c# – ADO .NET中的可组合查询每次迭代都会返回更多实体

堆栈溢出！

我有一个MS sql数据库.该数据库的一部分将在下一张图片中显示

我正在尝试进行可压缩的查询,我正在尝试查找具有特定evEventKindID事件的患者.例如,我想找到具有(evEventKindtID == 1)事件和具有(evEventKindID == 1)事件的患者.

var query = from pt in db.tblPatient
            select pt;
var list = query.ToList();// {1}

foreach (var limit in group.limits.Values)
{
      if (limit.eventKind.Type == TypeOfEventKind.ekEvent)
      {
           query = from pt in query
           where (pt.tblEvent.Count(j => j.evEventKindID == limit.eventKind.ID) > 0)
                                select pt;// {2}

           list = query.ToList();
           MessageBox.Show(query.Count().ToString());
      }
 }

问题是每次下一次迭代都可以返回比前一次更多的元素.它为我辩护.如何从查询中查询返回比第一个查询更多的实体？

在sql Server Profiler中,我发现了由ADO .NET EF生成的SQL查询.在{1}的地方：

SELECT 
[Extent1].[ptID] AS [ptID],[Extent1].[ptFullName] AS [ptFullName],[Extent1].[ptHomeAddress] AS [ptHomeAddress],[Extent1].[ptPhone] AS [ptPhone],[Extent1].[ptBirthDate] AS [ptBirthDate],[Extent1].[ptIsMale] AS [ptIsMale],[Extent1].[ptUserID] AS [ptUserID],[Extent1].[ptINN] AS [ptINN],[Extent1].[ptSNILS] AS [ptSNILS]
FROM [dbo].[tblPatient] AS [Extent1]

在第一次迭代的位置{2}：

exec sp_executesql N'SELECT 
[Project1].[ptID] AS [ptID],[Project1].[ptFullName] AS [ptFullName],[Project1].[ptHomeAddress] AS [ptHomeAddress],[Project1].[ptPhone] AS [ptPhone],[Project1].[ptBirthDate] AS [ptBirthDate],[Project1].[ptIsMale] AS [ptIsMale],[Project1].[ptUserID] AS [ptUserID],[Project1].[ptINN] AS [ptINN],[Project1].[ptSNILS] AS [ptSNILS]
FROM ( SELECT 
    [Extent1].[ptID] AS [ptID],[Extent1].[ptSNILS] AS [ptSNILS],(SELECT 
        COUNT(1) AS [A1]
        FROM [dbo].[tblEvent] AS [Extent2]
        WHERE ([Extent1].[ptID] = [Extent2].[evPatientID]) AND ([Extent2].[evEventKindID] = @p__linq__0)) AS [C1]
    FROM [dbo].[tblPatient] AS [Extent1]
)  AS [Project1]
WHERE [Project1].[C1] > 0',N'@p__linq__0 int',@p__linq__0=29

在第二次迭代的地方{2}：

exec sp_executesql N'SELECT 
[Project2].[ptID] AS [ptID],[Project2].[ptFullName] AS [ptFullName],[Project2].[ptHomeAddress] AS [ptHomeAddress],[Project2].[ptPhone] AS [ptPhone],[Project2].[ptBirthDate] AS [ptBirthDate],[Project2].[ptIsMale] AS [ptIsMale],[Project2].[ptUserID] AS [ptUserID],[Project2].[ptINN] AS [ptINN],[Project2].[ptSNILS] AS [ptSNILS]
FROM ( SELECT 
    [Project1].[ptID] AS [ptID],[Project1].[ptSNILS] AS [ptSNILS],(SELECT 
        COUNT(1) AS [A1]
        FROM [dbo].[tblEvent] AS [Extent3]
        WHERE ([Project1].[ptID] = [Extent3].[evPatientID]) AND ([Extent3].[evEventKindID] = @p__linq__1)) AS [C1]
    FROM ( SELECT 
        [Extent1].[ptID] AS [ptID],(SELECT 
            COUNT(1) AS [A1]
            FROM [dbo].[tblEvent] AS [Extent2]
            WHERE ([Extent1].[ptID] = [Extent2].[evPatientID]) AND ([Extent2].[evEventKindID] = @p__linq__0)) AS [C1]
        FROM [dbo].[tblPatient] AS [Extent1]
    )  AS [Project1]
    WHERE [Project1].[C1] > 0
)  AS [Project2]
WHERE [Project2].[C1] > 0',N'@p__linq__0 int,@p__linq__1 int',@p__linq__0=31,@p__linq__1=31

你怎么看待这个问题？

解决方法

这是与foreach的常见混淆.引用变量的查询在执行查询时获取其参数值,而不是在绑定参数时获取.所以你可以拥有

int orderId = 1;
var query = from o in context.Orders where o.Id == orderId;
orderId = 2;
MessageBox.Show(query.Single().Id.ToString()); // shows that order 2 was retrieved

在您的情况下,您的foreach循环有一个变量限制.你多次引用它,但那些多个引用都看到相同的值.这就是你看到的原因

N'@p__linq__0 int,@p__linq__1=31

两个参数都具有值31,第一次迭代中的29都消失了.

最简单的方法是每次创建一个新变量：

foreach (var limit in group.limits.Values)
{
    var locallimit = limit;
    // refer to locallimit in your query,not to limit
}