linq - 使用 Linq 从包含分组实体列表的 DbSet 创建自定义类的集合

Question

给定一个看起来像这样的数据集：

Iqueryable<photos> which represents the following table in a database

DataTable table = new DataTable("Trip");
table.Columns.Add("Date", typeof(string));
table.Columns.Add("Location", typeof(string));
table.Columns.Add("PhotoName", typeof(string));

table.Rows.Add("1/1/2001", "Home", "Photo1.jpg");
table.Rows.Add("1/1/2001", "Home", "Photo2.jpg");
table.Rows.Add("1/2/2001", "Work", "Photo3.jpg");
table.Rows.Add("1/2/2001", "Work", "Photo4.jpg");
table.Rows.Add("1/3/2001", "Home", "Photo5.jpg");

我想创建以下按日期和位置分组的类的集合：

 class PhotoCollection
 { 
      string date;
      string location;
      IList<string> namesOfPhotos;
 }

我开始：

 from photo in photos
 group photo by new { photo.date, photo.location };

问题：

既然项目已分组，是否可以巧妙地创建内联 PhotoCollection 的集合？

Answer 1

您可以尝试以下方法：

var result = from photo in photos
             group photo by new { date, location } into grp
             select new PhotoCollection {
                                         date = grp.Key.date,
                                         location = grp.Key.location,
                                         namesOfPhotos = grp.Select(p => p.PhotoName).ToList()
                                        }

Answer 2

尝试这个：

List<PhotoCollection> lst = 
              from t in table.AsEnumerable()
              group t by new { t.Field<string>("Location"), t.Field<string>("Date") }
              into g
              select new PhotoCollection
              {
                 date = g.Key.Date,
                 location = g.Key.Location,
                 namesOfPhotos = g.Select(c => c.Field<string>("PhotoName")).ToList()
              }

有关如何使用 linq 查询数据表的更多信息，请查看此处