/// <summary>
/// DB2实体集合构造函数，不设置ColumnName，每次全更新
/// </summary>
/// <param name="tableName">指定表名</param>
public DB2DataCatcher(string tableName, bool autoUpdate = false)
{
entities = new DB2Entities <T>("", tableName);
AutoUpdate = autoUpdate;
GetData();
}
/// <summary>
/// DB2实体集合构造函数
/// </summary>
/// <param name="columnName">设置时间列名，用于指定某列作为最后一条记录的依据</param>
/// <param name="tableName">指定表名</param>
public DB2DataCatcher(string columnName, string tableName)
{
entities = new DB2Entities <T>(columnName, tableName);
GetData();
}