One to One
==========

A one to one relationship associates one child with one parent and vice-versa.
For example, the pay information for an employee may be stored in a different
table than the employee. However, one employee can only be paid in one way
and each employee must be paid separately.

.. seealso::

    :ref:`one-to-one`
      OpenAlchemy documentation for one to one relationships.

    `SQLAlchemy One to One <https://docs.sqlalchemy.org/en/13/orm/basic_relationships.html#one-to-one>`_
      SQLAlchemy documentation for one to one relationships.

The following example defines a one to one relationship between *Employee*
and *PayInfo*:

.. literalinclude:: ../../../../examples/relationship/one_to_one/example-spec.yml
    :language: yaml
    :linenos:

The following file uses OpenAlchemy to generate the SQLAlchemy models:

.. literalinclude:: ../../../../examples/relationship/one_to_one/models.py
    :language: python
    :linenos:

The SQLAlchemy models generated by OpenAlchemy are equivalent to the following
traditional models file:

.. literalinclude:: ../../../../examples/relationship/one_to_one/models_traditional.py
    :language: python
    :linenos:

OpenAlchemy will generate the following typed models:

.. literalinclude:: ../../../../examples/relationship/one_to_one/models_auto.py
    :language: python
    :linenos: