A one to one relation is when a model relates to one, and only one, other models. An example of such a relation would be that a Person model has one Government ID, and a Government ID can belong to one, and only one, Person. In this relation, both models have only one reference to each other, and no more. In Vapor, this type of relation is known as a Parent/Child relation. The database table for such a relation would look like this:
Persons:
| Column Name | Column Type |
| id | Identifier |
| name | String |
government_ids:
| Column Name | Column Type |
| id | Identifier |
| number | Int |
| person_id | Identifier (Foreign Key) |
The following is how we would express this relation in our two model classes:
extension GovernmentId ...
