MySQL Workbench - Creating a one-to-one relationship using existing columns? How do I create a one-to-one relationship using existing columns in MySQL Workbench?

I have an EER diagram tab open and I am selecting from the toolbar on the left hand side.

Unfortunately it seems that I can create a one-to-many or many-to-one relationship but not a one-to-one.
Right click on the relationship line
Select 'Edit Relationship'
Click on the Foreign Key tab in the Relationship Tab
The Cardinality of the relationship can be changed with the two radio buttons