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db: add some PullRequest.query() shortcuts
This makes database query code more explicit and increases readability.
E.g. the function name get_pullrequest_cnt_for_user was bad, because the
concept of "pullrequest for user" is incredibly vague, and could refer
to any kind of association between PRs and users. (Quiz time! Does it
mean that the user is the PR owner, that the user is reviewing, or that
the user has commented on the PR and thus is receiving notifications?)
A descriptive name could be "get_open_pull_request_count_for_reviewer",
because the function is indeed only concerned with reviewers and only
with open pull requests. But at this point, we might as well say
PullRequest.query(reviewer_id=user, include_closed=False).count()
which is only slightly longer, and doesn't require us to write dozens
of little wrapper functions (including, any moment now, a separate
function for listing the PRs instead of counting them).
Note that we're not actually going down an abstraction level by doing
this. We're still operating on the concepts of "pull request", "open"
and "reviewer", and are not leaking database implementation details.
The query() shortcuts are designed so they default to not altering
the query. Any processing requires explicit opt-in by the caller.
This makes database query code more explicit and increases readability.
E.g. the function name get_pullrequest_cnt_for_user was bad, because the
concept of "pullrequest for user" is incredibly vague, and could refer
to any kind of association between PRs and users. (Quiz time! Does it
mean that the user is the PR owner, that the user is reviewing, or that
the user has commented on the PR and thus is receiving notifications?)
A descriptive name could be "get_open_pull_request_count_for_reviewer",
because the function is indeed only concerned with reviewers and only
with open pull requests. But at this point, we might as well say
PullRequest.query(reviewer_id=user, include_closed=False).count()
which is only slightly longer, and doesn't require us to write dozens
of little wrapper functions (including, any moment now, a separate
function for listing the PRs instead of counting them).
Note that we're not actually going down an abstraction level by doing
this. We're still operating on the concepts of "pull request", "open"
and "reviewer", and are not leaking database implementation details.
The query() shortcuts are designed so they default to not altering
the query. Any processing requires explicit opt-in by the caller.
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Database schema changes
=======================
Kallithea uses Alembic for :ref:`database migrations <upgrade_db>`
(upgrades and downgrades).
If you are developing a Kallithea feature that requires database schema
changes, you should make a matching Alembic database migration script:
1. :ref:`Create a Kallithea configuration and database <setup>` for testing
the migration script, or use existing ``development.ini`` setup.
Ensure that this database is up to date with the latest database
schema *before* the changes you're currently developing. (Do not
create the database while your new schema changes are applied.)
2. Create a separate throwaway configuration for iterating on the actual
database changes::
paster make-config Kallithea temp.ini
Edit the file to change database settings. SQLite is typically fine,
but make sure to change the path to e.g. ``temp.db``, to avoid
clobbering any existing database file.
3. Make your code changes (including database schema changes in ``db.py``).
4. After every database schema change, recreate the throwaway database
to test the changes::
rm temp.db
paster setup-db temp.ini --repos=/var/repos --user=doe --email doe@example.com --password=123456 --no-public-access --force-yes
paster repo-scan temp.ini
5. Once satisfied with the schema changes, auto-generate a draft Alembic
script using the development database that has *not* been upgraded.
(The generated script will upgrade the database to match the code.)
::
alembic -c development.ini revision -m "area: add cool feature" --autogenerate
6. Edit the script to clean it up and fix any problems.
Note that for changes that simply add columns, it may be appropriate
to not remove them in the downgrade script (and instead do nothing),
to avoid the loss of data. Unknown columns will simply be ignored by
Kallithea versions predating your changes.
7. Run ``alembic -c development.ini upgrade head`` to apply changes to
the (non-throwaway) database, and test the upgrade script. Also test
downgrades.
The included ``development.ini`` has full SQL logging enabled. If
you're using another configuration file, you may want to enable it
by setting ``level = DEBUG`` in section ``[handler_console_sql]``.
The Alembic migration script should be committed in the same revision as
the database schema (``db.py``) changes.
See the `Alembic documentation`__ for more information, in particular
the tutorial and the section about auto-generating migration scripts.
.. __: http://alembic.zzzcomputing.com/en/latest/
Troubleshooting
---------------
* If ``alembic --autogenerate`` responds "Target database is not up to
date", you need to either first use Alembic to upgrade the database
to the most recent version (before your changes), or recreate the
database from scratch (without your schema changes applied).
|