I'd like to extend a related list with a column that does not directly live on the related module, but on a grandchild (a field from products, that I want to show in a related list for assets). Can I use a workflow expression in the ListColumns business map?
No, business maps can't go down that path because they don't modify the SQL to actually join on the grandchild table
To do this, I think you have to modify the $related_tables property in the module
https://github.com/tsolucio/corebos/blob/master/vtlib/ModuleDir/ModuleFile.php#L33
at least that would be the first thing I would try, and if that doesn't work then just create yourself a custom related list handler method that constructs the SQL you need
OK, will do. Been meaning to talk to you about related lists enhancement / master detail stuff but just been really swamped lately.