LINQ To DataTable

最新推荐文章于 2019-06-26 18:09:20 发布

最新推荐文章于 2019-06-26 18:09:20 发布 · 212 阅读

本文介绍使用C#进行数据分组及按特定条件筛选记录的方法。通过创建DataTable并填充数据，利用LINQ实现按多个字段分组，并选取指定字段进行输出。此外，还展示了如何按PID字段分组，并获取每组中按CreateDate降序排列的第二条记录。

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static DataTable dtable = new DataTable(); static DataColumn dc = new DataColumn(); static DataRow Dr; static void Main() { CreateTable(); for (int i = 0; i < 3; i++) { Dr = dtable.NewRow(); Dr["MId"] = i; Dr["CId"] = i + 1; Dr["FId"] = i + 2; Dr["PId"] = i; dtable.Rows.Add(Dr); } var query = from t in dtable.AsEnumerable() group t by new { Mid = t.Field<Int32>("MId"), PId = t.Field<Int32>("PId") } into g select new { MId = g.Key.Mid, PId = g.Key.PId }; foreach (var v in query) { Console.WriteLine("{0} {1}", v.MId, v.PId); } } public static void CreateTable() { //MId CId FId PId dc = new DataColumn("MId", Type.GetType("System.Int32")); dtable.Columns.Add(dc); dc = new DataColumn("CId", Type.GetType("System.Int32")); dtable.Columns.Add(dc); dc = new DataColumn("FId", Type.GetType("System.Int32")); dtable.Columns.Add(dc); dc = new DataColumn("PId", Type.GetType("System.Int32")); dtable.Columns.Add(dc); }

2.按PID分组获取倒数第二条信息

static DataTable table = new DataTable(); static DataColumn dc = new DataColumn(); static void Main() { Createtable(); table.Rows.Add(1, 2,"2010-1-1"); table.Rows.Add(2, 3, "2010-1-1"); table.Rows.Add(3, 4, "2010-1-1"); table.Rows.Add(4, 5, "2010-1-1"); table.Rows.Add(5, 2, "2010-1-2"); table.Rows.Add(6, 3, "2010-1-2"); table.Rows.Add(7, 4, "2010-1-2"); table.Rows.Add(8, 5, "2010-1-2"); var query = from dt in table.AsEnumerable() where new int[] { 2, 3, 4 }.Contains(dt.Field<Int32>("PID")) orderby dt.Field<DateTime>("CreateDate") descending group dt by dt.Field<Int32>("PID") into g let n = (from d in g.Take(2).Skip(1) select d).FirstOrDefault() select new { ID = n.Field<Int32>("ID"), PID = g.Key, CreateDate = n.Field<DateTime>("CreateDate") }; query.ToList().ForEach(m => Console.WriteLine("{0}\t{1}\t{2}\t",m.ID,m.PID,m.CreateDate)); } public static void Createtable() { dc = new DataColumn("ID", Type.GetType("System.Int32")); table.Columns.Add(dc); dc = new DataColumn("PID", Type.GetType("System.Int32")); table.Columns.Add(dc); dc = new DataColumn("CreateDate", Type.GetType("System.DateTime")); table.Columns.Add(dc); }