I figured out that you can easily solve this by adding a rule/condition for GroupBox or DataView visibility. This way I simply hide the Details part on my form when the Master part was not saved/committed.
I added:
isNew($currentObject) = false
Now when a new master object is being created, it is not possible to create new detail records until the Save button was pressed first.
Some background / context info…
The master/detail form (NewEdit of the newsletterissue):
The conditional visibility for my GroubBox containing Detail grid:
The only limitation of this solution is that it is not possible for the user to add Detail objects when the Master object is not saved. This will require the user to Edit the Master object after saving.
The result….
When creating a Newsletter Issue, the Detail objects (Topics in this case) are not available for adding:
When opening the Newsletter Issue for Edit, the Detail grid is shown and the CRUD operations are available: