addCacheData method 
    
    
    
  Implementation
  Future<bool> addCacheData(APICacheDBModel model) async {
  await APICacheDBHelper.init();
  bool isSaved = false;
  model.syncTime = new DateTime.now().millisecondsSinceEpoch;
  int res;
  if (!await this.isAPICacheKeyExist(model.key)) {
    res = await APICacheDBHelper.insert(APICacheDBModel.table, model);
  } else {
    res = await APICacheDBHelper.customUpdate(
      APICacheDBModel.table,
      model,
      columnName: "key",
      columnValue: model.key,
    );
  }
  isSaved = res > 0 ? true : false;
  return isSaved;
}