Internals
---------

The internals of ``gt-jdbc`` layout the code for ``JDBCDataStore`` and abstract classes that are extended for each new format.

Related:

* :doc:`gt-main internal <../data/internal/>`

JDBCDataStore
^^^^^^^^^^^^^

The ``JDBCDataStore`` class is an extension of ``ContentDataStore`` defined by ``gt-main``.

.. image:: /images/content2.PNG

``ContentDataStore`` is extended with a concrete ``JDBCDataStore`` that:

* delegates out to a ``SQLDialect`` that is implemented for each format
* makes use of custom extensions for:
  
  * ``JDBCState``
  * ``JDBCFeatureSource`` supported by a feature reader that makes use of
    a light-weight feature implementation
  * ``JDBCFeatureStore`` supported by two feature writer implementations


.. image:: /images/jdbcDataStore.PNG

You will find a careful attention to details and steps taken to minimize any duplication of code. The ``FeatureStore`` implementation maintains an internal delegate ``JDBCFeatureSource`` in order to smoothly handle ``getFeature()`` requests without duplicating code.

SQLDialect
^^^^^^^^^^

If you would like to implement support for an additional format please ask on the developers list. The clearest starting place is to review the *``gt-jdbc-h2``* code which serves as the reference implementation.

To have your format accepted by GeoTools you will also need to extend the
conformance test cases as shown in the *``gt-jdbc-h2``* module. 

Here is a brief illustration of ``SQLDialect`` as implemented by the ``gt-jdbc-h2`` plugin.


.. image:: /images/jdbcDataStoreH2.PNG

As expected this class is required to fill in the H2 specific details:

* how to decode and encode Geometry and Bounds information
* handle database specific functionality such as sequences
* follow up to table creation (often needed if geometry columns need to be registered)

Your implementation of these methods may depend on the conventions of your database.  Oracle spatial for example will have its own idea on how to handle SRID values, while a simple Java database like H2 will make use of the GeoTools CRS class.