Question

我有以下查询：

var content = (from ca in db.ContentAccesses 
               where !candidateList.Contains(ca.Content) &&
                     ca.DateAccessed >= DateTime.Now.AddDays(-90)
               group ca by ca.ContentId)
               .OrderByDescending(c => c.Count()).Take(5);

哪个解析为以下T-SQL

SELECT TOP (5) [t1].[ContentId] AS [Key]
FROM (
    SELECT COUNT(*) AS [value], [t0].[ContentId]
    FROM [dbo].[ContentAccesses] AS [t0]
    WHERE (NOT ([t0].[ContentId] = @p0)) AND ([t0].[DateAccessed] >= @p1)
    GROUP BY [t0].[ContentId]
    ) AS [t1]
ORDER BY [t1].[value] DESC

但我需要实际的“内容”对象，而不仅仅是ContentId ...所以我尝试在select ca.Content之后添加group by，但编译器会抱怨。

ContentAcceses有一个FK（ContentId）到内容表。

我还不太了解LINQ。

Answer 1

您需要向下展平分组以从组中获取单个对象。但是，由于您希望对每个ContentAccess的{{1}}进行分组，因此您也应将其分组。

Content

为了获得更简单的等效TSQL查询，您可能希望使用LINQ to Objects进行展平并获得前5个。

var content = (from ca in db.ContentAccesses 
               where !candidateList.Contains(ca.Content)
                  && ca.DateAccessed >= DateTime.Now.AddDays(-90)
               group ca by ca.ContentId into g
               orderby g.Count() descending
               from ca in g        // flatten the group
               select ca)
              .Take(5);

Answer 2

var content =  (from ca in db.ContentAccesses 
               where !candidateList.Contains(ca.Content) &&
                     ca.DateAccessed >= DateTime.Now.AddDays(-90)
               group ca by ca.ContentId into cag
               select new
               {
                 ContentId = cag.Key,
                 Contents = cag
               }).OrderByDescending(c => c.Contents.Count()).Take(5);

帮助这个LINQ to SQL查询

2 个答案: