Python MySQL 数据库

python DB API

• python访问数据库的统一接口规范,完成不同数据库的访问
• 包含的内容: connection cursor exceptions

• 访问数据库流程: 1.创建connection 2.获取cursor 3.操作 4.关闭cursor 5.关闭connection

  python MySQL开发环境

  

  连接对象connection

• 连接对象: python客户端与数据库的网络连接
• 创建方法: pymysql.connect(参数)
  
• connection对象支持的方法:
  
• 例子:

import pymysql

conn = pymysql.connect(
    host = '127.0.0.1',
    port = 3306,
    user = 'root',
    db = 'database1',
    charset = 'utf-8')
cursor = conn.cursor()

print(conn)
print(cursor)

cursor.close()
conn.close()

游标对象cursor

• 游标对象: 用于执行查询和获取结果
• cursor对象支持的方法:
  
• execute()方法: 执行SQL,将结果从数据库获取到客户端
  

• fetch*()方法: 移动rownumber,返回数据
  

  实例 - select查询数据

• 流程
  
• 代码

import pymysql

conn = pymysql.connect(
    host = '127.0.0.1',
    port = 3306,
    user = 'root',
    db = 'database1',
    charset = 'utf-8'
)
cursor = conn.cursor()

sql = "select * from table"
cursor.execute(sql)

print(cursor.rowcount)

rs = cursor.fetchone()
print(rs)

rs = cursor.fetchmany(3)
print(rs)

rs = cursor.fetchall()
print(rs)

cursor.close()
conn.close()

实例 - insert/update/delete更新数据

• 流程
  
• 事务: 访问和更新数据库的一个程序执行单元
  
• 开发中怎样使用事务
  1.关闭自动commit: 设置conn.autocommit(False),默认就是这个状态
  2.正常结束事务: conn.commit()
  3.异常结束任务: conn.rollback()
• 代码

import pymysql

conn = pymysql.connect(
    host = '127.0.0.1',
    port = 3306,
    user = 'root',
    db = 'database1',
    charset = 'utf-8'
)
cursor = conn.cursor()

sql_insert = "insert into database1(userid,username) values(10,'name10')"
sql_update = "update database1 set username='name91' where userid = 9"
sql_delete = "delete from database1 where userid < 3"

try:
    cursor.execute(sql_insert)
    print(cursor.rowcount) # 查看对多少行造成了影响
    cursor.execute(sql_update)
    print(cursor.rowcount)
    cursor.execute(sql_delete)
    print(cursor.rowcount)
    conn.commit() #提交,更新数据库
exception Exception as e:
    print e
    conn.rollback() #回滚,只要有一条有错就啥都不提交了

cursor.close()
conn.close()

银行转账实例 - A给B转账100元

• 流程
  
• 实例数据库
• 代码

# coding:utf8
import pymysql
import sys

class TransferMoney(object):
    def __init__(self,conn):
        self.conn = conn

    def check_acct_available(self,acctid):
        cursor = self.conn.cursor()
        try:
            sql = "select * from account where acctid=%s" % acctid
            cursor.execute(sql)
            print("check_acct_available:"+sql)
            rs = cursor.fetchall()
            if len(rs)!=1:
                raise Exception("账号%s不存在" % acctid)
        finally:
            cursor.close()

    def has_enough_money(self,acctid, money):
        cursor = self.conn.cursor()
        try:
            sql = "select * from account where acctid=%s and money>%s" % (acctid,money)
            cursor.execute(sql)
            print("has_enough_money:" + sql)
            rs = cursor.fetchall()
            if len(rs) != 1:
                raise Exception("账号%s没有足够的钱" % acctid)
        finally:
            cursor.close()

    def reduce_money(self,acctid):
        cursor = self.conn.cursor()
        try:
            sql = "update account set money=money-%s where acctid=%s" % (money,acctid)
            cursor.execute(sql)
            print("reduce_money:" + sql)
            rs = cursor.fetchall()
            if cursor.rowcount != 1:
                raise Exception("账号%s减款失败" % acctid)
        finally:
            cursor.close()

    def add_money(self,acctid):
        cursor = self.conn.cursor()
        try:
            sql = "update account set money=money+%s where acctid=%s" % (money, acctid)
            cursor.execute(sql)
            print("reduce_money:" + sql)
            rs = cursor.fetchall()
            if cursor.rowcount != 1:
                raise Exception("账号%s加款失败" % acctid)
        finally:
            cursor.close()

    def transfer(self,source_acctid,target_acctid,money):
        try:
            self.check_acct_available(source_acctid)
            self.check_acct_available(target_acctid)
            self.has_enough_money(source_acctid,money)
            self.reduce_money(source_acctid)
            self.add_money(target_acctid)
            self.conn.commit()
        except Exception as e:
            self.conn.rollback()
            raise e

if __name__ == "__main__":
    source_acctid = sys.argv[1]
    target_acctid = sys.argv[2]
    money = sys.argv[3]

    conn = pymysql.connect(host='127.0.0.1',user='root',
                passwd='123456',port=3306,db='database1')
    tr_money = TransferMoney(conn)

    try:
        tr_money.transfer(source_acctid,target_acctid,money)
    except Exception as e:
        print("出现问题:"+str(e))
    finally:
        conn.close()