join

# File activerecord/lib/arel/select_manager.rb, line 104
    def join(relation, klass = Nodes::InnerJoin)
      return self unless relation

      case relation
      when String, Nodes::SqlLiteral
        raise EmptyJoinError if relation.empty?
        klass = Nodes::StringJoin
      end

      @ctx.source.right << create_join(relation, nil, klass)
      self
    end