python db类用法说明

import pymysql
 
class DB:
 __host = 'localhost' # 服务器地址
 __username = 'root' # 用户名
 __password = '' # 密码
 __database = 'test' # 数据库
 __field = '*' # 查询字段
 __where = '' # 条件
 __sql = False # 是否返回sql
 __join = '' # 联表
 __order = '' # 排序
 __limit = '' # 数量
 
 # 构造函数，在生成对象时调用
 def __init__(self, table):
  try:
   # 打开数据库连接 host, username, password, database
   self.db = pymysql.connect(self.__host, self.__username, self.__password, self.__database)
  except Exception as e:
   print(e)
   exit()
 
  # 使用 cursor() 方法创建一个游标对象 cursor
  self.cursor = self.db.cursor()
  self.table = table
 
 # 析构函数，释放对象时使用
 def __del__(self):
  try:
   # 关闭数据库连接
   self.db.close()
  except Exception as e:
   print(e)
 
 # 得到当前sql语句
 def getSql(self):
  self.__sql = True
  return self
 
 # 字段
 def field(self, str):
  self.__field = str
  return self
 
 # 联表
 def join(self, table, where):
  self.__join = ' LEFT JOIN ' + table + ' ON ' + where + ' '
  return self
 
 # 条件
 def where(self, param):
  self.__where = ' WHERE '
  if isinstance(param, list):
   for i in param:
    if isinstance(i[2], list):
     tmp = '('
     for j in i[2]:
      tmp += str(j) + ','
     tmp += ')'
     self.__where += '`' + i[0] + '` ' + i[1] + ' ' + tmp + ' AND '
    else:
     self.__where += '`' + i[0] + '` ' + i[1] + ' ' + str(i[2]) + ' AND '
   else:
    self.__where = self.__where[0:-4]
  else:
   self.__where += param
 
  return self
 
 # 排序
 def order(self, str):
  self.__order = ' ORDER BY ' + str
  return self
 
 # 数量
 def limit(self, str):
  self.__limit = ' LIMIT ' + str
  return self
 
 # 增加
 def insert(self, dict):
  key = value = ''
  for k, v in dict.items():
   key += '`' + k + '`,'
   value += '"' + v + '",'
 
  key = key[0:-1]
  value = value[0:-1]
 
  sql = 'INSERT INTO ' + self.table + ' (' + key + ') VALUES (' + value + ')'
  if self.__sql:
   return sql
 
  try:
   # 执行sql语句
   ret = self.cursor.execute(sql)
   # 提交到数据库执行
   self.db.commit()
   return ret
  except Exception as e:
   # 如果发生错误则回滚
   self.db.rollback()
   print(e)
   return 0
 
 # 删除
 def delete(self):
  if self.__where:
   sql = "DELETE FROM " + self.table + self.__where
   if self.__sql:
    return sql
 
   try:
    # 执行sql语句
    ret = self.cursor.execute(sql)
    # 提交到数据库执行
    self.db.commit()
    return ret
   except Exception as e:
    # 如果发生错误则回滚
    self.db.rollback()
    print(e)
    return 0
 
  else:
   raise BaseException('没有条件') # 抛异常
 
 # 修改
 def update(self, dict):
  str = ''
  for k, v in dict.items():
   str += '`' + k + '`="' + v + '",'
 
  str = str[0:-1]
  sql = 'UPDATE ' + self.table + ' SET ' + str
 
  if self.__where:
   sql += self.__where
  if self.__sql:
   return sql
 
  try:
   # 执行sql语句
   ret = self.cursor.execute(sql)
   # 提交到数据库执行
   self.db.commit()
   return ret
  except Exception as e:
   # 如果发生错误则回滚
   self.db.rollback()
   print(e)
   return 0
 
 # 查询
 def select(self):
  sql = "SELECT " + self.__field + " FROM " + self.table
 
  if self.__join:
   sql += self.__join
 
  if self.__where:
   sql += self.__where
 
  if self.__order:
   sql += self.__order
 
  if self.__limit:
   sql += self.__limit
 
  if self.__sql:
   return sql
 
  # 使用 execute() 方法执行 SQL 查询
  self.cursor.execute(sql)
 
  # 使用 fetchall() 方法获取所有数据.
  data = self.cursor.fetchall()
  return data
'''
DROP TABLE IF EXISTS `people`;
CREATE TABLE `people` (
 `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
 `name` varchar(20) CHARACTER SET utf8mb4 COLLATE utf8mb4_bin NOT NULL COMMENT '名字',
 `sex` varchar(7) DEFAULT '' COMMENT '性别',
 `job` varchar(6) DEFAULT '' COMMENT '工作',
 `age` varchar(6) DEFAULT '' COMMENT '年龄',
 `height` varchar(6) DEFAULT '' COMMENT '身高',
 `weight` varchar(6) DEFAULT '' COMMENT '体重',
 PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8;
INSERT INTO `people` VALUES ('1', '赵一', '男', '学生', '8', '120', '35');
INSERT INTO `people` VALUES ('2', '钱二', '女', '学生', '9', '111', '31');
INSERT INTO `people` VALUES ('3', '孙三', '男', '学生', '10', '123', '34');
INSERT INTO `people` VALUES ('4', '李四', '女', '学生', '11', '100', '30');
'''
db = DB('people')
 
# 增加
dict = {'name': '周五', 'sex': '男', 'job': '学生', 'age': '8', 'height': '121', 'weight': '32'}
data = db.insert(dict)
print(data)
 
# 删除
# data = db.where('id=6').delete()
# print(data)
 
# 修改
# dict = {'age': '9', 'height': '121', 'weight': '31'}
# data = db.where('id=7').update(dict)
# print(data)
 
# 查询 优化where条件 'id<11'
# data = db.field('id,name,age,job').where([['id', '>', 1]]).order('id desc').limit('3').select()
# print(data)