EF Core - 从特定列计数

Question

我几乎让我的 EF Core 查询正常工作...这是生成的 SQL（注意 Count(*)：

SELECT [u].[Key], [u].[Url], [u].[CreatedBy], [u].[CreatedOn], COUNT(*) AS [Clicks]
FROM [URLs] AS [u]
LEFT JOIN [OwnerUrls] AS [o] ON [u].[Key] = [o].[ShortUrlKey]
LEFT JOIN [Clicks] AS [c] ON [u].[Key] = [c].[ShortUrlKey]
GROUP BY [u].[Key], [u].[Url], [u].[CreatedBy], [u].[CreatedOn]

我需要的是（让 Count 查看特定的列/表）

SELECT [u].[Key], [u].[Url], [u].[CreatedBy], [u].[CreatedOn], COUNT(c.ID) AS [Clicks]
FROM [URLs] AS [u]
LEFT JOIN [OwnerUrls] AS [o] ON [u].[Key] = [o].[ShortUrlKey]
LEFT JOIN [Clicks] AS [c] ON [u].[Key] = [c].[ShortUrlKey]
GROUP BY [u].[Key], [u].[Url], [u].[CreatedBy], [u].[CreatedOn]

这是我正在使用的 EF 查询...

            query = (from u in db.URLs
                         join ou in db.OwnerUrls on u.Key equals ou.ShortUrlKey into urlOwners
                         from subSet in urlOwners.DefaultIfEmpty()
                         join c in db.Clicks on u.Key equals c.ShortUrlKey into urlClicks
                         from subClicks in urlClicks.DefaultIfEmpty()

                         group subClicks by new { u.Key, u.Url, u.CreatedBy, u.CreatedOn } into g
                         select new ShortURL()
                         {
                             Key = g.Key.Key,
                             Url = g.Key.Url,
                             CreatedBy = g.Key.CreatedBy,
                             CreatedOn = g.Key.CreatedOn,
                             Clicks = g.Count()
                         });

我尝试将 g.Count() 更改为 g.Select(x=>x.Id).Count() ，这只会导致 EF Core 抱怨并抱怨客户端评估与服务器端评估等。 .

我应该提到，我加入第一个模型 (OwnerUrls) 的原因是为了支持我没有在此处包含的 where 子句...

谢谢！

Answer 1

我不是 EF 开发人员，但使用 SQL Server 已经有一段时间了。在 SQL Server 中，我将使用 COUNT(DISTINCT c.ID) 来消除您可能从 JOINS 获得的任何重复项。

如果由于模型而无法重复，则 COUNT(*) 应该足够了。

也许这可能会有所帮助： https://entityframeworkcore.com/knowledge-base/51892585/linq-select-distinct-count-performed-in-memory