Merge branch 'sh-fix-mysql-migration-10-3' into 'master'

Fix migration for removing orphaned issues.moved_to_id values in MySQL and PostgreSQL

Closes #41498

See merge request gitlab-org/gitlab-ce!16141

changelogs/unreleased/sh-fix-mysql-migration-10-3.yml

+---
+title: Fix migration for removing orphaned issues.moved_to_id values in MySQL and PostgreSQL
+merge_request:
+author:
+type: fixed

db/migrate/20171106151218_issues_moved_to_id_foreign_key.rb

@@ -15,8 +15,20 @@ class IssuesMovedToIdForeignKey < ActiveRecord::Migration
     self.table_name = 'issues'
 
     def self.with_orphaned_moved_to_issues
-      where('NOT EXISTS (SELECT true FROM issues WHERE issues.id = issues.moved_to_id)')
-        .where('moved_to_id IS NOT NULL')
+      if Gitlab::Database.postgresql?
+        # Be careful to use a second table here for comparison otherwise we'll null
+        # out all rows that don't have id == moved.to_id!
+        where('NOT EXISTS (SELECT true FROM issues B WHERE issues.moved_to_id = B.id)')
+          .where('moved_to_id IS NOT NULL')
+      else
+        # MySQL doesn't allow modification of the same table in a subquery,
+        # and using a temporary table isn't automatically guaranteed to work
+        # due to the MySQL query optimizer. See
+        # https://dev.mysql.com/doc/refman/5.7/en/update.html for more
+        # details.
+        joins('LEFT JOIN issues AS b ON issues.moved_to_id = b.id')
+          .where('issues.moved_to_id IS NOT NULL AND b.id IS NULL')
+      end
     end
   end
 

spec/migrations/issues_moved_to_id_foreign_key_spec.rb

+require 'spec_helper'
+require Rails.root.join('db', 'migrate', '20171106151218_issues_moved_to_id_foreign_key.rb')
+
+# The schema version has to be far enough in advance to have the
+# only_mirror_protected_branches column in the projects table to create a
+# project via FactoryBot.
+describe IssuesMovedToIdForeignKey, :migration, schema: 20171114150259 do
+  let!(:issue_first) { create(:issue, moved_to_id: issue_second.id) }
+  let!(:issue_second) { create(:issue, moved_to_id: issue_third.id) }
+  let!(:issue_third) { create(:issue) }
+
+  subject { described_class.new }
+
+  it 'removes the orphaned moved_to_id' do
+    subject.down
+
+    issue_third.update_attributes(moved_to_id: 100000)
+
+    subject.up
+
+    expect(issue_first.reload.moved_to_id).to eq(issue_second.id)
+    expect(issue_second.reload.moved_to_id).to eq(issue_third.id)
+    expect(issue_third.reload.moved_to_id).to be_nil
+  end
+end