Flask-SQLAlchemy - 爱码网

SQLAlchemy

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。

1	`pip3 install sqlalchemy`

Flask-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://:@[:]/
 
pymysql

 mysql+pymysql://:@/[?]
 
MySQL-Connector

 mysql+mysqlconnector://:@[:]/
 
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()

#!/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()

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