Add migration to prune previous ticket self-mentions

todosrht/alembic/versions/074182407bb2_remove_self-referencing_ticket_mention_events.py

@@ -0,0 +1,30 @@
+"""Remove self-referencing ticket mention events
+
+Revision ID: 074182407bb2
+Revises: 61e241dc978c
+Create Date: 2020-08-21 18:25:15.512581
+
+"""
+
+# revision identifiers, used by Alembic.
+revision = '074182407bb2'
+down_revision = '61e241dc978c'
+
+from alembic import op
+from todosrht.types import Event, EventType
+from sqlalchemy.orm import sessionmaker
+
+
+Session = sessionmaker()
+
+
+def upgrade():
+    bind = op.get_bind()
+    session = Session(bind=bind)
+    (session.query(Event)
+        .filter(Event.event_type == EventType.ticket_mentioned)
+        .filter(Event.from_ticket_id == Event.ticket_id)).delete()
+
+
+def downgrade():
+    pass