Field valuw on a record-row

var myvariable = row.getFieldValue("main_ID");

hi

you don't say what you are trying to do,

If your operation is on a field level - you can do it through the field'd custom display

Otherwise use the list page: Before record processed
hope it helps,

In the php-codesnippet I want to do some different actions with the value of main_ID (check on a other table, check on other field valies, etc) and echo the result on that same row.

I can do it with a home-made function through the custom display but I thought there is purhaps a much more easy way to do it.

The best approach is to use 'View as' Custom instead of the code snippet. This way you handle both display part and easy access to record values.

https://xlinesoft.com/phprunner/docs/view_as_settings_custom.htm

As it happens, I just needed to do similar in one of my projects...
I have a customer table and I wanted to show the customers boat name along with the customer ID.

I tried to do it with the mouseover event but couldn't get it to work so I used custom view...
In the customer table I used custom view for the account_id field, and searched the boat table for the customers boat name.
account_id is the field name in the customers table, and a similar linked field in the boat table.
This field now shows the original customers account_id and underneath the customers boat name in parenthesis ()
Here's the code...
global $dal;

$acc_id = $data["account_id"];

$sql = "select * from boat where account_id = '$acc_id'";

$rs = CustomQuery($sql);

$bdata = db_fetch_array($rs);

$value = $acc_id . "
(" . $bdata["boatname"] . ")";