Question

我正在使用Linq To SQL从数据表中获取数据。我想在where子句中使用let语句的结果。

例如： -

from t1 in table1
      join t2 in table2
      on t1.field1 equals t2.field2
      let calculatedValue = t2.val1 + t2.val2
      join t3 in table3
      on t2.somefield equals t3.somefield
      into t3Grp
      from subt3 in t3Grp.DefaultIfEmpty()
      [select the row in table3 with where table3.someValue < calculatedValue]

我在computeValue中遇到的问题无法在table3的.Where()子句中访问。我想完全左连接输出（即;即使table3中没有行someValue < calculatedValue我想要输出中的那行。请帮忙。

Answer 1

试试这个：

from t1 in table1
  join t2 in table2
  on t1.field1 equals t2.field2
  let calculatedValue = t2.val1 + t2.val2
  join t3 in table3.where(item => item.someValue < calculatedValue)
  on t2.somefield equals t3.somefield
  into t3Grp
  from subt3 in t3Grp.DefaultIfEmpty()
  select new
  {
    val1= table3.val1,
    val2 = table3.val2,
    .
    .
    .
  }

Answer 2

您是否可以通过在最终t3Grp中限制select来执行此操作，例如

from t1 in table1
join t2 in table2
on t1.field1 equals t2.field2
let calculatedValue = t2.val1 + t2.val2
join t3 in table3
on t2.somefield equals t3.somefield
into t3Grp
from subt3 in t3Grp.DefaultIfEmpty()
select new { t1, t2, t3Grp = t3Grp.Where(t3 => t3.someValue < calculatedValue) }

值的范围，我只是不确定你想要的确切投影。

在where子句LinQ中使用let的结果

2 个答案: