选择基于null

Question

我正在构建一个动态查询并在两个实体之间进行连接：正在构建的查询和一个表。

我有：

var TheQuery = ...;

TheQuery = from x in TheQuery
           join c in MyDataContext.TheTable on
           x.ID equals c.ID
           where "there's no matching element in TheTable"
           select x

感谢您的建议。

Answer 1

要使用LINQ进行左外连接，您必须使用join .. into和DefaultIfEmpty()：

TheQuery = from x in TheQuery
           join c in MyDataContext.TheTable on x.ID equals c.ID into outer
           from o in outer.DefaultIfEmpty()
           where o == null
           select x