错误，如何实现这种功能

Question

我有一段这样的代码。

   MortgageProduct abc = ( from product in dbn.mortgageproducts
                              join scraper in dbn.mortgagescrapers
                              on product.Id equals scraper.Id
                              select cast(product, scraper)).FirstOrDefault();

并且演员功能在这里。请注意，显式转换运算符已重载 在MortgageProduct和抵押品之间

 private static MortgageProduct abc(mortgageproduct mor, mortgagescraper ms) {
            var mort = ((MortgageProduct)(mor));
                 mort.LastMonitorTime = ms.LastMonitorTime ?? DateTime.MinValue;
                 mort.NextMonitorTime = ms.NextMonitorTime ?? DateTime.MinValue;
                 return mort;
      }

但我想将强制转换函数转换为lambada表达式 我该如何实现这一功能。

  var abc =  (from product in dbn.mortgageproducts
                join scraper in dbn.mortgagescrapers
                on product.Id equals scraper.Id
                 select(() =>
                 {
                   MortgageProduct newmort = (MortgageProduct )product;
                   newmort.date = scraper.date;
                   return newmort;
                 })).FirstOrDefault();

当我尝试第二种方法时，它显示错误“连接子句中某个表达式的类型不正确。在”加入“的调用中类型推断失败”