Something's wrong here.
Presentation :belongs_to user means that Presentation has a column
called user_id which 'points to' a User. You dont have this.
And belongs_to isn't symmetrical, the other end needs a :has_many, or
From what you started out saying there's one presentation for each
user, in which case the relations would be:
with user_id field in the presentations table.
That said, has_one is almost never used like this, if there really is
a fixed one-one relationship between presentations and users then they
probably should be combined in one table. If, on the other hand, the
situation is that the User can have multiple presentations then you
might want something like:
has_one :current_presentation, :order => "updated_at DESC"
where the current_presentation uses the magic updated_at field to get
the most recently modified presentation.