Xataface Forums

What is the best way to pre-populate a new record form with a calculated value based on the previous record or a maximum value from all records? For example, when tracking automobile mileage, rather than starting from scratch with each new record, I would like to prefill the new odometer value with the previous odometer value plus the trip miles. Or, when generating invoice numbers, work order numbers, etc. I would prefill the new value with the maximum existing value plus one. I can't use an auto-incremement field for this because it is not the primary key, and MySQL only allows one per table.

Thanks,
Alan

Alan,

You need to calculate your value in the delegate class of the table with the function fieldname__default
http://xataface.com/wiki/Delegate_class_methods

Jean

Thanks Jean,

I am somewhat familiar with the fieldname__default function. I actually created that wiki page.

But I am not sure how to use the result of an SQL query with this function, specifically to retrieve the value from a previous record or the MAX() value from all previous records. Can someone provide an example of how to do this?

Thanks,
Alan

Well you can have something like this :

Code: Select all

    $this->app =& Dataface_Application::getInstance();

        $result = mysql_query("select MAX(field_name) AS maximum from Table", $this->app->db());
       

            while($row = mysql_fetch_assoc($result))
            {
                return $row['maximum'];
            }

That's perfect! Thank you!

Alan