ASP.Net【如何合并DataTable，并且去重复方法】

虽然DataTable.Merge可以很好的实现，但以下代码写出来更好理解

DataTable DataTable1 = new DataTable();
DataTable DataTable2 = new DataTable();
DataTable newDataTable = DataTable1.Clone(); 

object[] obj = new object[newDataTable.Columns.Count];
for (int i = ; i < DataTable1.Rows.Count; i++)
{
    DataTable1.Rows[i].ItemArray.CopyTo(obj,);
    newDataTable.Rows.Add(obj);
}
for (int i = ; i < DataTable2.Rows.Count; i++)
{
    DataTable2.Rows[i].ItemArray.CopyTo(obj,);
    newDataTable.Rows.Add(obj);
}
//或者
DataTable DataTable1 = new DataTable();
DataTable DataTable2 = new DataTable(); 

object[] obj = new object[DataTable1 .Columns.Count];
for (int i = ; i < DataTable2.Rows.Count; i++)
{
    DataTable2.Rows[i].ItemArray.CopyTo(obj,);
    DataTable1.Rows.Add(obj);
}

两个结构不同的DataTable合并

  /// <summary>
  /// 将两个列不同的DataTable合并成一个新的DataTable
  /// </summary>
  /// <param name="dt1">Table表1</param>
  /// <param name="dt2">Table表2</param>
  /// <param name="DTName">合并后新的表名</param>
  /// <returns></returns>

  private DataTable UniteDataTable( DataTable dt1 ,DataTable dt2 ,string DTName)
  {
   DataTable dt3 = dt1.Clone();
   for( int i =  ;i < dt2.Columns.Count ;i ++ )
   {
    dt3.Columns.Add( dt2.Columns[i].ColumnName ) ;
   }
   object[] obj = new object[dt3.Columns.Count]; 

   for (int i = ; i < dt1.Rows.Count; i++)
   {
    dt1.Rows[i].ItemArray.CopyTo(obj,);
    dt3.Rows.Add(obj);
   } 

   if( dt1.Rows.Count >= dt2.Rows.Count )
   {
    for( int i =  ;i < dt2.Rows.Count ;i++ )
    {
     for( int j =  ;j < dt2.Columns.Count ;j ++ )
     {
      dt3.Rows[i][j+dt1.Columns.Count] = dt2.Rows[i][j].ToString() ;
     }
    }
   }
   else
   {
    DataRow dr3 ;
    for( int i =  ;i < dt2.Rows.Count - dt1.Rows.Count ;i ++ )
    {
     dr3 = dt3.NewRow() ;
     dt3.Rows.Add( dr3 ) ;
    }
    for( int i =  ;i < dt2.Rows.Count ;i++ )
    {
     for( int j =  ;j < dt2.Columns.Count ;j ++ )
     {
      dt3.Rows[i][j+dt1.Columns.Count] = dt2.Rows[i][j].ToString() ;
     }
    }
   }
   dt3.TableName = DTName ;
   return dt3 ;
  } 

今天一位朋友问如何去掉DataTable里重复的记录(DataTable是别人返回过来的，不能再重新查询数据库，所以无法用sql中的select distinct xxx处理，只能在DataTable上动脑筋)

思路：将DataTable转成IEnumerable，然后就能调用Distinct方法了

System.Collections.Generic;
using System.Linq;
using System.Data;
using System; 

namespace ConsoleApplication2
{
    class Program
    {
        static void Main(string[] args)
        {
            DataTable tbl = new DataTable();
            tbl.Columns.Add("Id", typeof(System.Int32));
            tbl.Columns.Add("City", typeof(System.String));
            tbl.Columns.Add("Province", typeof(System.String)); 

            tbl.Rows.Add(, "武汉", "湖北");
            tbl.Rows.Add(, "应城", "湖北");
            tbl.Rows.Add(, "武汉", "湖北"); 

            IEnumerable <DataRow> r = tbl.AsEnumerable().Distinct(new CityComparer()); 

            //到这一步,r里就是去重复的记录了 

            foreach (var item in r)
            {
                Console.WriteLine(item["Id"] + "，" + item["City"] + "，" + item["Province"]);
            } 

            Console.ReadLine();
        } 

    } 

    class CityComparer : IEqualityComparer <DataRow>
    {
        public bool Equals(DataRow r1, DataRow r2)
        {
            return r1["City"] == r2["City"];
        } 

        public int GetHashCode(DataRow obj)
        {
            return obj.ToString().GetHashCode();
        } 

    }
}

上面的代码，将DataTable中"城市名"重复的记录去掉了,以上代码同样适用于List<T>（只要改下"比较器"即可）