Add WIP example of database usage in bot

examples/database/databasebot.py

@@ -0,0 +1,39 @@
+from typing import Type
+
+from sqlalchemy import Column, String, Text, Table, MetaData, orm, func
+
+from mautrix.types import EventType
+from maubot import Plugin, MessageEvent
+from maubot.handlers import event, command
+
+
+class DatabaseBot(Plugin):
+    db: orm.Session
+    events: Type[Table]
+
+    async def start(self) -> None:
+        await super().start()
+
+        db_factory = orm.sessionmaker(bind=self.database)
+        self.db = orm.scoped_session(db_factory)
+        table_meta = MetaData(bind=self.db)
+        self.events = Table("event", table_meta,
+                            Column("room_id", String(255), primary_key=True),
+                            Column("event_id", String(255), primary_key=True),
+                            Column("sender", String(255)),
+                            Column("body", Text))
+        # In the future, there will be a proper way to include Alembic upgrades in plugins.
+        table_meta.create_all()
+
+    @event.on(EventType.ROOM_MESSAGE)
+    async def handler(self, event: MessageEvent) -> None:
+        self.db.add(self.events(room_id=event.room_id, event_id=event.event_id,
+                                sender=event.sender, body=event.content.body))
+
+    @command.new("stats")
+    async def find(self, _: MessageEvent) -> None:
+        res = (self.db
+               .query(func.sum(self.events.event_id))
+               .group_by(self.events.room_id, self.events.sender)
+               .all())
+        print(res)