private async connectMysql() {
    const access: ConnectionOptions = {
      host: process.env.HOST,
      user: process.env.USER,
      password: process.env.PASSWORD,
      database: process.env.DATABASE,
      multipleStatements: true,
      connectionLimit: 10,
      waitForConnections: true,
      typeCast: function (field, next) {
        if (field.type == "NEWDECIMAL") {
          var value = field.string();
          return value === null ? null : Number(value);
        }
        return next();
      },
    };
    this.con = mysql.createPool(access);
  }