entity framework跳过按组分组

我目前通过一个表（“Table1”）“分页”，其中包含以下字段{Policy，Name，Amount，Date}，并且“Table1”中可以有多个记录，如下所示：

return context.Table1s.Orderby(i => i.Policy) .Skip(endingRecord).Take(page) .ToList(); 

如果我想首先按策略分组然后跳过并采用不同的策略（基本上试图确保“页面”包含页面中包含的策略的所有记录），我将如何执行此操作？

我正在使用C＃，entity framework，如果可能的话，更喜欢“lambda”语法。

Answer 1

 return context.Table1s.GroupBy(i => i.Policy) .Select(g => g.First()) .Orderby(i => i.Policy) .Skip(endingRecord).Take(page) .ToList(); 

这会生成这样的SQL（从LinqPad到Linq到SQL的示例）：

 SELECT [t4].[test], [t4].[Name], [t4].[Policy], [t4].[Amount], [t4].[Date] FROM ( SELECT ROW_NUMBER() OVER (ORDER BY [t3].[Policy]) AS [ROW_NUMBER], [t3].[test], [t3].[Name], [t3].[Policy], [t3].[Amount], [t3].[Date] FROM ( SELECT [t0].[Policy] FROM Table1s AS [t0] GROUP BY [t0].[Policy] ) AS [t1] OUTER APPLY ( SELECT TOP (1) 1 AS [test], [t2].[Name], [t2].[Policy], [t2].[Amount], [t2].[Date] FROM Table1s AS [t2] WHERE (([t1].[Policy] IS NULL) AND ([t2].[Policy] IS NULL)) OR (([t1].[Policy] IS NOT NULL) AND ([t2].[Policy] IS NOT NULL) AND ([t1].[Policy] = [t2].[Policy])) ) AS [t3] ) AS [t4] WHERE [t4].[ROW_NUMBER] BETWEEN @p0 + 1 AND @p0 + @p1 ORDER BY [t4].[ROW_NUMBER] 

Answer 2

以下给了我想要的结果

  return context.Tables1 .Where(i => context.Tables1 .GroupBy(t => t.Policy) .OrderBy(t => t.Key) .Skip(previousRecordCount).Take(page) .Select(t => t.Key) .Contains(i.Policy)) .ToList(); 

Answer 3

您可以使用SkipWhile和TakeWhile方法，但您需要按如下方式将其分开：

 var policyStart = context.Table1s.Orderby(i => i.Policy).ToList().SkipWhile(i => i.Policy == endingRecord.Policy); var firstPolicy = policyStart.FirstOrDefault().Policy; return policyStart.TakeWhile(i => i.Policy == firstPolicy).ToList();