basic support for PostgreSQL sequences in ActiveRecord migrations - place in an initializer

pg_sequence.rb

module PgSequence
  module PostgreSQLAdapter
    def create_sequence(name)
      execute "CREATE SEQUENCE #{name}"
    end

    def drop_sequence(name)
      execute "DROP SEQUENCE #{name}"
    end
  end
end

ActiveRecord::ConnectionAdapters::PostgreSQLAdapter.class_eval do
  include PgSequence::PostgreSQLAdapter
end

ActiveRecord::ConnectionAdapters.module_eval do
  include PgSequence::PostgreSQLAdapter
end

module PgSequence
  module SchemaDumper
    extend ActiveSupport::Concern

    included do
      alias_method_chain :tables, :sequences
    end

    def tables_with_sequences(stream)
      tables_without_sequences(stream)
      sequences(stream)
    end

    private
    def sequences(stream)
      sequence_names = @connection.select_all("SELECT c.relname FROM pg_class c WHERE c.relkind = 'S' order by c.relname asc")
        .map { |row| row['relname'] }

      # ignore any sequences that end in 'id_seq', as these are generated by rails for primary keys
      # and are added implicitly by the migrator
      statements = sequence_names.reject {|seq| seq.end_with? 'id_seq'}.map do |seq|
        "  create_sequence(#{seq.inspect})"
      end
      
      stream.puts statements.sort.join("\n")
      stream.puts
    end

  end
end

ActiveRecord::SchemaDumper.class_eval do
  include PgSequence::SchemaDumper
end