You can refer to this link for your solution,
there I have explained how to solve it,
Let me know if you have any issues.
Hope it helps !
Several ways to do this. If you only want to Show the BMS objects that are related to the project of the create button you can do one of the following things for example:
1. Connect the Arbeitsfolge directly to the project. In that case in your drop-down you can use the datasource xpath and the constrain by function to filter the data to only show BMS objects that are related to the project that is related to the arbeitsfolge.(https://docs.mendix.com/refguide7/reference-selector/)
2. You can use a datasource microflow to filter out the correct BMS objects. Note that for this you either need a page parameter of the project object or you need to connect arbeitsfolge directly to the project as well.
Hope this helps!
Thanks for the answer.
I actually don't want to change the Domain Model, because of the original Hirachie of the Real Model. So a project has x "BMS" which has x "Work Sequences" which in turn has x "Robot".
I think the second point will work for me, but i am not sure how to get the Page Parameter of the Project to the Creation Screen of “Arbeitsfolge”