gitlab-org--gitlab-foss/db/migrate/20140416074002_add_index_on_iid.rb

class AddIndexOnIid < ActiveRecord::Migration
  def change
    RemoveDuplicateIid.clean(Issue)
    RemoveDuplicateIid.clean(MergeRequest, 'target_project_id')
    RemoveDuplicateIid.clean(Milestone)

    add_index :issues, [:project_id, :iid], unique: true
    add_index :merge_requests, [:target_project_id, :iid], unique: true
    add_index :milestones, [:project_id, :iid], unique: true
  end
end

class RemoveDuplicateIid
  def self.clean(klass, project_field = 'project_id')
    duplicates = klass.find_by_sql("SELECT iid, #{project_field} FROM #{klass.table_name} GROUP BY #{project_field}, iid HAVING COUNT(*) > 1")

    duplicates.each do |duplicate|
      project_id = duplicate.send(project_field)
      iid = duplicate.iid
      items = klass.of_projects(project_id).where(iid: iid)

      if items.size > 1
        puts "Remove #{klass.name} duplicates for iid: #{iid} and project_id: #{project_id}"
        items.shift
        items.each do |item|
          item.destroy
          puts '.'
        end
      end
    end
  end
end