Hi Gal,
Since the Fullname is a calculated attribute, it will keep updating whenever the object is loaded on the page.
In short, a calculated attribute will be updated whenever the object is created, retrieved, or loaded on the page.
For your use case, please convert the calculated attribute to a stored attribute. Before committing your reservation object, you can update the Fullname of that object by setting it to the current user's name
Hi Gal Verlic,
Related to your question, but not answering it since stella already did;
Looks like you didn't take the Rapid developer course online.
That will help you a lot to start with Mendix.
Next to that, for these kind of actions, use microflows instead. These are more secure and you committing to the database anyways. So performance isn't affected.