我有两个表,为简化起见,如下所示:
TheFiles
FileID | UserID
23 | 342
53 | 352
TheData
UserID | DateCreated
352 | 7/22/2014
245 | 7/25/2014
589 | 7/28/2014
我想返回一个可空的int,它表示表UserID
中最新的TheData
(不在表TheFiles
中)。因此,例如,对于此示例数据,返回值将为589,因为它是TheData中的最新条目,而不在TheFiles表中。
当没有数据时,我在where
上遇到了麻烦。这就是我所拥有的:
var TheNullableInt = (from d in MyDC.TheData
where d.UserID doesn't exist in MyDC.TheFiles
orderby d.DateCreated descending
select d.UserID).FirstOrDefault();
我正在使用linq-to-SQL。我该如何处理where子句?
from d in MyDC.TheData
where !MyDC.TheFiles.Any(tf=>tf.UserID == d.UserID)
或执行join
from d in MyDC.TheData
join tf in MyDC.TheFiles on tf.UserID equals tf.UserID into j
from x in j.DefaultIfEmpty()
where x == null
select.....
var lastest = MyDC.TheData.Where(d => !MyDC.TheFiles.Any(f => f.UserID == d.UserID))
.OrderByDescending()
.FirstOrDefault();
或者,如果您really想使用LINQ
var latest = (from d in MyDC.TheData
where !MyDC.TheFiles.Any(f => f.UserID == d.UserID)
orderby d.DateCreated descending
select d
).FirstOrDefault();