Python Flask SQLALchemy基础知识

一、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。

快速安装
pip3 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

二、使用　

1. 执行原生SQL语句

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）—— -1 永不回收
)

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()

#!/usr/bin/env python
# -*- coding:utf-8 -*-
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", max_overflow=0, pool_size=5)

def task(arg):
    conn = engine.contextual_connect()
    with conn:
        cur = conn.execute(
            "select * from t1"
        )
        result = cur.fetchall()
        print(result)

for i in range(20):
    t = threading.Thread(target=task, args=(i,))
    t.start()

#!/usr/bin/env python
# -*- coding:utf-8 -*-
import time
import threading
import sqlalchemy
from sqlalchemy import create_engine
from sqlalchemy.engine.base import Engine
from sqlalchemy.engine.result import ResultProxy
engine = create_engine("mysql+pymysql://root:123@127.0.0.1:3306/t1", max_overflow=0, pool_size=5)

def task(arg):
    cur = engine.execute("select * from t1")
    result = cur.fetchall()
    cur.close()
    print(result)

for i in range(20):
    t = threading.Thread(target=task, args=(i,))
    t.start()

注意: 查看连接 show status like 'Threads%';

2. ORM

a. 创建数据库表

 #!/usr/bin/env python
 # -*- coding:utf-8 -*-
 # Author:supery

 import datetime
 from sqlalchemy import create_engine
 from sqlalchemy.ext.declarative import declarative_base
 from sqlalchemy import Column, Integer, String, Text, ForeignKey, DateTime, UniqueConstraint, Index

 Base = declarative_base()

 class Users(Base):
     __tablename__ = 'users'

     id = Column(Integer, primary_key=True)          # 主键
     name = Column(String(32), index=True, nullable=False)   # 添加索引，不能为空
     email = Column(String(32), unique=True)
     ctime = Column(DateTime, default=datetime.datetime.now)
     # datetime.datetime.now不能加括号，加括号默认值就是第一次插入时间
     # extra = Column(Text, nullable=True)

     __table_args__ = (
         UniqueConstraint('id', 'name', name='uix_id_name'),    # 联合唯一索引
         Index('ix_id_name', 'name', 'email'),                   # 普通索引
     )
     _table_arhs__ = {
         'mysql_engine': 'InnoDb',                   # 设置表引擎
         'mysql_charset': 'utf8'                     # 设置表字符集
     }

 def init_db():
     """
     根据类创建数据库表
     :return:
     """
     engine = create_engine(
         "mysql+pymysql://root:123.com@10.0.0.10:3306/day123?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）——永不回收-1
     )

     Base.metadata.create_all(engine)

 def drop_db():
     """
     根据类删除数据库表
     :return:
     """
     engine = create_engine(
         "mysql+pymysql://root:123.com@10.0.0.10:3306/day123?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）——永不回收-1
     )

     Base.metadata.drop_all(engine)

 if __name__ == '__main__':
     # 初始化数据库，先删除再创建
     drop_db()
     init_db()

创建单表

 #!/usr/bin/env python
 # -*- coding:utf-8 -*-
 import datetime
 from sqlalchemy import create_engine
 from sqlalchemy.ext.declarative import declarative_base
 from sqlalchemy import Column, Integer, String, Text, ForeignKey, DateTime, UniqueConstraint, Index
 from sqlalchemy.orm import relationship

 Base = declarative_base()

 # ##################### 单表示例 #########################
 class Users(Base):
     __tablename__ = 'users'

     id = Column(Integer, primary_key=True)
     name = Column(String(32), index=True)
     age = Column(Integer, default=18)
     email = Column(String(32), unique=True)
     ctime = Column(DateTime, default=datetime.datetime.now)
     extra = Column(Text, nullable=True)

     __table_args__ = (
         # UniqueConstraint('id', 'name', name='uix_id_name'),
         # Index('ix_id_name', 'name', 'extra'),
     )

 class Hosts(Base):
     __tablename__ = 'hosts'

     id = Column(Integer, primary_key=True)
     name = Column(String(32), index=True)
     ctime = Column(DateTime, default=datetime.datetime.now)

 # ##################### 一对多示例 #########################
 class Hobby(Base):
     __tablename__ = 'hobby'
     id = Column(Integer, primary_key=True)
     caption = Column(String(50), default='篮球')

 class Person(Base):
     __tablename__ = 'person'
     nid = Column(Integer, primary_key=True)
     name = Column(String(32), index=True, nullable=True)
     hobby_id = Column(Integer, ForeignKey("hobby.id"))

     # 与生成表结构无关，仅用于查询方便
     hobby = relationship("Hobby", backref='pers')

 # ##################### 多对多示例 #########################

 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)

 def init_db():
     """
     根据类创建数据库表
     :return:
     """
     engine = create_engine(
         "mysql+pymysql://root:123@127.0.0.1:3306/s6?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）
     )

     Base.metadata.create_all(engine)

 def drop_db():
     """
     根据类删除数据库表
     :return:
     """
     engine = create_engine(
         "mysql+pymysql://root:123@127.0.0.1:3306/s6?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）
     )

     Base.metadata.drop_all(engine)

 if __name__ == '__main__':
     drop_db()
     init_db()

创建多个表(包含FK,M2M关系)

b. 操作数据库表

 #!/usr/bin/env python
 # -*- coding:utf- -*-
 from sqlalchemy.orm import sessionmaker
 from sqlalchemy import create_engine
 from models import Users

 engine = create_engine("mysql+pymysql://root:123@127.0.0.1:3306/s6", max_overflow=, pool_size=)
 Session = sessionmaker(bind=engine)

 # 每次执行数据库操作时，都需要创建一个session
 session = Session()

 # ############# 执行ORM操作 #############
 obj1 = Users(name="alex1")
 session.add(obj1)

 # 提交事务
 session.commit()
 # 关闭session
 session.close()

 #!/usr/bin/env python
 # -*- coding:utf-8 -*-
 import time
 import threading

 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
 from db import Users

 engine = create_engine("mysql+pymysql://root:123@127.0.0.1:3306/s6", max_overflow=0, pool_size=5)
 Session = sessionmaker(bind=engine)

 def task(arg):
     session = Session()

     obj1 = Users(name="alex1")
     session.add(obj1)

     session.commit()

 for i in range(10):
     t = threading.Thread(target=task, args=(i,))
     t.start()

多线程执行示例

 #!/usr/bin/env python
 # -*- coding:utf-8 -*-
 import time
 import threading

 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
 from sqlalchemy.sql import text

 from db import Users, Hosts

 engine = create_engine("mysql+pymysql://root:123@127.0.0.1:3306/s6", max_overflow=0, pool_size=5)
 Session = sessionmaker(bind=engine)

 session = Session()

 # ################ 添加 ################
 """
 obj1 = Users(name="wupeiqi")
 session.add(obj1)

 session.add_all([
     Users(name="wupeiqi"),
     Users(name="alex"),
     Hosts(name="c1.com"),
 ])
 session.commit()
 """

 # ################ 删除 ################
 """
 session.query(Users).filter(Users.id > 2).delete()
 session.commit()
 """
 # ################ 修改 ################
 """
 session.query(Users).filter(Users.id > 0).update({"name" : "099"})
 session.query(Users).filter(Users.id > 0).update({Users.name: Users.name + "099"}, synchronize_session=False)
 session.query(Users).filter(Users.id > 0).update({"age": Users.age + 1}, synchronize_session="evaluate")
 session.commit()
 """
 # ################ 查询 ################
 """
 r1 = session.query(Users).all()
 r2 = session.query(Users.name.label('xx'), Users.age).all()
 r3 = session.query(Users).filter(Users.name == "alex").all()
 r4 = session.query(Users).filter_by(name='alex').all()
 r5 = session.query(Users).filter_by(name='alex').first()
 r6 = session.query(Users).filter(text("id<:value and name=:name")).params(value=224, name='fred').order_by(Users.id).all()
 r7 = session.query(Users).from_statement(text("SELECT * FROM users where name=:name")).params(name='ed').all()
 """

 session.close()

基本的增删改查操作

 #　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
 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.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()

 # 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()

 # 组合
 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()

常用操作

 #!/usr/bin/env python
 # -*- coding:utf-8 -*-
 import time
 import threading

 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
 from sqlalchemy.sql import text
 from sqlalchemy.engine.result import ResultProxy
 from db import Users, Hosts

 engine = create_engine("mysql+pymysql://root:123@127.0.0.1:3306/s6", max_overflow=0, pool_size=5)
 Session = sessionmaker(bind=engine)

 session = Session()

 # 查询
 # cursor = session.execute('select * from users')
 # result = cursor.fetchall()

 # 添加
 cursor = session.execute('insert into users(name) values(:value)',params={"value":'wupeiqi'})
 session.commit()
 print(cursor.lastrowid)

 session.close()

原生SQL语句

 #!/usr/bin/env python
 # -*- coding:utf-8 -*-
 import time
 import threading

 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
 from sqlalchemy.sql import text
 from sqlalchemy.engine.result import ResultProxy
 from db import Users, Hosts, Hobby, Person

 engine = create_engine("mysql+pymysql://root:123@127.0.0.1:3306/s6?charset=utf8", max_overflow=0, pool_size=5)
 Session = sessionmaker(bind=engine)
 session = Session()
 # 添加
 """
 session.add_all([
     Hobby(caption='乒乓球'),
     Hobby(caption='羽毛球'),
     Person(name='张三', hobby_id=3),
     Person(name='李四', hobby_id=4),
 ])

 person = Person(name='张九', hobby=Hobby(caption='姑娘'))
 session.add(person)

 hb = Hobby(caption='人妖')
 hb.pers = [Person(name='文飞'), Person(name='博雅')]
 session.add(hb)

 session.commit()
 """

 # 使用relationship正向查询
 """
 v = session.query(Person).first()
 print(v.name)
 print(v.hobby.caption)
 """

 # 使用relationship反向查询
 """
 v = session.query(Hobby).first()
 print(v.caption)
 print(v.pers)
 """

 session.close()

基于relationship操作ForeignKey

 #!/usr/bin/env python
 # -*- coding:utf-8 -*-
 import time
 import threading

 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
 from sqlalchemy.sql import text
 from sqlalchemy.engine.result import ResultProxy
 from db import Users, Hosts, Hobby, Person, Group, Server, Server2Group

 engine = create_engine("mysql+pymysql://root:123@127.0.0.1:3306/s6?charset=utf8", max_overflow=0, pool_size=5)
 Session = sessionmaker(bind=engine)
 session = Session()
 # 添加
 """
 session.add_all([
     Server(hostname='c1.com'),
     Server(hostname='c2.com'),
     Group(name='A组'),
     Group(name='B组'),
 ])
 session.commit()

 s2g = Server2Group(server_id=1, group_id=1)
 session.add(s2g)
 session.commit()

 gp = Group(name='C组')
 gp.servers = [Server(hostname='c3.com'),Server(hostname='c4.com')]
 session.add(gp)
 session.commit()

 ser = Server(hostname='c6.com')
 ser.groups = [Group(name='F组'),Group(name='G组')]
 session.add(ser)
 session.commit()
 """

 # 使用relationship正向查询
 """
 v = session.query(Group).first()
 print(v.name)
 print(v.servers)
 """

 # 使用relationship反向查询
 """
 v = session.query(Server).first()
 print(v.hostname)
 print(v.groups)
 """

 session.close()

基于relationship操作m2m

 #!/usr/bin/env python
 # -*- coding:utf-8 -*-
 import time
 import threading

 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
 from sqlalchemy.sql import text, func
 from sqlalchemy.engine.result import ResultProxy
 from db import Users, Hosts, Hobby, Person, Group, Server, Server2Group

 engine = create_engine("mysql+pymysql://root:123@127.0.0.1:3306/s6?charset=utf8", max_overflow=0, pool_size=5)
 Session = sessionmaker(bind=engine)
 session = Session()

 # 关联子查询
 subqry = session.query(func.count(Server.id).label("sid")).filter(Server.id == Group.id).correlate(Group).as_scalar()
 result = session.query(Group.name, subqry)
 """
 SELECT `group`.name AS group_name, (SELECT count(server.id) AS sid
 FROM server
 WHERE server.id = `group`.id) AS anon_1
 FROM `group`
 """

 # 原生SQL
 """
 # 查询
 cursor = session.execute('select * from users')
 result = cursor.fetchall()

 # 添加
 cursor = session.execute('insert into users(name) values(:value)',params={"value":'wupeiqi'})
 session.commit()
 print(cursor.lastrowid)
 """

 session.close()

其他

PS：注意
1. 默认不能修改表的字段,如果修改需要用的到sqlalchemy的一个组件进行修改字段
2. pool_recycle=-1 永远不回收
3. ctime = Column(DateTime, default=datetime.datetime.now)
    datetime.datetime.now不能加括号，加括号默认值就是第一次插入时间