Python學習筆記 - PostgreSQL的使用

一、安裝PostgreSQL模塊

pip install psycopg2

有時候會失敗，多安裝2次就好了(我是第二次成功了)。

二、數據庫連接接口

由於Python統一了數據庫連接的接口，所以psycopg2和 MySQLdb 在使用方式上是類似的：

pymysql.Connect()參數說明
host(str):      MySQL服務器地址
port(int):      MySQL服務器端口號
user(str):      用戶名
password(str):  密碼
database(str):  數據庫名稱

connection對象支持的方法
cursor()        使用該連接創建並返回游標
commit()        提交當前事務
rollback()      回滾當前事務
close()         關閉連接

cursor對象支持的方法
execute(op)     執行一個數據庫的查詢命令
fetchone()      取得結果集的下一行
fetchmany(size) 獲取結果集的下幾行
fetchall()      獲取結果集中的所有行
rowcount()      返回數據條數或影響行數
close()         關閉游標對象

 

三、范例

MySql腳本

-- ----------------------------
-- Table structure for account
-- ----------------------------
DROP TABLE IF EXISTS `account`;
CREATE TABLE `account`  (
  `acctid` varchar(50) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL,
  `name` varchar(50) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL,
  `money` decimal(50, 0) NULL DEFAULT NULL
) ENGINE = InnoDB CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Dynamic;

-- ----------------------------
-- Records of account
-- ----------------------------
INSERT INTO `account` VALUES ('1', '張三', 50);
INSERT INTO `account` VALUES ('2', '李四', 150);

 

Python程序

#   coding:utf8
import sys
import psycopg2 #PostgreSQL

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
            print("check_acct_available:" + sql)
            cursor.execute(sql)
            rs = cursor.fetchall()
            if len(rs) != 1:
                raise Exception("帳號%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)
            print("has_enough_money:" + sql)
            cursor.execute(sql)
            rs = cursor.fetchall()
            if len(rs) != 1:
                raise Exception("帳號%s沒有足夠的金額" % acctid)
        finally:
            cursor.close()

    def reduce_money(self, acctid, money):
        cursor = self.conn.cursor()
        try:
            sql = "update account set money=money-%s where acctid='%s' " % (
                money, acctid)
            print("reduce_money:" + sql)
            cursor.execute(sql)
            if cursor.rowcount != 1:
                raise Exception("帳號%s減款失敗" % acctid)
        finally:
            cursor.close()

    def add_money(self, acctid, money):
        cursor = self.conn.cursor()
        try:
            sql = "update account set money=money+%s where acctid='%s' " % (
                money, acctid)
            print("add_money:" + sql)
            cursor.execute(sql)
            if cursor.rowcount != 1:
                raise Exception("帳號%s加款失敗" % 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, money)
            self.add_money(target_acctid, money)
            self.conn.commit()
        except Exception as e:
            self.conn.rollback()
            print("transfer出現異常：" + str(e))
            raise e


def main():
    source_acctid = sys.argv[1]
    print("轉出帳號=" + source_acctid)
    target_acctid = sys.argv[2]
    print("轉入帳號=" + target_acctid)
    money = sys.argv[3]
    print("金額=" + money)

    # 連接數據庫 MySql
    #conn = pymysql.Connect(
    #    host='localhost',
    #    port=3306,
    #    user='root',
    #    passwd='root',
    #    db='OtkDb',
    #    charset='utf8')

　　　 # 連接數據庫PostgreSQL

　　　　conn = psycopg2.connect(

　　　　　　host='localhost',

　　　　　　port=5432,

　　　　　　user='postgres',

　　　　　　password='postgres',

　　　　　　database='OtkDb')

    tr_money = TransferMoney(conn)

    try:
        tr_money.transfer(source_acctid, target_acctid, money)
    except Exception as e:
        print("main出現異常：" + str(e))
    finally:
        conn.close()


if __name__ == '__main__':
    main()

 四、運行效果

PS H:\web\Python> & python h:\web\Python\01.MySql\db.py 1 2 50
轉出帳號=1
轉入帳號=2
金額=50
check_acct_available:select * from account where acctid='1'
check_acct_available:select * from account where acctid='2'
has_enough_money:select * from account where acctid='1' and money>50
reduce_money:update account set money=money-50 where acctid='1'
add_money:update account set money=money+50 where acctid='2'


PS H:\web\Python> & python h:\web\Python\01.MySql\db.py 1 2 50
轉出帳號=1
轉入帳號=2
金額=50
check_acct_available:select * from account where acctid='1'
check_acct_available:select * from account where acctid='2'
has_enough_money:select * from account where acctid='1' and money>50
transfer出現異常：帳號1沒有足夠的金額
main出現異常：帳號1沒有足夠的金額

 

參考：

https://www.cnblogs.com/Erick-L/p/7106816.html