Inheritance
===========

.. _joined-table-inheritance-example:

Joined Table
------------

SQLAlchemy includes a feature where a model class hierarchy is implemented by
giving each class it's own table. For example, an :samp:`Employee` might have
an :samp:`id`, :samp:`name` and :samp:`type`. Then a :samp:`Manager` model
might be defined that derives from :samp:`Employee` and adds the
:samp:`manager_data` column.

.. seealso::

    :ref:`joined-table-inheritance`
      OpenAlchemy documentation for joined table inheritance.

    `SQLAlchemy joined table inheritance documentation <https://docs.sqlalchemy.org/en/13/orm/inheritance.html#joined-table-inheritance>`_
      Documentation for SQLAlchemy joined table inheritance.

The following example defines joined tabled inheritance where :samp:`Employee`
is the parent and :samp:`Manager` and :samp:`Engineer` derive from it:

.. literalinclude:: ../../../examples/inheritance/joined-example-spec.yml
    :language: yaml
    :linenos:

The following file uses OpenAlchemy to generate the SQLAlchemy models:

.. literalinclude:: ../../../examples/inheritance/joined_models.py
    :language: python
    :linenos:

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

.. literalinclude:: ../../../examples/inheritance/joined_models_traditional.py
    :language: python
    :linenos:

OpenAlchemy will generate the following typed models:

.. literalinclude:: ../../../examples/inheritance/joined_models_auto.py
    :language: python
    :linenos:

.. _single-table-inheritance-example:

Single Table
------------

Single table inheritance is very similar to :ref:`joined-table-inheritance`
with the difference that all classes are linked to the same table and there is
no foreign key relationship between the models.

.. seealso::

    :ref:`single-table-inheritance`
      OpenAlchemy documentation for single table inheritance.

    `SQLAlchemy single table inheritance documentation <https://docs.sqlalchemy.org/en/13/orm/inheritance.html#single-table-inheritance>`_
      Documentation for SQLAlchemy single table inheritance.

The following example defines single tabled inheritance where :samp:`Employee`
is the parent and :samp:`Manager` and :samp:`Engineer` derive from it:

.. literalinclude:: ../../../examples/inheritance/single-example-spec.yml
    :language: yaml
    :linenos:

The following file uses OpenAlchemy to generate the SQLAlchemy models:

.. literalinclude:: ../../../examples/inheritance/single_models.py
    :language: python
    :linenos:

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

.. literalinclude:: ../../../examples/inheritance/single_models_traditional.py
    :language: python
    :linenos:

OpenAlchemy will generate the following typed models:

.. literalinclude:: ../../../examples/inheritance/single_models_auto.py
    :language: python
    :linenos:

.. seealso::
    :ref:`getting-started`