Tài liệu Creating Child DataView Objects doc

Creating Child DataView Objects You can create a child DataView from a parent DataRowView using the CreateChildView() method. You can then view the DataRowView objects from the child DataView. To call the CreateChildView() method, you must first add a DataRelation to the DataSet that defines a relationship between the two underlying DataTable objects. (See Chapter 12 , "Navigating and Modifying Related Data," for information about DataRelation objects.) Let's take a look at an example. Assume you have two DataTable objects named customersDT and ordersDT. Also assume you've added the following DataRelation to the DataSet that defines a relationship between customersDT and ordersDT: DataRelation customersOrdersDataRel = new DataRelation( "CustomersOrders", customersDT.Columns["CustomerID"], ordersDT.Columns["CustomerID"] ); myDataSet.Relations.Add( customersOrdersDataRel ); Finally, assume you have a DataView named customersDV that views the customers that have a Country column of UK. You can then call the CreateChildView() method from a DataRowView in customersDV to create a child DataView; notice that the name of the DataRelation (CustomersOrders) is passed to the CreateChildView() method: DataView ordersDV = customersDV[0].CreateChildView("CustomersOrders"); The ordersDV DataView allows you to access the child rows from the ordersDT DataTable. The parent in this example is the first DataRowView from customersDV with a CustomerID of AROUT. The child ordersDV DataView contains DataRowView objects with the details of the orders for the AROUT customer. N ote The CreateChildView() method is overloaded. The other version of this method accepts a DataRelation object as the parameter. Listing 13.4 shows a complete example program. Listing 13.4: CREATECHILDDATAVIEW.CS /* CreateChildDataView.cs illustrates how to create a child DataView */ using System; using System.Data; using System.Data.SqlClient; class CreateChildDataView { public static void Main() { SqlConnection mySqlConnection = new SqlConnection( "server=localhost;database=Northwind;uid=sa;pwd=sa" ); SqlCommand mySqlCommand = mySqlConnection.CreateCommand(); mySqlCommand.CommandText = "SELECT CustomerID, CompanyName, Country " + "FROM Customers;" + "SELECT OrderID, CustomerID " + "FROM Orders;"; SqlDataAdapter mySqlDataAdapter = new SqlDataAdapter(); mySqlDataAdapter.SelectCommand = mySqlCommand; DataSet myDataSet = new DataSet(); mySqlConnection.Open(); mySqlDataAdapter.Fill(myDataSet); mySqlConnection.Close(); myDataSet.Tables["Table"].TableName = "Customers"; myDataSet.Tables["Table1"].TableName = "Orders"; DataTable customersDT = myDataSet.Tables["Customers"]; DataTable ordersDT = myDataSet.Tables["Orders"]; // add a DataRelation object to myDataSet DataRelation customersOrdersDataRel = new DataRelation( "CustomersOrders", customersDT.Columns["CustomerID"], ordersDT.Columns["CustomerID"] ); myDataSet.Relations.Add( customersOrdersDataRel ); // create a DataView object named customersDV DataView customersDV = new DataView(); customersDV.Table = customersDT; customersDV.RowFilter = "Country = 'UK'"; customersDV.Sort = "CustomerID"; // display the first row in the customersDV DataView object Console.WriteLine("Customer:"); for (int count = 0; count < customersDV.Table.Columns.Count; count++) { Console.WriteLine(customersDV[0][count]); } // create a child DataView named ordersDV that views // the child rows for the first customer in customersDV DataView ordersDV = customersDV[0].CreateChildView("CustomersOrders"); // display the child rows in the customersDV DataView object Console.WriteLine("\nOrderID's of the orders placed by this customer:"); foreach (DataRowView ordersDRV in ordersDV) { Console.WriteLine(ordersDRV["OrderID"]); } } } The output from this program is as follows: Customer: AROUT Around the Horn UK OrderID's of the orders placed by this customer: 10355 10383 10453 10558 10707 10741 10743 10768 10793 10864 10920 10953 11016 . Creating Child DataView Objects You can create a child DataView from a parent DataRowView using the CreateChildView() method. You. example program. Listing 13.4: CREATECHILDDATAVIEW.CS /* CreateChildDataView.cs illustrates how to create a child DataView */ using System; using