C# dataset存放多张表的实例

cmd.CommandText = "select * from table1;";
NpgsqlDataAdapter da = new NpgsqlDataAdapter(cmd); //实例化一个类，它用于连接C#与数据库，并执行cmd语句且将结果缓存到适配器中
DataSet thedataset = new DataSet(); //实例化一个dataset，实例名为thedataset（通常被定义为ds）
da.Fill(thedataset, "thetable1"); //将适配器中的内容填充到dataset的thetable1表中， thetable1同时被建立
cmd.Parameters.Clear(); //清空cmd内容，如果不清空下次使用时会抛出异常
cmd.CommandText = "select * from table2;";
da = new NpgsqlDataAdapter(cmd);
da.Fill(thedataset, "thetable2"); //将适配器中的内容填充到dataset的thetable2表中， thetable2同时被建立
cmd.Parameters.Clear(); //清空cmd内容
...
int count = thedataset.Tables["thetable1"].Rows.Count; //获取表thetable1的行数
string a = thedataset.Tables["thetable2"].Rows[1][0].ToString().; //获取表thetable2第2行第1列的值

DataRelation custOrderRel = ds.Relations.Add("CustOrders", ds.Tables["Customers"].Columns["CustomerID"], ds.Tables["Orders"].Columns["CustomerID"]);

static void Main(string[] args)
    {
      string connStr = @"Data Source=.\SQLEXPRESS; AttachDbFilename='C:\SQL Sever 2000 Sample Databases\NORTHWND.MDF';Integrated Security=True;User Instance=true";
      SqlConnection conn = new SqlConnection(connStr);
      conn.Open();
      //创建用于保存修改的数据的适配器
      SqlDataAdapter adapter = new SqlDataAdapter("select CustomerID,CompanyName from Customers", conn);
      SqlCommandBuilder builder = new SqlCommandBuilder(adapter);
      //创建数据集
      DataSet ds = new DataSet();
      //创建读取Customers表的适配器
      SqlDataAdapter custAdapter = new SqlDataAdapter("select * from Customers", conn);
      //创建读取Orders表的适配器
      SqlDataAdapter orderAdapter = new SqlDataAdapter("select * from Orders", conn);
      //填充两个表的数据并放到DataSet中
      custAdapter.Fill(ds, "Customers");
      orderAdapter.Fill(ds, "Orders");
      //创建两个表之间的关系
      DataRelation custOrderRel = ds.Relations.Add("CustOrders", ds.Tables["Customers"].Columns["CustomerID"], ds.Tables["Orders"].Columns["CustomerID"]);
      foreach (DataRow custRow in ds.Tables["Customers"].Rows)
      {
        Console.WriteLine("Customer ID: " + custRow["CustomerID"] + "\tName: " + custRow["CompanyName"]);
        foreach (DataRow orderRow in custRow.GetChildRows(custOrderRel))
        {
          Console.WriteLine(" Order ID: "+orderRow["OrderID"]);
        }
      }
      conn.Close();
 
      Console.ReadKey();
 
    }

      var preferredCustomers = from c in Customers
                   where c.GetChildRows("CustOrders").Length > 10
                   orderby c.GetChildRows("CustOrders").Length
                   select c;
      Console.WriteLine("Customers with > 10 orders:");
      foreach (var customer in preferredCustomers)
      {
        Console.WriteLine("{0} orders: {1} {2}, {3} {4}",customer.GetChildRows("CustOrders").Length,
          customer["CustomerID"],customer["CompanyName"],customer["City"],customer["Region"]);
      }