获取Entity Framework中最重复的前五项记录

Question

我想从链接到Entity Framework 4.0的表中获得前五名最重复的记录。 如何在单个查询中返回五个记录的集合列表呢？

Answer 1

您只需按计数分组，按计数降序，然后使用Take（5）。 分组示例以及其他示例，可以在101 LINQ Samples中找到。

Answer 2

实际上，您应该按定义记录是否重复的字段分组。 例如，在您的情况下，该名称应类似于会员ID。 然后，您可以引入新的范围变量，该变量将保留每个组中的记录数。 使用该变量来排序结果：

var query = from s in db.Statistics
            group s by s.MemberId into g  // group by member Id
            let loginsCount = g.Count()  // get count of entries for each member
            orderby loginsCount descending // order by entries count
            select new { // create new anonymous object with all data you need
                MemberId = g.Key,
                LoginsCount = loginsCount
            };

然后先取5：

 var top5 = query.Take(5);

那将生成查询

SELECT TOP (5)                               // Take(5)
[GroupBy1].[K1] AS [MemberId],               // new { MemberId, LoginsCount }
[GroupBy1].[A1] AS [C1]
FROM ( SELECT
        [Extent1].[MemberId] AS [K1],
        COUNT(1) AS [A1]                     // let loginsCount = g.Count()
        FROM [dbo].[Statistics] AS [Extent1]
        GROUP BY [Extent1].[MemberId]        // group s by s.MemberId
)  AS [GroupBy1]
ORDER BY [GroupBy1].[A1] DESC                // orderby loginsCount descending