One-to-One Unidirectional Relationships 

The one-to-one unidirectional relationship differs from the one-to-one bidirectional relationships by the missing field of persistent capable class type on either of the sides.

In the relational model, the foreign key must be in the table that is mapped to the class with the field of persistence capable class type.

The mapping metadata for the remaining field of persistent capable class type is the same as the mapping in the one-to-one bidirectional case, except that the property update in the relationship field must not be set to false.