实体框架中连接子句中一个表达式的类型不正确.左连接中的常量

我试图在EF查询中做一个左连接。我得到以下错误:

错误CS1941连接子句中一个表达式的类型是不正确的。调用"GroupJoin"时类型推断失败

，这里是c#代码:

var foo = from m in db.ClientMasters
                      join a in db.Orders on new { m.Id, Status = "N" } equals new { a.ClientID, a.Status } into a_join
                      from a in a_join.DefaultIfEmpty()
                      select new { m.ClientID, a.ID };

var foo = from m in db.ClientMasters
                      join a in db.Orders on new { ClientID = m.Id, Status = "N" } equals new { a.ClientID, a.Status } into a_join
                      from a in a_join.DefaultIfEmpty()
                      select new { ClientID = m.Id, OrderId = a.Id };