PostgreSQL Large Object Data Store for Dragonfly

gistfile1.rb

# This is a Dragonfly data store using PostgreSQL Large Objects. It appears to work fine,
# but I ended up using a different solution in my project. Anyway, here you go.
#
class PostgresDataStore
  def write(content, opts={})
    data_oid = store_lo(content.data)
    meta_oid = store_lo(Marshal.dump(content.meta))
    "#{data_oid}/#{meta_oid}"
  end

  def read(uid)
    data_oid, meta_oid = uid.split('/')
    data = fetch_lo(data_oid)
    meta = Marshal.load(fetch_lo(meta_oid))

    data && [data, meta]
  end

  def destroy(uid)
    data_oid, meta_oid = uid.split('/')
    remove_lo(data_oid)
    remove_lo(meta_oid)
  end

private

  def store_lo(data)
    ActiveRecord::Base.transaction do
      identifier = connection.lo_creat
      lo = connection.lo_open(identifier, ::PG::INV_WRITE)
      connection.lo_truncate(lo, 0)
      connection.lo_write(lo, data)
      connection.lo_close(lo)
      return identifier
    end
  end

  def fetch_lo(identifier)
    ActiveRecord::Base.transaction do
      lo = connection.lo_open(identifier.to_i)
      size = connection.lo_lseek(lo, 0, 2)
      connection.lo_lseek(lo, 0, 0)
      content = connection.lo_read(lo, size)
      connection.lo_close(lo)
      return content
    end
  end

  def remove_lo(identifier)
    ActiveRecord::Base.transaction do
      connection.lo_unlink(identifier.to_i)
    end
  end

  def connection
    ActiveRecord::Base.connection.raw_connection
  end
end

See this comment for some background information regarding its usability.