Writing Database-Independent Code


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. You want to create provider-independent code and use it with the provider-specific code that you might need.


The 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 be used 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 constants
using 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( );

 // 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(
 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(
 OleDbDataAdapter da = new OleDbDataAdapter( );

 dataGrid.CaptionText = "OLE DB .NET Provider";

 // Call provider-independent function to retrieve data.
 GetData(conn, da);


The IDbConnection , IDbCommand , IDataAdapter , and IDataReader interfaces are implemented by Connection , Command , DataAdapter , and DataReader classes in .NET data providers. You can pass these provider-independent base classes as interface arguments instead of the provider-specific inherited classes. This allows applications that support multiple data providers to reuse common provider-independent code.

The provider-specific functionality of the classes is not available when the base interfaces are 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.

Connecting to Data

Retrieving and Managing Data

Searching and Analyzing Data

Adding and Modifying Data

Copying and Transferring Data

Maintaining Database Integrity

Binding Data to .NET User Interfaces

Working with XML

Optimizing .NET Data Access

Enumerating and Maintaining Database Objects

Appendix A. Converting from C# to VB Syntax

ADO. NET Cookbook
ADO.NET 3.5 Cookbook (Cookbooks (OReilly))
ISBN: 0596101406
EAN: 2147483647
Year: 2002
Pages: 222
Authors: Bill Hamilton

Flylib.com © 2008-2020.
If you may any questions please contact us: flylib@qtcs.net