使用Linq执行多个左连接

Question

我有四张桌子。我想在表上执行多个左连接，如下所示。

from t1 in table1
join t2 in table2 on <condition1>
into join1
from subJoin1 in join1.DefaultIfEmpty()
join t3 in table3 on <condition2>
into join2
from subjoin2 in join2.DefaultIfEmpty()
join t4 in table4 on <condition3>
into join3
from subjoin3 in join3.DefaultIfEmpty()
select new

{
Field1 = t1.some_field,
Field2 =  t2.some_field,
Field3 =  t3.some_field,
Field4 =  t4.some_field,
}

我的问题是第一个左连接单独工作正常，但是当左连接连续完成时，如果在t3，t4等中找不到映射，则t1数据行会丢失。

请帮忙。

Answer 1

您不需要into（至少马上就开始）！

像

这样的东西

from t1 in table1
join t2 in table2 on <inner_join_condition>
from t3 in table3.Where(<left_outer_join_condition>).DefaultIfEmpty()
...
select new
{
Field1 = t1.some_field,
Field2 = t3.some_field,
...
}

通常效果很好！