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10.3 Reading points

  1. Change the code inside the if (connection != null) block as follows: 

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    if (connection != null)
{
    Console.WriteLine("Connection established!");
    string sql = "SELECT * FROM Point;";
    try
    {
        MySqlCommand command = new MySqlCommand(sql, connection);
        using MySqlDataReader reader = command.ExecuteReader();
        while (reader.Read())
        {
            double x = reader.GetDouble("xcoordinate");
            double y = reader.GetDouble("ycoordinate");
            Console.WriteLine($"({x:F2}, {y:F2})");
        }
        connection.Close();
    }
    catch (MySqlException ex)
    {
        Console.WriteLine(ex);
    }
}

    This is the standard way to read data from a database.

    • The query is in the string sql. In this case, all rows from the Point table are retrieved.
    • The results are returned in a MySqlDataReader.
    • The while-loop iterates through the rows. Columns are accessed by column name (as defined in Workbench).
    • After execution, the connection can be closed.

  2. Try some other queries, such as "SELECT * FROM Circle WHERE radius > 5" and display the radius of the returned circles. Adjust the code in the while-loop accordingly.