Merge ~pappacena/launchpad:comment-editing-db-patch into launchpad:db-devel

[Thiago F. Pappacena]

Database patch for comment editing feature

[Colin Watson (cjwatson)]

review: Needs Information

[Thiago F. Pappacena (pappacena)]

Pushed the requested changes. It worth another review round.

[Colin Watson (cjwatson)]

review: Approve

[Colin Watson (cjwatson)]

Requested a second DB review from William.

[William Grant (wgrant)]

Thanks, just a couple comments.

review: Approve (db)

[Thiago F. Pappacena (pappacena)]

Pushed the requested changes. This should be ready to be merged now.

diff --git a/database/schema/patch-2210-31-0.sql b/database/schema/patch-2210-31-0.sql
 new file mode 100644
index 0000000..8c11aac
--- /dev/null
+++ b/database/schema/patch-2210-31-0.sql
@@ -0,0 +1,50 @@
+-- Copyright 2021 Canonical Ltd.  This software is licensed under the
+-- GNU Affero General Public License version 3 (see the file LICENSE).
+
+SET client_min_messages=ERROR;
+
+ALTER TABLE Message
+    ADD COLUMN date_deleted timestamp without time zone,
+    ADD COLUMN date_last_edited timestamp without time zone;
+
+CREATE TABLE MessageRevision (
+    id serial PRIMARY KEY,
+    message integer NOT NULL REFERENCES Message,
+    revision integer NOT NULL,
+    subject text,
+    date_created timestamp without time zone NOT NULL,
+    date_deleted timestamp without time zone
+) WITH (fillfactor='100');
+
+CREATE UNIQUE INDEX messagerevision__message__revision__key
+    ON MessageRevision(message, revision);
+
+COMMENT ON TABLE MessageRevision IS 'Old versions of an edited Message';
+COMMENT ON COLUMN MessageRevision.message
+    IS 'The current message of this revision';
+COMMENT ON COLUMN MessageRevision.revision
+    IS 'The revision monotonic increasing number';
+COMMENT ON COLUMN MessageRevision.date_created
+    IS 'When the original message was edited and created this revision';
+COMMENT ON COLUMN MessageRevision.date_deleted
+    IS 'If this revision was deleted, when did that happen';
+
+
+CREATE TABLE MessageRevisionChunk (
+    id serial PRIMARY KEY,
+    messagerevision integer NOT NULL REFERENCES MessageRevision,
+    sequence integer NOT NULL,
+    content text NOT NULL
+) WITH (fillfactor='100');
+
+CREATE UNIQUE INDEX messagerevisionchunk__messagerevision__sequence__key
+    ON MessageRevisionChunk(messagerevision, sequence);
+
+COMMENT ON TABLE MessageRevisionChunk
+    IS 'Old chunks of a message when a revision was created for it';
+COMMENT ON COLUMN MessageRevisionChunk.sequence
+    IS 'Order of this particular chunk';
+COMMENT ON COLUMN MessageRevisionChunk.content
+    IS 'Text content for this chunk of the message.';
+
+INSERT INTO LaunchpadDatabaseRevision VALUES (2210, 31, 0);