Upgrade a database

For changes to the database schema, we rely on `Alembic <http://alembic.readthedocs.org/>`_.
This allows us to do upgrade and downgrade of schema migration, kind of like
one would do commits in a system like git.

To upgrade the database to the latest version simply run:

    alembic upgrade head

.. note:: if pagure's configuration file isn't in ``/etc/pagure/pagure.cfg``
        you will have to specify it to alembic using the command: ::

            PAGURE_CONFIG=/path/to/pagure.cfg alembic upgrade head

        This allow applies for the command specified below.

This may fail for different reasons:

* The change was already made in the database

This can be because the version of the database schema saved is incorrect.
It can be debugged using the following commands:

  * Find the current revision: ::

        alembic current

  * See the entire history: ::

        alembic history

Once the revision at which your database should be is found (in the history)
you can declare that your database is at this given revision using: ::

    alembic stamp <revision id>

Eventually, if you do not know where your database is or should be, you can
do an iterative process stamping the database for every revision, one by one
trying every time to ``alembic upgrade`` until it works.

* The database used does not support some of the changes

SQLite is handy for development but does not support all the features of a
real database server. Upgrading a SQLite database might therefore not work,
depending on the changes done.

In some cases, if you are using a SQLite database, you will have to destroy
it and create a new one.