使用ORM/Schema Type/SQL Expression

Language/Engine/ConnectionPooling/Dialect所有组件对数据进行操作。根据类创建对象，对象转换成SQL，执行SQL。

1创建表

from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String, ForeignKey, UniqueConstraint, Index
from sqlalchemy.orm import sessionmaker, relationship
from sqlalchemy import create_engine

engine = create_engine("mysql+pymysql://root:123@127.0.0.1:3306/t1", max_overflow=5)

Base = declarative_base()

创建单表

class users(Base):
        __tablename__='users'
        id = Column(Integer,primary_key=True)
        name = Column(VARCHAR(32))
        extra = Column(VARCHAR(32))
         __table_args__ = (
    UniqueConstraint('id', 'name', name='uix_id_name'),
        Index('ix_id_name', 'name', 'extra'),
    )

一对多

class Favor(Base):
    __tablename__ = 'favor'
    nid = Column(Integer, primary_key=True)
    caption = Column(VARCHAR(50), default='red', unique=True)
 
 
class Person(Base):
    __tablename__ = 'person'
    nid = Column(Integer, primary_key=True)
    name = Column(VARCHAR(32), index=True, nullable=True)
    favor_id = Column(Integer, ForeignKey("favor.nid"))
 

多对多

class Group(Base):
    __tablename__ = 'group'
    id = Column(Integer, primary_key=True)
    name = Column(VARCHAR(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(VARCHAR(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)

增加

## 增加一条数据
obj = Users(name="alex0", extra='sb')
session.add(obj)

## 增加多条数据
session.add_all([
Users(name="alex1", extra='sb'),
Users(name="alex2", extra='sb'),
])

session.commit()

修改

session.query(Users).filter(Users.id > 2).update({"name" : "099"})
session.commit()

查询

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()

高级查询：

#　条件
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()

# 通配符
ret = session.query(Users).filter(Users.name.like('e%')).all()
ret = session.query(Users).filter(~Users.name.like('e%')).all()

# 限制 limit
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()

# 分组
from sqlalchemy.sql import func

ret = session.query(Users).group_by(Users.extra).all()
ret = session.query(
func.max(Users.id),
func.min(Users.id)).group_by(Users.name).all()

ret = session.query(
func.max(Users.id),
func.min(Users.id)).group_by(Users.name).having(func.min(Users.id) >2).all()

# 连表

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()

原文地址：https://www.cnblogs.com/xinfan1/p/11045267.html