Writing Database-Independent Code

[ Team LiB ] Recipe 1.11 Writing Database-Independent Code Problem You need to develop an application that can be used with different data providers, but does not lose functionality that is specific to the different providers.
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Writing Database-Independent Code[ Team LiB ]Recipe 1.11 Writing Database-Independent CodeProblemYou need to develop an application that can be used with different data providers, butdoes not lose functionality that is specific to the different providers. You want to createprovider-independent code and use it with the provider-specific code that you mightneed.SolutionThe solution shows how to use interfaces that are inherited by .NET connected classes(such as Connection and DataReader) to create provider-independent code that can beused with provider-specific code to access unique functionality.The sample code contains a method and two event handlers:GetData( ) This method is a .NET data provider-independent method that accepts .NET data provider-specific Connection and DataAdapter arguments as generic IDbConnection and IDbDataAdapter interface types. The interfaces are used to fill a DataSet from the Customers table in Northwind. The default view of the Customers DataTable is bound to the data grid on the form. Finally, the provider-specific Connection for the IDbConnection is identified and provider-specific logic executed.SQL Button.Click This event handler is provider-specific code that creates a SqlConnection and a SqlDataAdapter object and passes them as arguments into the provider- independent GetData( ) method.OLE DB Button.Click This event handler is provider-specific code that creates an OleDbConnection and an OleDbDataAdapter object and passes them as arguments into the provider- independent GetData( ) method.The C# code is shown in Example 1-9.Example 1-9. File: DatabaseIndependentCodeForm.cs// Namespaces, variables, and constantsusing System;using System.Configuration;using System.Windows.Forms;using System.Data;using System.Data.Common;using System.Data.SqlClient;using System.Data.OleDb;// . . .private void GetData(IDbConnection conn, IDbDataAdapter da){ // Create the command and assign it to the IDbDataAdapter interface. IDbCommand cmd = conn.CreateCommand( ); cmd.CommandText = SELECT * FROM Customers; da.SelectCommand = cmd; // Add a table mapping. da.TableMappings.Add(Table, Customers); dataGrid.DataSource = null; // Fill the DataSet. DataSet ds = new DataSet( ); da.Fill(ds); // Bind the default view for the Customer table to the grid. dataGrid.DataSource = ds.Tables[Customers].DefaultView; // Identify provider-specific connection type and process appropriately. if (conn is SqlConnection) { MessageBox.Show(Specific processing for SQL data provider.); } else if(conn is OleDbConnection) { MessageBox.Show(Specific processing for OLE DB data provider.); }}private void sqlButton_Click(object sender, System.EventArgs e){ // Create a SQL Connection and DataAdapter. SqlConnection conn = new SqlConnection( ConfigurationSettings.AppSettings[Sql_ConnectString]); SqlDataAdapter da = new SqlDataAdapter( ); dataGrid.CaptionText = SQL .NET Provider; // Call provider-independent function to retrieve data. GetData(conn, da);}private void oleDbButton_Click(object sender, System.EventArgs e){ // Create a OLE DB Connection and DataAdapter. OleDbConnection conn = new OleDbConnection( ConfigurationSettings.AppSettings[OleDb_ConnectString]); OleDbDataAdapter da = new OleDbDataAdapter( ); dataGrid.CaptionText = OLE DB .NET Provider; // Call provider-independent function to retrieve data. GetData(conn, da);}DiscussionThe IDbConnection, IDbCommand, IDataAdapter, and IDataReader interfaces areimplemented by Connection, Command, DataAdapter, and DataReader classes in .NETdata providers. You can pass these provider-independent base classes as interfacearguments instead of the provider-specific inherited classes. This allows applications thatsupport multiple data providers to reuse common provider-independent code.The provider-specific functionality of the classes is not available when the base interfacesare used. The is operator is used to identify the provider-specific class of the provider-independent interface. Branching logic is then used execute code specific to that class.[ Team LiB ]