Forum: Ruby on Rails morphing an object among peer subclasses

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Brian M. (Guest)
on 2007-02-10 03:42
i'm trying to find the best way to swap an object among subclasses.  The
use case is changing among graph types (ex:

# the models are
BarGraph < Graph
LineGraph < Graph
ScatterGraph < Graph
class Graph < ActiveRecord::Base
  def change_type_to(target_type)
    graph.update_attributes :type =>

# so our code today looks like this
graph = BarGraph.create!

# change the graph from a bar graph to a line graph
new_graph = graph.change_type_to LineGraph
assert_equal LineGraph, new_graph.class # passes

#I would like to DRY it up a bit to look like this:
graph.change_type_to! LineGraph
assert_equal LineGraph, graph.class

I have also played with a separate GraphMorpher with a class method to
do this, but it felt too clunky.

It seems impossible to me.  But this is ruby.  Is there way?  Or a
better way to approach the whole use case?
Brian M. (Guest)
on 2007-02-10 03:44
sorry Graph#change_type_to

should be:

  def change_type_to(target_type)
    self.update_attributes :type =>
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