db: add methods for values associated with a plugin

[deathbybandaid]

This aims to resolve issue #1501.

The one thing I was uncertain of is if we need to bother using .lower() like we do with channels.

---

@dgw edit: Closes #1501

[deathbybandaid]

and depending on PR #1526 , I took the liberty of writing this snippet in advance for consistency. I was not sure if I should include it here, there, or wait until this, and #1526 are merged first.

def delete_plugin_value(self, plugin, key):
        """Deletes the value for a given key to be associated with the plugin."""
        plugin = Identifier(plugin).lower()
        session = self.ssession()
        try:
            result = session.query(PluginValues) \
                .filter(PluginValues.plugin == plugin)\
                .filter(PluginValues.key == key) \
                .one_or_none()
            # PluginValues exists, update
            if result:
                session.delete(result)
                session.commit()
        except SQLAlchemyError:
            session.rollback()
            raise
        finally:
            session.close()

[deathbybandaid]

another other concern is if Identifier() even needs to be used here.

[deathbybandaid]

Just dropping another note: should probably add to test_db.py

[dgw]

In brief:

• Good start! Exciting to have an implementation of this.
• Using .lower() on the plugin name is probably good for consistency, yes.
• Casting the plugin name to Identifier is almost certainly unnecessary (it isn't one).
• Pretend db: add methods to delete a channel or nick's key from database #1526 will be merged before this (because it probably will be) and include a delete_plugin_value method in this PR.
• Adding tests is always valuable—always!
  • Per your IRC comments on this: As far as using sqlite directly goes, rewriting the DB tests to use SQLAlchemy instead is for a separate PR, and for this PR you should mimic the existing ones. (Opening a PR to switch the DB tests yourself is welcome of course!)

Longer thoughts:

Lacking any reasonable ideas for making the plugin argument optional (auto-detecting the calling module from within the db functions would require some possibly fragile introspection), I'll refrain from asking about that. I would love to have e.g. bot.db.set_plugin_value('key', True) "just work" without having to re-specify the plugin name, but… concerns about compatibility with alternative Python implementations and non-Linux platforms make me think doing so would be far more complicated than it's worth.

Besides, the existing set/get functions already require passing the nickname or channel, so the way this works now is parallel to how those work anyway. (Yes, I have thought about making the channel-value methods "automatic", too. Not worth it either, lol.)

[deathbybandaid]

Identifier removed, lower() retained, tests added, squashed

[deathbybandaid]

plugin names are not channels

[deathbybandaid]

as per PR #1652 this has been updated

[dgw]

Same consistency tweaks as #1526, as a start.

[dgw]

Just a few last consistency tweaks to docstrings/comments and we're done!

[dgw]

Updated. Enjoy your trip, @deathbybandaid! (Well, as much as you can enjoy a work trip. 😼)