LINQ - 选定列

Question

我打算将以下查询转换为linQ

SELECT TOP 100 S.TxID, 
    ToEmail, 
    [Subject], 
    ProcessedDate,
    [Status] = (CASE WHEN EXISTS (SELECT TxID FROM TxBounceTracking
                            WHERE TxID = S.TxID)
                THEN 'Bounced'
                WHEN EXISTS (SELECT TxID FROM TxOpenTracking
                            WHERE TxID = S.TxID)
                THEN 'Opened'
                ELSE 'Sent' END)
FROM TxSubmissions S
WHERE S.UserID = @UserID 
AND ProcessedDate BETWEEN @StartDate AND @EndDate
ORDER BY ProcessedDate DESC

以下代码是我转换的linq。

v = (from a in dc.TxSubmissions
where a.ProcessedDate >= datefrom && a.ProcessedDate <= dateto && a.UserID == userId
let bounce = (from up in dc.TxBounceTrackings where up.TxID == a.TxID select up)
let track = (from up in dc.TxOpenTrackings where up.TxID == a.TxID select up)
select new { a.TxID, a.ToEmail, a.Subject, 
    Status = bounce.Count() > 0 ? "Bounced" : track.Count() > 0 ? "Opened" : "Sent", 
    a.ProcessedDate });

但是这个linq太慢了，因为跳转和跟踪表，我应该如何更改linq查询以选择一行只匹配上面的SQL查询＆gt;＆gt;

SELECT TxID FROM TxOpenTracking WHERE TxID = S.TxID 

在我选择的列中，因此可以更快地执行。

请注意，该记录包含一百万条记录，这就是它滞后的原因

Answer 1

由于您不会关心可读性，因为您最终会通过EF生成查询，因此您可以尝试加入这两个表。 （看起来TxID是FK或PK / FK）

有关JOIN与SUB-QUERY的更多信息，请访问：Join vs. sub-query

基本上你的SQL看起来像这样：

SELECT TOP 100 S.TxID, ToEmail, [Subject], ProcessedDate,
                [Status] = (CASE WHEN BT.TxID IS NOT NULL
                                 THEN 'Bounced'
                                 WHEN OP.TxID IS NOT NULL
                                 THEN 'Opened'
                                 ELSE 'Sent' END)
            FROM TxSubmissions S
                 LEFT JOIN TxBounceTracking BT ON S.TxID = BT.TxID
                 LEFT JOIN TxOpenTracking OP ON S.TxID = OP.TxID
                WHERE S.UserID = @UserID 
                AND ProcessedDate BETWEEN @StartDate AND @EndDate
            ORDER BY ProcessedDate DESC

然后，您可以尝试将其转换为LINQ，例如：

v = (from subs in dc.TxSubmissions.Where(sub => sub.ProcessedDate >= datefrom && sub.ProcessedDate <= dateto && sub.UserID == userId)
from bts in dc.TxBounceTrackings.Where(bt => bt.TxID == subs.TxID).DefaultIfEmpty()
from ots in dc.TxOpenTrackings.Where(ot => ot.TxID == subs.TxID).DefaultIfEmpty()
select new {   });

更多关于linq的左连接：LEFT JOIN in LINQ to entities?

此外，如果您删除默认值，如果为空，您将获得内部联接。

在这两种情况下，您还需要查看生成的SQL。