Question

我有一个where子句，用于在实体上查找子对象：

var Lookup = row.Offenses.Where(x => x.Desc == co.Desc && x.Action == co.Action && x.AppealYN == co.AppealYN && x.OffDate == co.OffDate).ToList();

有时co.OffDate可以为null，这将导致异常。现在，我能想到的唯一方法就是使用if语句：

 if (co.OffDate.HasValue)
                                {
 var Lookup = row.Offenses.Where(x => x.Desc == co.Desc && x.Action == co.Action && x.AppealYN == co.AppealYN && x.OffDate == co.OffDate).ToList();
                                }
                                else
                                {
                                     var Lookup = row.Offenses.Where(x => x.Desc == co.Desc && x.Action == co.Action && x.AppealYN == co.AppealYN).ToList();
                                }

无论如何我可以重写linq查询来完成if语句的作用吗？即使co.OffDate为空，我仍然想要进行查找。

Answer 1

您可以在Where过滤器中插入三元组：

var Lookup = row.Offenses
  .Where(x => 
    x.Desc == co.Desc 
    && x.Action == co.Action 
    && x.AppealYN == co.AppealYN 
    && (co.OffDate.HasValue ? x.OffDate == co.OffDate : true)
  ).ToList();

Answer 2

我会把它重写为更具可读性（在我看来）：

var query = row.Offenses.Where(x => x.Desc == co.Desc 
                                    && x.Action == co.Action 
                                    && x.AppealYN == co.AppealYN)
if (co.OffenseDate.HasValue)
{
  query = query.Where(x.OffDate == co.OffenseDate);
}

var Lookup = query.ToList();

LINQ to Entities：where子句中的nullable datetime

2 个答案: