class ActiveRecord::Relation::Merger

def merge_joins
  return if values[:joins].blank?
  if other.klass == relation.klass
    relation.joins!(*values[:joins])
  else
    joins_dependency, rest = values[:joins].partition do |join|
      case join
      when Hash, Symbol, Array
        true
      else
        false
      end
    end
    join_dependency = ActiveRecord::Associations::JoinDependency.new(other.klass,
                                                                     joins_dependency,
                                                                     [])
    relation.joins! rest
    @relation = relation.joins join_dependency
  end
end