LINQ To DataTable

最新推荐文章于 2019-06-26 18:09:20 发布

原创最新推荐文章于 2019-06-26 18:09:20 发布 · 1.3w 阅读

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#linq #2010 #query #table

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本文介绍了使用DataTable和 LINQ 对数据进行操作和分组查询的方法，包括创建表、添加数据、分组并获取特定信息。

		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);
		}