Creating Child DataView Objects

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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.

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Nội dung Text: Creating Child DataView Objects

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. Note 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