simple mapper

file.rb

require_relative 'links'
require_relative 'tags'

module Foil
  class File
    attr_accessor :id,
      :category_id, :license_id, :visibility_id,
      :description, :name,
      :annotations, :authors, :editors, :links, :publishers, :tags

    def initialize(attributes)
      @id             = attributes['id']

      @category_id    = attributes['category_id']
      @license_id     = attributes['license_id']
      @visibility_id  = attributes['visibility_id']

      @description    = attributes['description']
      @name           = attributes['name']

      @annotations    = Array attributes['annotations']
      @authors        = Array attributes['authors']
      @editors        = Array attributes['editors']
      @links          = Array attributes['links']
      @publishers     = Array attributes['publishers']
      @tags           = Array attributes['tags']
    end

    def links
      @links ||= Links.for_file(id)
    end

    def tags
      @tags ||= Tags.for_file(id)
    end
  end
end

files.rb

require_relative 'db'
require_relative 'file'

module Foil
  class Files
    include Enumerable

    def initialize(db: Foil::DB.new, model: Foil::File)
      @db    = db
      @model = model
      prepare
    end

    def [](id)
      @db.exec_prepared('find_file', [id])
        .map {|r| @model.new(r) }
        .first
    end

    def for_folder(id)
      @db.exec_prepared('find_files_for_folder', [id])
        .map {|r| @model.new(r) }
    end

    def each(&block)
      @db.exec('SELECT * FROM files')
        .lazy
        .map {|attributes| @model.new(attributes)}
        .each(&block)
    end

    def <<(i)
      @db.exec_prepared('insert_file', values(i))
        .map {|r| @model.new(r) }
        .first
    end

    def []=(id, i)
      @db.exec_prepared('update_file', [id] + values(i))
        .map {|r| @model.new(r) }
        .first
    end

    def -(f)
      @db.exec_prepared('delete_file', [i.id])
      instance
    end

    private

    def prepare
      @db.prepare('find_files_for_folder',
        'SELECT f.id, f.name FROM files f JOIN filings fs ON (fs.file_id = f.id AND fs.folder_id = $1)')
      @db.prepare('find_file',
        'SELECT * FROM files WHERE id = $1')
      @db.prepare('insert_file',
        'INSERT INTO files (category_id, license_id, visibility_id, description, name) VALUES ($1, $2, $3, $4, $5) returning *')
      @db.prepare('update_file',
        'UPDATE files SET category_id=$2, license_id=$3, visibility_id=$4, description=$5, name=$6 WHERE id=$1 returning *')
      @db.prepare('delete_file',
        'DELETE FROM files WHERE id=$1')
    end

    def values(i)
      [i.category_id, i.license_id, i.visibility_id,
        i.description, i.name]
    end
  end
end