Question

 var sourceId =
            (from workstation in db.station
             join letter in db.letter on workstation.id equals letter.Site_Id
             where ThatDate < DateTime.Now.AddYears(-1)
             select workstatio).ToList();

这会生成一个列表，如果有多个列表将打印出重复，我该如何使用.distinct？

请告知，谢谢

Answer 1

 var sourceId =
            (from workstation in db.station
             join letter in db.letter on workstation.id equals letter.Site_Id
             where ThatDate < DateTime.Now.AddYears(-1)
             select workstation).Distinct().ToList();

看看这个

http://msdn.microsoft.com/en-us/library/bb338049.aspx

Answer 2

您可能需要查看DistinctBy中的MoreLinq方法。您可以将lambda表达式作为参数传递的位置。

在您的示例中，它看起来与此类似：

var sourceId =
        (from workstation in db.station
         join letter in db.letter on workstation.id equals letter.Site_Id
         where ThatDate < DateTime.Now.AddYears(-1)
         select workstatio).DistinctBy(ws => ws.Id).ToList();

您还可以将DistinctBy用于多个属性：

var sourceId =
        (from workstation in db.station
         join letter in db.letter on workstation.id equals letter.Site_Id
         where ThatDate < DateTime.Now.AddYears(-1)
         select workstatio).DistinctBy(ws => new {Id = ws.Id, OtherProperty = ws.OtherProperty}).ToList();

Btw，而不是引用比较，匿名类型实例的相等性是通过比较它们的每个属性来确定的。

我最近在这个主题上找到了一个有趣的讨论，其中Anders Hejlsberg本人建议解决这个问题。你可以阅读它here.

与LINQ截然不同

2 个答案: