Hi Marcel,
To check if the object already exists in your local database (to avoid duplicates), you could use one of the List Operations.
You first need to retrieve all the objects from your local database to get a List of objects, and then you could either use the List Operation “Contains” or “Find”, to search for possible duplications. If no match is found then it means that the object is not a duplicate and you can proceed, otherwise you would display your message of duplicate was found.
I hope that helps you with your question, best regards!