The DocentVakGroup is the key here. See the example microflow here:
Pass the DocentVakGroup object you want to check to this microflow. Retrieve the other three objects first. Then the key part to retrieve other DocentVakGroup objects with references to the same other objects.
Do a retrieve of DocentVakGroup with something like the following XPath constrained
[id != $DocentVakGroup]
[MyFirstModule.DocentVakGroup_Klas/MyFirstModule.Klas/Naam = $Klas/Naam]
[MyFirstModule.DocentVakGroup_ActiefDocent/MyFirstModule.Docent/Achternaam = $Docent/Achternaam]
[MyFirstModule.DocentVakGroup_Vak/MyFirstModule.Vak/Naam = $Vak/Naam]
The first line makes sure that you do not retrieve the same object as the object you want to check.
Do note that you want to make this check on unique stuff. If you have more teachers with the same name you are in trouble. But you probably get the meaning. If this retrieve is empty create the object otherwise give a message that the combination already exist.
Regards,
Ronald
And the res