LINQ选择表达式IEnumerable

Question

我正试图用一个Expression内部LINQ Select.这是我的代码示例

Expression<Func<user, string>> expr = d => d.user.username;
Message.Select(b => new { name = b.user.Select(expr) });

消息属于类型IEnumerable,在运行时我收到以下错误: The exception message is ''System.Collections.Generic.List<W.Models.user>' does not contain a definition for 'Select'

我该如何解决？

Answer 1

听起来你错过了using System.Linq;代码文件的顶部.但请注意,这List<T>是LINQ-to-Objects; 失去了Expression:

Func<user, string> expr = d => d.user.username;
Message.Select(b => new { name = b.user.Select(expr) });

最后的想法; 当有关System.Collections.Generic.List<W.Models.user>建议列表的消息时,您的代码(b.User.Select/ Message.Select)会建议单个对象.这......令人困惑.