如何在Linq to SQL中使用distinct with group

Question

我正在尝试将以下sql转换为Linq 2 SQL:

select groupId, count(distinct(userId)) from processroundissueinstance 
group by groupId

这是我的代码:

var q = from i in ProcessRoundIssueInstance
    group i by i.GroupID into g
    select new
    {
        Key = g.Key,
        Count = g.Select(x => x.UserID).Distinct().Count()
    };

当我运行代码时,我不断获得无效的GroupID.有任何想法吗？看起来不同的是搞砸了......

这是生成的sql:

SELECT [t1].[GroupID] AS [Key], (
SELECT COUNT(*)
FROM (
    SELECT DISTINCT [t2].[UserID]
    FROM [ProcessRoundIssueInstance] AS [t2]
    WHERE (([t1].[GroupID] IS NULL) AND ([t2].[GroupID] IS NULL)) 
       OR (([t1].[GroupID] IS NOT NULL) 
            AND ([t2].[GroupID] IS NOT NULL) 
            AND ([t1].[GroupID] = [t2].[GroupID]))
    ) AS [t3]
) AS [Count]
FROM (
    SELECT [t0].[GroupID]
    FROM [ProcessRoundIssueInstance] AS [t0]
    GROUP BY [t0].[GroupID]
    ) AS [t1]

Answer 1

我认为Basiclife很接近,但是检查id是否为空可能不是问题或者足够,你应该检查以确保它在执行组之前不是null,因为你说它是一个可以为空的字段.否则它看起来是正确的,如果你遇到问题,你可能有错误的数据,或者它是一个错误或没有完全实现的Linq to SQL功能,你可能想尝试Linq to Entity.

var q = from i in ProcessRoundIssueInstance
        where i.GroupID != null
        && i.GroupID != string.Empty
        group i by i.GroupID into g        
        select new
        {
            Key = g.Key,
            Count = g.Select(x => x.UserID).Distinct().Count()
        };

Answer 2

根据这篇文章，您的代码看起来是正确的：

使用 GROUP BY 和 COUNT(DISTINCT) 的 LINQ to SQL

您是否尝试过检查生成的 SQL？