Temporary Table class for creating a join table

temporary_table.rb

class TemporaryTable
  attr_reader :name_prefix, :attributes

  def initialize(name_prefix, attributes)
    @name_prefix = name_prefix
    @attributes = attributes
    create_temp_table!
  end

  def table_name
    @table_name ||= "#{name_prefix}_#{rand(1..9999)}"
  end

  def table
    @table ||= begin
      table_name = self.table_name
      
      Class.new(ActiveRecord::Base) do
        self.table_name = table_name
      end
    end
  end

  # Bulk insert relies on a multi-dimensional array that has the values in 
  # the order of the attributes passed in.
  def bulk_insert(objects)
    values = objects.each_with_object([]) do |object, collection|
      if object.is_a? Array
        line = object.map {|v| "'#{ActiveRecord::Base::sanitize(v)}'" }.join(", ")
      else
        line = "'#{ActiveRecord::Base::sanitize(object)}'"
      end

      collection << "(#{line})"
    end

    columns = attributes.keys.join(",")
    conn.execute("INSERT INTO #{table_name} (#{columns}) VALUES #{values.join(", ")}")
  end

  def index(column)
    conn.execute("ALTER TABLE #{table_name} ADD INDEX `#{column}` (`#{column}`)")
  end

  def drop!
    return unless exists?
    conn.execute("DROP TEMPORARY TABLE IF EXISTS #{table_name}")
    @exists = false
  end

  def exists?
    !!@exists
  end

  private

  def create_temp_table!
    return if exists?

    schema = attributes.keys.each_with_object([]) do |key, columns|
      columns << cast_attribute(key)
    end

    sql = "CREATE TEMPORARY TABLE #{table_name} ("
    sql << schema.join(",\n")
    sql << ")"

    conn.execute(sql)

    @exists = true
  end

  def cast_attribute(key)
    case attributes[key]
    when "integer"
      "#{key} INTEGER(11) NOT NULL"
    else
      "#{key} VARCHAR(255)"
    end
  end

  def conn
    ActiveRecord::Base.connection
  end
end