linq to entity 分页方法不支持LastOrDefault等操作的处理办法

最近一直使用entityframework,因为项目需要涉及到需要查询最后一条,我看着里面扩展了LastOrDefault这个方法,但是使用的时候一直报错

“LINQ to Entities 不识别方法“TravelWeb.Dao.XT_Card LastOrDefault[XT_Card](System.Linq.IQueryable`1[TravelWeb.Dao.XT_Card])”,因此该方法无法转换为存储表达式。”这样搞得我很郁闷,后来查了一下资料结果在MSDN上面查到了

支持和不支持的 LINQ 方法 (LINQ to Entities)

投影和限制方法

LINQ to Entities 查询中支持大多数 LINQ 投影和限制方法,除了那些接受位置参数的方法。 下表列出了支持的和不支持的投影和限制方法。

 

分页方法

有些 LINQ 分页方法在 LINQ to Entities 查询中不受支持。 有关更多信息,请参见 LINQ to Entities 查询中的标准查询运算符 下表列出了支持的和不支持的分页方法。

方法 支持 Visual Basic 函数签名 C# 方法签名

ElementAt

不支持

Function ElementAt(Of TSource) ( _
source As IQueryable(Of TSource), _
index As Integer _
) As TSource
TSource ElementAt<TSource>(
this IQueryable<TSource> source,
int index
)

ElementAtOrDefault

不支持

Function ElementAtOrDefault(Of TSource) ( _
source As IQueryable(Of TSource), _
index As Integer _
) As TSource
TSource ElementAtOrDefault<TSource>(
this IQueryable<TSource> source,
int index
)

First

支持

Function First(Of TSource) ( _
source As IQueryable(Of TSource) _
) As TSource
TSource First<TSource>(
this IQueryable<TSource> source
)

First

支持

Function First(Of TSource) ( _
source As IQueryable(Of TSource), _
predicate As Expression(Of Func(Of TSource, Boolean)) _
) As TSource
TSource First<TSource>(
this IQueryable<TSource> source,
Expression<Func<TSource, bool>> predicate
)

FirstOrDefault

支持

Function FirstOrDefault(Of TSource) ( _
source As IQueryable(Of TSource) _
) As TSource
TSource FirstOrDefault<TSource>(
this IQueryable<TSource> source
)

FirstOrDefault

支持

Function FirstOrDefault(Of TSource) ( _
source As IQueryable(Of TSource), _
predicate As Expression(Of Func(Of TSource, Boolean)) _
) As TSource
TSource FirstOrDefault<TSource>(
this IQueryable<TSource> source,
Expression<Func<TSource, bool>> predicate
)

Last

不支持

Function Last(Of TSource) ( _
source As IQueryable(Of TSource) _
) As TSource
TSource Last<TSource>(
this IQueryable<TSource> source
)

Last

不支持

Function Last(Of TSource) ( _
source As IQueryable(Of TSource), _
predicate As Expression(Of Func(Of TSource, Boolean)) _
) As TSource
TSource Last<TSource>(
this IQueryable<TSource> source,
Expression<Func<TSource, bool>> predicate
)

LastOrDefault

不支持

Function LastOrDefault(Of TSource) ( _
source As IQueryable(Of TSource) _
) As TSource
TSource LastOrDefault<TSource>(
this IQueryable<TSource> source
)

LastOrDefault

不支持

Function LastOrDefault(Of TSource) ( _
source As IQueryable(Of TSource), _
predicate As Expression(Of Func(Of TSource, Boolean)) _
) As TSource
TSource LastOrDefault<TSource>(
this IQueryable<TSource> source,
Expression<Func<TSource, bool>> predicate
)

Single

支持

Function Single(Of TSource) ( _
source As IQueryable(Of TSource) _
) As TSource
TSource Single<TSource>(
this IQueryable<TSource> source
)

Single

支持

Function Single(Of TSource) ( _
source As IQueryable(Of TSource), _
predicate As Expression(Of Func(Of TSource, Boolean)) _
) As TSource
TSource Single<TSource>(
this IQueryable<TSource> source,
Expression<Func<TSource, bool>> predicate
)

SingleOrDefault

支持

Function SingleOrDefault(Of TSource) ( _
source As IQueryable(Of TSource) _
) As TSource
TSource SingleOrDefault<TSource>(
this IQueryable<TSource> source
)

SingleOrDefault

支持

Function SingleOrDefault(Of TSource) ( _
source As IQueryable(Of TSource), _
predicate As Expression(Of Func(Of TSource, Boolean)) _
) As TSource
TSource SingleOrDefault<TSource>(
this IQueryable<TSource> source,
Expression<Func<TSource, bool>> predicate
)

Skip

支持

Function Skip(Of TSource) ( _
source As IQueryable(Of TSource), _
count As Integer _
) As IQueryable(Of TSource)
IQueryable<TSource> Skip<TSource>(
this IQueryable<TSource> source,
int count
)

SkipWhile

不支持

Function SkipWhile(Of TSource) ( _
source As IQueryable(Of TSource), _
predicate As Expression(Of Func(Of TSource, Boolean)) _
) As IQueryable(Of TSource)
IQueryable<TSource> SkipWhile<TSource>(
this IQueryable<TSource> source,
Expression<Func<TSource, bool>> predicate
)

SkipWhile

不支持

Function SkipWhile(Of TSource) ( _
source As IQueryable(Of TSource), _
predicate As Expression(Of Func(Of TSource, Integer, Boolean)) _
) As IQueryable(Of TSource)
IQueryable<TSource> SkipWhile<TSource>(
this IQueryable<TSource> source,
Expression<Func<TSource, int, bool>> predicate
)

Take

支持

Function Take(Of TSource) ( _
source As IQueryable(Of TSource), _
count As Integer _
) As IQueryable(Of TSource)
IQueryable<TSource> Take<TSource>(
this IQueryable<TSource> source,
int count
)

TakeWhile

不支持

Function TakeWhile(Of TSource) ( _
source As IQueryable(Of TSource), _
predicate As Expression(Of Func(Of TSource, Boolean)) _
) As IQueryable(Of TSource)
IQueryable<TSource> TakeWhile<TSource>(
this IQueryable<TSource> source,
Expression<Func<TSource, bool>> predicate
)

TakeWhile

不支持

Function TakeWhile(Of TSource) ( _
source As IQueryable(Of TSource), _
predicate As Expression(Of Func(Of TSource, Integer, Boolean)) _
) As IQueryable(Of TSource)

 



发现这么多不支持的。我现在暂时用到lastordefault  处理办法就是用orderby 一个是顺序排列一个是倒序排列,不过切记where 条件要写在前面

示例

CardStartNum =edm.XT_Card.Where(c => c.CardRuleId == s.Id).OrderBy(c => c.CardNum).FirstOrDefault(),
 CardEndNum = edm.XT_Card.Where(c => c.CardRuleId == s.Id).OrderByDescending(c => c.CardNum).FirstOrDefault()

搞定!

posted @ 2011-07-04 21:49  奇想  阅读(938)  评论(0编辑  收藏  举报