实体框架按组跳过 [英] Entity Framework skip take by group by

问题描述

我通过一个表格（表格1）对当前的分页进行分页，其中包含以下字段{Policy，Name，Amount，Date}，并且在Table1中可以有多个记录，如下所示：

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

如果我想先按策略进行分组，然后跳过并采取区分政策（基本上是为了确保一个页面包含页面中包含的策略的所有记录）？

我使用C＃，实体框架并且更喜欢$ lambda语法。

（i => i.Policy）
.Skip（endingRecord）.Take（g）页面）
.ToList（）;

生成这样的SQL（从LinqPad到Linq to SQL的示例）：

pre $ SELECT $ [t4] ，[t4]。[Date]
FROM（
SELECT ROW_NUMBER（）OVER（ORDER BY [t3]。[Policy]）AS [ROW_NUMBER]，[t3]。[test]，[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 [tl]。[Policy] = [t2]。[Policy]））
）AS [t3]
）AS [t4]
WHERE [t4]。[ROW_NUMBER] BETWEEN @ p0 + 1 AND @ p0 + @ p1
ORDER BY [t4]。[ROW_NUMBER]

I a currently "paging" through a table ("Table1") that has the following fields { Policy, Name, Amount, Date} and there can be mulitple records in "Table1" for a policy, like the following:

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

How would I do this if I wanted to first group by Policy and then skip and take on the distinct policies (basically trying to ensure that a "page" contains all the records for the policies included in the page)?

I'm using C#, entity framework and prefer the "lambda" syntax if possible.

解决方案

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

That generates SQL like this (sample from LinqPad for Linq to SQL):

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]

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