problem with methods and classes

[nephish]

Hey there,
i am having a problem understanding how to get a method to update a class variable.

here is the class

class Field
{
    var $customer, $name, $sensor;

function Field($customer, $name)
{
    $this->customer = $customer;
    $this->name = $name;        
    $query = mysql_query("SELECT  `control_option`
                        FROM `Fields`
                        WHERE `Customer_ID` = '{$this->customer}'
                        AND `name` = '{$this->name}' ");
    $row = mysql_fetch_row($query);        
    $this->control_option = $row[0]; 
}
function set_control_option($option)
{
    $sensor = $this->sensor;
    mysql_query("UPDATE `Fields` SET `control_option` = '{$option}'
                WHERE `Sensor_ID` = '{$sensor}' ");
    $this->control_option = $option;

}

}

then the class is called from another script

$field = new Field;
$control_option = '4'
print 'old control_option = '.$field->control_option.'<br>';
$field->set_control_option($control_option);
print 'new control_option = '.$field->control_option;

but, i am not getting anything out of it.
the database entry is empty, which happens if i send it an empty value in a query.
So the function is doing something. But i can't seem to get where i am going wrong here. The print statement

print 'new control_option = '.$field->control_option;

isn't giving me anything.

if you have read this far, thanks for your time, any idea what i am doing wrong?
thanks

[pete_bisby]

You either need to set you database connection within your class, or pass the database connection as a parameter into your function:

function Field($dbConn, $customer, $name) {
...

[nephish]

well ok then, easy enough.
thanks for your help