Example of has_many with dynamodb

fetch_all_songs_of_a_movie.rb

# fetch a movie
m = Movie.first
# fetch songs
songs = m.get_songs

movie.rb

class Movie
  include ActiveModel::Model, ActiveModel::Serialization

  attr_accessor :name
  attr_accessor :year
  attr_accessor :released
  attr_accessor :created_at
  attr_accessor :actor
  attr_accessor :actress
  attr_accessor :songs_ids
  attr_accessor :updated_at

  def self.migrate_table
    migration = Aws::Record::TableMigration.new(self)
    migration.create!(
        provisioned_throughput: {
            read_capacity_units: 1,
            write_capacity_units: 1
        },
        global_secondary_index_throughput: {
            actor_actress_index: {
                read_capacity_units: 1,
                write_capacity_units: 1
            },
        }
    )
    migration.wait_until_available
  end

  def self.first
    movie = $ddb.scan({
                   table_name: "movies",
                   limit: 1
              }).items.first
    Movie.new(movie)
  end
  
  def get_songs
    song_names = self.songs_ids.to_a
    expression_attrs = []
    song_names.each do |name|
      expression_attrs << { "name" => name }
    end

    batch_get_query = {
        request_items: {
            "songs" => {
                keys: expression_attrs
            }
        }
    }

    songs_array = $ddb.batch_get_item(batch_get_query).responses["songs"]
    songs_array.map { |song| Song.new(song) }
  end
end

Song.rb

class Song
  include ActiveModel::Model, ActiveModel::Serialization
  
  attr_accessor :name
  attr_accessor :movie_ids
  attr_accessor :created_at
  attr_accessor :updated_at
  
  def self.migrate_table
    migration = Aws::Record::TableMigration.new(self)
    migration.create!(
        provisioned_throughput: {
            read_capacity_units: 1,
            write_capacity_units: 1
        },
        global_secondary_index_throughput: {
            actor_actress_index: {
                read_capacity_units: 1,
                write_capacity_units: 1
            },
        }
    )
    migration.wait_until_available
  end
  
end