/// <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">表实体类型</typeparam>
/// <param name="queryable">查询对象</param>
/// <returns>T</returns>
public static T Single <T>(this Queryable <T> queryable)
{
if (queryable.OrderByValue.IsNullOrEmpty())
{
queryable.OrderByValue = "now()";
}
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">表实体类型</typeparam>
/// <param name="queryable">查询对象</param>
/// <returns>T</returns>
public static T First <T>(this Queryable <T> queryable)
{
if (queryable.OrderByValue.IsNullOrEmpty())
{
queryable.OrderByValue = "now()";
}
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">表实体类型</typeparam>
/// <param name="queryable">查询对象</param>
/// <returns>T</returns>
public static T FirstOrDefault <T>(this Queryable <T> queryable)
{
if (queryable.OrderByValue.IsNullOrEmpty())
{
queryable.OrderByValue = "now()";
}
queryable.Skip(0);
queryable.Take(1);
var reval = queryable.ToList();
if (reval == null || reval.Count == 0)
{
return(default(T));
}
return(reval.First());
}
/// <summary>
/// 专门用于分页控件
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="allItems"></param>
/// <param name="pageIndex"></param>
/// <param name="pageSize"></param>
/// <returns></returns>
public static PagedList <T> ToPagedList <T>(this Queryable <T> allItems, int pageIndex, int pageSize)
{
if (pageIndex < 1)
{
pageIndex = 1;
}
var itemIndex = (pageIndex - 1) * pageSize;
var totalItemCount = allItems.Count();
while (totalItemCount <= itemIndex && pageIndex > 1)
{
itemIndex = (--pageIndex - 1) * pageSize;
}
var pageOfItems = allItems.Skip(itemIndex).Take(pageSize).ToList();
return(new PagedList <T>(pageOfItems, pageIndex, pageSize, totalItemCount));
}
