Optimize Drafts retrieval

This adds a database index to speed up retrieval of Drafts.

It is untested with SQLite.

migrations/migrations.go

@@ -63,6 +63,7 @@ var migrations = []Migration{
 	New("support slack oauth", oauthSlack),                          // V4 -> v5
 	New("support ActivityPub mentions", supportActivityPubMentions), // V5 -> V6
 	New("support oauth attach", oauthAttach),                        // V6 -> V7 (v0.12.0)
+	New("optimize drafts retrieval", optimizeDrafts),                // V7 -> V8
 }
 
 // CurrentVer returns the current migration version the application is on

migrations/v8.go

@@ -0,0 +1,29 @@
+/*
+ * Copyright © 2020 A Bunch Tell LLC.
+ *
+ * This file is part of WriteFreely.
+ *
+ * WriteFreely is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License, included
+ * in the LICENSE file in this source code package.
+ */
+
+package migrations
+
+func optimizeDrafts(db *datastore) error {
+	t, err := db.Begin()
+
+	_, err = t.Exec(`ALTER TABLE posts ADD INDEX(owner_id, id)`)
+	if err != nil {
+		t.Rollback()
+		return err
+	}
+
+	err = t.Commit()
+	if err != nil {
+		t.Rollback()
+		return err
+	}
+
+	return nil
+}