I'm kinda new to Mendix, but already I've run into this problem multiple times: I want to filter a list by association. Right now you can only filter by fixed data (strings, ints, decimals, booleans). I can't retrieve an object from a list based on the same object association.
For example: I have activities that log hours spent on a project. Now I want to generate a table with hours spent this week and last week per project, but I only want to show the projects that have activities in this period. So I'd like to retrieve all hours from this and last week, loop through them and add (or update) the project to the list. But in this loop I need to check if the project is already present in the list, so I can update it. I know I can do this the other way around (create a list of projects, loop through them to get the activities and if there are none, delete it, but that is much more overhead)
Please let me know if this would be possible, or if I'm approaching my problem the wrong way.