From deec2cf578ce1c898bcde88117610d8bc945f174 Mon Sep 17 00:00:00 2001
From: Sam Saffron <sam.saffron@gmail.com>
Date: Fri, 8 Nov 2019 11:44:02 +1100
Subject: [PATCH] FIX: drafts are unique by draft_key and user_id

Previously our index was non unique, causing situations where a user could
have multiple drafts stored in the table for the same exact entity.

This does not properly reflect reality and needed to change as in certain
cases duplicate drafts could be created causing internal data inconsistency
---
 app/models/draft.rb                           |  2 +-
 ...191108000414_add_unique_index_to_drafts.rb | 27 +++++++++++++++++++
 2 files changed, 28 insertions(+), 1 deletion(-)
 create mode 100644 db/migrate/20191108000414_add_unique_index_to_drafts.rb

diff --git a/app/models/draft.rb b/app/models/draft.rb
index 2bbc3bcaf66..4f7a03711f3 100644
--- a/app/models/draft.rb
+++ b/app/models/draft.rb
@@ -282,5 +282,5 @@ end
 #
 # Indexes
 #
-#  index_drafts_on_user_id_and_draft_key  (user_id,draft_key)
+#  index_drafts_on_user_id_and_draft_key  (user_id,draft_key) UNIQUE
 #
diff --git a/db/migrate/20191108000414_add_unique_index_to_drafts.rb b/db/migrate/20191108000414_add_unique_index_to_drafts.rb
new file mode 100644
index 00000000000..f50d1b7c49d
--- /dev/null
+++ b/db/migrate/20191108000414_add_unique_index_to_drafts.rb
@@ -0,0 +1,27 @@
+# frozen_string_literal: true
+
+class AddUniqueIndexToDrafts < ActiveRecord::Migration[6.0]
+  def up
+
+    execute <<~SQL
+      DELETE FROM drafts d1
+      USING (
+        SELECT MAX(id) as id, draft_key, user_id
+        FROM drafts
+        GROUP BY draft_key, user_id
+        HAVING COUNT(*) > 1
+      ) d2
+      WHERE
+        d1.draft_key = d2.draft_key AND
+        d1.user_id = d2.user_id AND
+        d1.id <> d2.id
+    SQL
+
+    remove_index :drafts, [:user_id, :draft_key]
+    add_index :drafts, [:user_id, :draft_key], unique: true
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration
+  end
+end