/// <summary>
/// 返回序列的唯一元素；如果该序列并非恰好包含一个元素，则会引发异常。
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="queryable"></param>
/// <returns></returns>
public static T Single <T>(this Queryable <T> queryable)
{
if (queryable.OrderBy.IsNullOrEmpty())
{
queryable.OrderBy = "GETDATE()";
}
queryable.Skip(0);
queryable.Take(1);
return(queryable.ToList().Single());
}
/// <summary>
/// 返回序列中的第一个元素。
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="queryable"></param>
/// <returns></returns>
public static T First <T>(this Queryable <T> queryable)
{
if (queryable.OrderBy.IsNullOrEmpty())
{
queryable.OrderBy = "GETDATE()";
}
queryable.Skip(0);
queryable.Take(1);
var reval = queryable.ToList();
return(reval.First());
}
/// <summary>
/// 返回序列中的第一个元素,如果序列为NULL返回default(T)
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="queryable"></param>
/// <returns></returns>
public static T FirstOrDefault <T>(this Queryable <T> queryable)
{
if (queryable.OrderBy.IsNullOrEmpty())
{
queryable.OrderBy = "GETDATE()";
}
queryable.Skip(0);
queryable.Take(1);
var reval = queryable.ToList();
if (reval == null || reval.Count == 0)
{
return(default(T));
}
return(reval.First());
}