python 全栈开发，Day141(flask之应用上下文,SQLAlchemy)

 

一、flask之应用上下文

由于时间关系，详细过程略...

草稿图

 

 

参考链接：

http://www.cnblogs.com/zhaopanpan/p/9457343.html

 

总结：

上下文管理（应用上下文）
关键点
请求上线文:
ctx = RequestContext(request/session)
应用上下文:
app_ctx = AppContext(app/g)

问：flask中g的作用？一次请求周期中保存一个公用值。

g应用示例：
from flask import Flask,request,session,g,current_app

app = Flask(__name__)

@app.before_request
def b1():
g.x1 = 123

@app.route('/index')
def index():
print(g.x1)

if __name__ == '__main__':
app.run()

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二、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。

pip3 install sqlalchemy

流程图

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语句

举例1

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()

View Code

 

举例2

#!/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()

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举例3

#!/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()

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注意: 查看连接 show status like 'Threads%';

 

2. ORM

a. 创建数据库表

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

Base = declarative_base()

class Users(Base):
__tablename__ = 'users'

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)
# extra = Column(Text, nullable=True)

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

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()

创建单表

View Code

 

创建多个表并包含Fk、M2M关系

#!/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()

创建多个表并包含Fk、M2M关系

View Code

指定关联列：hobby = relationship("Hobby", backref='pers',foreign_keys="Person.hobby_id")

 

b. 操作数据库表

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

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基于scoped_session实现线程安全

#!/usr/bin/env python
# -*- coding:utf-8 -*-
from sqlalchemy.orm import sessionmaker
from sqlalchemy import create_engine
from sqlalchemy.orm import scoped_session
from models 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)

"""
# 线程安全，基于本地线程实现每个线程用同一个session
# 特殊的：scoped_session中有原来方法的Session中的一下方法：

public_methods = (
'__contains__', '__iter__', 'add', 'add_all', 'begin', 'begin_nested',
'close', 'commit', 'connection', 'delete', 'execute', 'expire',
'expire_all', 'expunge', 'expunge_all', 'flush', 'get_bind',
'is_modified', 'bulk_save_objects', 'bulk_insert_mappings',
'bulk_update_mappings',
'merge', 'query', 'refresh', 'rollback',
'scalar'
)
"""
session = scoped_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()

基于scoped_session实现线程安全

View Code

 

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 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

View Code

 

基本增删改查示例

#!/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()

基本增删改查示例

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常用操作

#　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

View Code

 

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

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

View Code

 

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

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

View Code

 

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
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

View Code

 

其他

#!/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

View Code

 

 

由于时间关系，详细过程略...

 

本文参考链接：

https://www.cnblogs.com/wupeiqi/articles/8259356.html

 

未完待续...

 

posted @ 2018-10-11 20:19 肖祥 阅读(...) 评论(...) 编辑 收藏