join

# File activerecord/lib/arel/table.rb, line 42
    def join(relation, klass = Nodes::InnerJoin)
      return from unless relation

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

      from.join(relation, klass)
    end