EF中使用Linq的Lambda比较字符串格式日期大小

在使用EF时，想要比较字符串类型的日期时，参考以下：

SQL语句：
1）select *　from TableName where StartTime > ‘2015-04-08‘
2）select *　from TableName where StartTime >= ‘2015-04-08‘
3）select *　from TableName where StartTime < ‘2015-04-08‘
4）select *　from TableName where StartTime <= ‘2015-04-08‘

lambda表达式写法：
1）.Where(a => a.StartTime.CompareTo(‘2015-04-08‘) > 0)
2）.Where(a => a.StartTime.CompareTo(‘2015-04-08‘) >= 0)
3）.Where(a => a.StartTime.CompareTo(‘2015-04-08‘) < 0)
4）.Where(a => a.StartTime.CompareTo(‘2015-04-08‘) <= 0)

更规范的写法：
1）.Where(a => String.Compare(a.StartTime, ‘2015-04-08‘, StringComparison.Ordinal) > 0)
2）.Where(a => String.Compare(a.StartTime, ‘2015-04-08‘, StringComparison.Ordinal) >= 0)
3）.Where(a => String.Compare(a.StartTime, ‘2015-04-08‘, StringComparison.Ordinal) < 0)
4）.Where(a => String.Compare(a.StartTime, ‘2015-04-08‘, StringComparison.Ordinal) <= 0)