DEV: Delete upload references on draft cleanup (#26877)

In #22851 we added a dependent strategy for deleting upload references when a draft is destroyed. This, however, didn't catch all cases, because we still have some code that issues DELETE drafts queries directly to the database. Specifically in the weekly cleanup job handled by Draft#cleanup!.

This PR fixes that by turning the raw query into an ActiveRecord #destroy_all, which will invoke the dependent strategy that ultimately deletes the upload references. It also includes a post migration to clear orphaned upload references that are already in the database.

app/models/draft.rb

@@ -237,19 +237,18 @@ class Draft < ActiveRecord::Base
   end
 
   def self.cleanup!
-    DB.exec(<<~SQL)
-      DELETE FROM drafts
-       WHERE sequence < (
+    Draft.where(<<~SQL).in_batches(of: 100).destroy_all
+      sequence < (
         SELECT MAX(s.sequence)
           FROM draft_sequences s
-         WHERE s.draft_key = drafts.draft_key
-           AND s.user_id = drafts.user_id
+          WHERE s.draft_key = drafts.draft_key
+          AND s.user_id = drafts.user_id
       )
     SQL
 
     # remove old drafts
     delete_drafts_older_than_n_days = SiteSetting.delete_drafts_older_than_n_days.days.ago
-    Draft.where("updated_at < ?", delete_drafts_older_than_n_days).destroy_all
+    Draft.where("updated_at < ?", delete_drafts_older_than_n_days).in_batches(of: 100).destroy_all
 
     UserStat.update_draft_count
   end

db/post_migrate/20240506035024_clear_orphaned_draft_upload_references.rb

@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+
+class ClearOrphanedDraftUploadReferences < ActiveRecord::Migration[7.0]
+  def up
+    execute <<~SQL
+      DELETE
+      FROM
+        "upload_references"
+      WHERE
+        "upload_references"."target_type" = 'Draft' AND
+        "upload_references"."target_id" NOT IN (
+          SELECT "drafts"."id" FROM "drafts"
+        )
+    SQL
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration
+  end
+end

spec/models/draft_spec.rb

@@ -133,6 +133,7 @@ RSpec.describe Draft do
     key = Draft::NEW_TOPIC
 
     Draft.set(user, key, 0, "draft")
+
     Draft.cleanup!
     expect(Draft.count).to eq 1
     expect(user.user_stat.draft_count).to eq(1)
@@ -142,10 +143,16 @@ RSpec.describe Draft do
     Draft.set(user, key, seq, "draft")
     DraftSequence.update_all("sequence = sequence + 1")
 
+    draft = Draft.first
+    draft.upload_references << UploadReference.create!(target: draft, upload: Fabricate(:upload))
+
+    expect(UploadReference.count).to eq(1)
+
     Draft.cleanup!
 
     expect(Draft.count).to eq 0
     expect(user.reload.user_stat.draft_count).to eq(0)
+    expect(UploadReference.count).to eq(0)
 
     Draft.set(Fabricate(:user), Draft::NEW_TOPIC, 0, "draft")