Flask - SQLAlchemy
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一、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。
1.安装
pip3 install sqlalchemy
2.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）
)
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()
1 #!/usr/bin/env python 2 # -*- coding:utf-8 -*- 3 import time 4 import threading 5 import sqlalchemy 6 from sqlalchemy import create_engine 7 from sqlalchemy.engine.base import Engine 8 9 engine = create_engine("mysql+pymysql://root:123@127.0.0.1:3306/t1", max_overflow=0, pool_size=5) 10 11 12 def task(arg): 13 conn = engine.contextual_connect() 14 with conn: 15 cur = conn.execute( 16 "select * from t1" 17 ) 18 result = cur.fetchall() 19 print(result) 20 21 22 for i in range(20): 23 t = threading.Thread(target=task, args=(i,)) 24 t.start()
1 #!/usr/bin/env python 2 # -*- coding:utf-8 -*- 3 import time 4 import threading 5 import sqlalchemy 6 from sqlalchemy import create_engine 7 from sqlalchemy.engine.base import Engine 8 from sqlalchemy.engine.result import ResultProxy 9 engine = create_engine("mysql+pymysql://root:123@127.0.0.1:3306/t1", max_overflow=0, pool_size=5) 10 11 12 def task(arg): 13 cur = engine.execute("select * from t1") 14 result = cur.fetchall() 15 cur.close() 16 print(result) 17 18 19 for i in range(20): 20 t = threading.Thread(target=task, args=(i,)) 21 t.start()
注意: 查看连接 show status like \'Threads%\';
2. ORM
a. 创建数据库表
1 #!/usr/bin/env python 2 # -*- coding:utf-8 -*- 3 import datetime 4 from sqlalchemy import create_engine 5 from sqlalchemy.ext.declarative import declarative_base 6 from sqlalchemy import Column, Integer, String, Text, ForeignKey, DateTime, UniqueConstraint, Index 7 8 Base = declarative_base() 9 10 11 class Users(Base): 12 __tablename__ = \'users\' 13 14 id = Column(Integer, primary_key=True) 15 name = Column(String(32), index=True, nullable=False) 16 # email = Column(String(32), unique=True) 17 # ctime = Column(DateTime, default=datetime.datetime.now) 18 # extra = Column(Text, nullable=True) 19 20 __table_args__ = ( 21 # UniqueConstraint(\'id\', \'name\', name=\'uix_id_name\'), 22 # Index(\'ix_id_name\', \'name\', \'email\'), 23 ) 24 25 26 def init_db(): 27 """ 28 根据类创建数据库表 29 :return: 30 """ 31 engine = create_engine( 32 "mysql+pymysql://root:123@127.0.0.1:3306/s6?charset=utf8", 33 max_overflow=0, # 超过连接池大小外最多创建的连接 34 pool_size=5, # 连接池大小 35 pool_timeout=30, # 池中没有线程最多等待的时间，否则报错 36 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） 37 ) 38 39 Base.metadata.create_all(engine) 40 41 42 def drop_db(): 43 """ 44 根据类删除数据库表 45 :return: 46 """ 47 engine = create_engine( 48 "mysql+pymysql://root:123@127.0.0.1:3306/s6?charset=utf8", 49 max_overflow=0, # 超过连接池大小外最多创建的连接 50 pool_size=5, # 连接池大小 51 pool_timeout=30, # 池中没有线程最多等待的时间，否则报错 52 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） 53 ) 54 55 Base.metadata.drop_all(engine) 56 57 58 if __name__ == \'__main__\': 59 drop_db() 60 init_db() 61 62 创建单表
1 #!/usr/bin/env python 2 # -*- coding:utf-8 -*- 3 import datetime 4 from sqlalchemy import create_engine 5 from sqlalchemy.ext.declarative import declarative_base 6 from sqlalchemy import Column, Integer, String, Text, ForeignKey, DateTime, UniqueConstraint, Index 7 from sqlalchemy.orm import relationship 8 9 Base = declarative_base() 10 11 12 # ##################### 单表示例 ######################### 13 class Users(Base): 14 __tablename__ = \'users\' 15 16 id = Column(Integer, primary_key=True) 17 name = Column(String(32), index=True) 18 age = Column(Integer, default=18) 19 email = Column(String(32), unique=True) 20 ctime = Column(DateTime, default=datetime.datetime.now) 21 extra = Column(Text, nullable=True) 22 23 __table_args__ = ( 24 # UniqueConstraint(\'id\', \'name\', name=\'uix_id_name\'), 25 # Index(\'ix_id_name\', \'name\', \'extra\'), 26 ) 27 28 29 class Hosts(Base): 30 __tablename__ = \'hosts\' 31 32 id = Column(Integer, primary_key=True) 33 name = Column(String(32), index=True) 34 ctime = Column(DateTime, default=datetime.datetime.now) 35 36 37 # ##################### 一对多示例 ######################### 38 class Hobby(Base): 39 __tablename__ = \'hobby\' 40 id = Column(Integer, primary_key=True) 41 caption = Column(String(50), default=\'篮球\') 42 43 44 class Person(Base): 45 __tablename__ = \'person\' 46 nid = Column(Integer, primary_key=True) 47 name = Column(String(32), index=True, nullable=True) 48 hobby_id = Column(Integer, ForeignKey("hobby.id")) 49 50 # 与生成表结构无关，仅用于查询方便 51 hobby = relationship("Hobby", backref=\'pers\') 52 53 54 # ##################### 多对多示例 ######################### 55 56 class Server2Group(Base): 57 __tablename__ = \'server2group\' 58 id = Column(Integer, primary_key=True, autoincrement=True) 59 server_id = Column(Integer, ForeignKey(\'server.id\')) 60 group_id = Column(Integer, ForeignKey(\'group.id\')) 61 62 63 class Group(Base): 64 __tablename__ = \'group\' 65 id = Column(Integer, primary_key=True) 66 name = Column(String(64), unique=True, nullable=False) 67 68 # 与生成表结构无关，仅用于查询方便 69 servers = relationship(\'Server\', secondary=\'server2group\', backref=\'groups\') 70 71 72 class Server(Base): 73 __tablename__ = \'server\' 74 75 id = Column(Integer, primary_key=True, autoincrement=True) 76 hostname = Column(String(64), unique=True, nullable=False) 77 78 79 def init_db(): 80 """ 81 根据类创建数据库表 82 :return: 83 """ 84 engine = create_engine( 85 "mysql+pymysql://root:123@127.0.0.1:3306/s6?charset=utf8", 86 max_overflow=0, # 超过连接池大小外最多创建的连接 87 pool_size=5, # 连接池大小 88 pool_timeout=30, # 池中没有线程最多等待的时间，否则报错 89 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） 90 ) 91 92 Base.metadata.create_all(engine) 93 94 95 def drop_db(): 96 """ 97 根据类删除数据库表 98 :return: 99 """ 100 engine = create_engine( 101 "mysql+pymysql://root:123@127.0.0.1:3306/s6?charset=utf8", 102 max_overflow=0, # 超过连接池大小外最多创建的连接 103 pool_size=5, # 连接池大小 104 pool_timeout=30, # 池中没有线程最多等待的时间，否则报错 105 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） 106 ) 107 108 Base.metadata.drop_all(engine) 109 110 111 if __name__ == \'__main__\': 112 drop_db() 113 init_db() 114 115 创建多个表并包含Fk、M2M关系
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()
3.基于scoped_session实现线程安全
1 #!/usr/bin/env python 2 # -*- coding:utf-8 -*- 3 from sqlalchemy.orm import sessionmaker 4 from sqlalchemy import create_engine 5 from sqlalchemy.orm import scoped_session 6 from models import Users 7 8 engine = create_engine("mysql+pymysql://root:123@127.0.0.1:3306/s6", max_overflow=0, pool_size=5) 9 Session = sessionmaker(bind=engine) 10 11 """ 12 # 线程安全，基于本地线程实现每个线程用同一个session 13 # 特殊的：scoped_session中有原来方法的Session中的一下方法： 14 15 public_methods = ( 16 \'__contains__\', \'__iter__\', \'add\', \'add_all\', \'begin\', \'begin_nested\', 17 \'close\', \'commit\', \'connection\', \'delete\', \'execute\', \'expire\', 18 \'expire_all\', \'expunge\', \'expunge_all\', \'flush\', \'get_bind\', 19 \'is_modified\', \'bulk_save_objects\', \'bulk_insert_mappings\', 20 \'bulk_update_mappings\', 21 \'merge\', \'query\', \'refresh\', \'rollback\', 22 \'scalar\' 23 ) 24 """ 25 session = scoped_session(Session) 26 27 28 # ############# 执行ORM操作 ############# 29 obj1 = Users(name="alex1") 30 session.add(obj1) 31 32 33 34 # 提交事务 35 session.commit() 36 # 关闭session 37 session.close() 38 39 基于scoped_session实现线程安全
4.多线程执行示例
1 #!/usr/bin/env python 2 # -*- coding:utf-8 -*- 3 import time 4 import threading 5 6 from sqlalchemy.ext.declarative import declarative_base 7 from sqlalchemy import Column, Integer, String, ForeignKey, UniqueConstraint, Index 8 from sqlalchemy.orm import sessionmaker, relationship 9 from sqlalchemy import create_engine 10 from db import Users 11 12 engine = create_engine("mysql+pymysql://root:123@127.0.0.1:3306/s6", max_overflow=0, pool_size=5) 13 Session = sessionmaker(bind=engine) 14 15 16 def task(arg): 17 session = Session() 18 19 obj1 = Users(name="alex1") 20 session.add(obj1) 21 22 session.commit() 23 24 25 for i in range(10): 26 t = threading.Thread(target=task, args=(i,)) 27 t.start() 28 29 多线程执行示例
5.基本增删改查示例
1 #!/usr/bin/env python 2 # -*- coding:utf-8 -*- 3 import time 4 import threading 5 6 from sqlalchemy.ext.declarative import declarative_base 7 from sqlalchemy import Column, Integer, String, ForeignKey, UniqueConstraint, Index 8 from sqlalchemy.orm import sessionmaker, relationship 9 from sqlalchemy import create_engine 10 from sqlalchemy.sql import text 11 12 from db import Users, Hosts 13 14 engine = create_engine("mysql+pymysql://root:123@127.0.0.1:3306/s6", max_overflow=0, pool_size=5) 15 Session = sessionmaker(bind=engine) 16 17 session = Session() 18 19 # ################ 添加 ################ 20 """ 21 obj1 = Users(name="wupeiqi") 22 session.add(obj1) 23 24 session.add_all([ 25 Users(name="wupeiqi"), 26 Users(name="alex"), 27 Hosts(name="c1.com"), 28 ]) 29 session.commit() 30 """ 31 32 # ################ 删除 ################ 33 """ 34 session.query(Users).filter(Users.id > 2).delete() 35 session.commit() 36 """ 37 # ################ 修改 ################ 38 """ 39 session.query(Users).filter(Users.id > 0).update({"name" : "099"}) 40 session.query(Users).filter(Users.id > 0).update({Users.name: Users.name + "099"}, synchronize_session=False) 41 session.query(Users).filter(Users.id > 0).update({"age": Users.age + 1}, synchronize_session="evaluate") 42 session.commit() 43 """ 44 # ################ 查询 ################ 45 """ 46 r1 = session.query(Users).all() 47 r2 = session.query(Users.name.label(\'xx\'), Users.age).all() 48 r3 = session.query(Users).filter(Users.name == "alex").all() 49 r4 = session.query(Users).filter_by(name=\'alex\').all() 50 r5 = session.query(Users).filter_by(name=\'alex\').first() 51 r6 = session.query(Users).filter(text("id<:value and name=:name")).params(value=224, name=\'fred\').order_by(Users.id).all() 52 r7 = session.query(Users).from_statement(text("SELECT * FROM users where name=:name")).params(name=\'ed\').all() 53 """ 54 55 56 session.close() 57 58 基本增删改查示例
6.常用操作
1 1. 指定列 2 flask_sqlalchemy 调用存储过程Flask 学习-13.Flask-SQLAlchemy 新建模型和字段
深入浅出Flask(47)：flask_sqlalchemy的应用动态绑定