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我试图在3个表之间执行左外部联接。但是,在创建输出时,会发生NullReferenceException。可空的DateTime在左外部联接
我已经尝试了几个选项,检查日期是否为空,并将日期时间转换为可为空的值。
如何在DateTime列上执行左外连接?
var query = from t1 in A
join t2 in B
on t1.newAsset equals t2.newAsset into grp1
join t3 in C
on t1.newAsset equals t3.newAsset into grp2
from t2 in grp1.DefaultIfEmpty()
from t3 in grp2.DefaultIfEmpty()
select new
{
asset = t1.newAsset,
standbyIssuedBeforeTarget = t1.issueDate
standbyReturnedBeforeTarget = (DateTime?)t2.issueDate // Tried casting to a nullable date
//standbyReturnedDuringTarget = (t3.issueDate == null ? SqlDateTime.Null : t3.issueDate) // Tried comparing issueDate to null
};