This isn’t possible in Mendix. If you want a one-to-one relationship between entities, then both have to be persistent.
As the other commented suggested, you cannot. But assuming you’re trying to access the relationship from the NPE side, there’s really not much difference in functionality.
If you’re trying to access it from the other side, I would reconsider your domain model a bit more.
Hi, Esequiel Alfaro
Its not possible to have one to one relationship between non-persistable and persistable, you can do one to many or many to many where many side should be on non persistable side (An association between a persistable entity and a non-persistable entity must start in the non-persistable entity and have owner 'Default'.)
and for more understanding why it is not possible (one to one) you can check below answer link.
Just use a one to many relationship and use the Head function to get the first.