The ADO.NET OleDbDataReader class

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Introduction

ADO.NET is the .NET enhanced version of ADO that we all know and love. ADO.NET aims to address some of the deficiencies of traditional ADO and present a model that provides type safety, OOP, and efficiency.

This article will demonstrate the most common task when accessing a database: querying for data and traversing that data from start to finish in order to display the contents (or subset thereof) of a table.

The DataReader class

ADO.NET replaces the concept of data rows with the DataSet object. This essentially provides us with full access to a given database, including all rows, tables and relationships in an object oriented and type-safe manner. It is, however, total overkill for the simple query and traversals that are most often performed on databases.

For this simple case .NET provides us with the DataReader class (OleDbDataReader, OdbcDataReader and SqlDataReader) that is essentially a type safe read only, forward only rowset. The differences between the various flavours of DataReaders is in which data access library they use. SqlDataReader works best with SQL Server, while the others work best with ODBC and OleDB data srouces.

All we need to do is open a connection to a database, send an SQL command, then traverse through the resultant DataReader using the Read command and process the results.

The easiest way to illustrate this is to show you some code. This snippet opens an Access database, reads all the information from a table, then populates a List View control with the data inside.

A few notes on the code:

• StatusText and fileName are RichTextBox controls declared as

  private System.Windows.Forms.RichTextBox fileName;
  private System.Windows.Forms.RichTextBox StatusText;

• listView is a list view control declared as

  System.WinForms.ListView listView;
  listView = new System.Windows.Forms.ListView ();

  The list view has been placed in details mode using

  listView.View = System.Windows.Forms.View.Details;

The Code

OleDbConnection Connection = new OleDbConnection ();

try
{
    // Open a connection to the database
    Connection.ConnectionString = "Provider=Microsoft.Jet.OLEDB.4.0;" +
                                  "Data Source=" + fileName.Text + ";" +
                                  "Persist Security Info=False;";
    Connection.Open();

    // Create an OleDb command, 
    OleDbCommand command = new OleDbCommand();
    command.Connection = Connection;
    command.CommandText = "SELECT * FROM Authors";

    // Execute and return the rows in the data reader object
    OleDbDataReader dataReader;
    dataReader = command.ExecuteReader(CommandBehavior.CloseConnection);

    int nFields = dataReader.FieldCount;

    // Setup the columns in the listview using the fields in the table
    listView.Clear();
    for (int i = 0; i < nFields; i++)
    {
        listView.Columns.Add(dataReader.GetName(i), 100, 
                             HorizontalAlignment.Left);
    }

    // Fill the rows in the listview using the data in the rows
    int nRow = 0;
    while (dataReader.Read())
    {
        // Create an array of subitems for quick insertion
        // The subitems will be all fields in the row except for 
        // the first field
        String [] subitems = new String[nFields];
        for (int i = 0; i < nFields; i++)
        {
            subitems[i] = dataReader[i].ToString();
        }

        // Insert a new item into the listview, and add the subitems at 
        // the same time. The item will be the first field in the row
        ListViewItem item = new ListViewItem(subitems, -1);
        listView.Items.Add(item);

        ++nRow;
    }    
    dataReader.Close();

    // Set the status text
    StatusText.Text = nFields.ToString() + " columns, " + 
          nRow.ToString() + " rows read";
}
catch (Exception ex)
{
    // If an error occured alert the user
    StatusText.Text = "Error: " + ex.Message;
}
finally
{
    // Close the connection if necessary
    if (Connection.State == System.Data.ConnectionState.Open)
        Connection.Close();
}

That's all there is to it. We have closed the database connection but since we are using managed code there is no need (or way) to delete the objects and memory we allocated.

History

23 Aug 2003 - Updated to .NET 1.0/1.1. Previous version was for .NET beta 1.