I found myself today trying to do this, and failing:
#!/usr/bin/env ruby
require 'rubygems'
require 'dm-core'
DataMapper.setup(:default, "sqlite3://#{Dir.pwd}/page.sqlite3")
class Page
include DataMapper::Resource
property :id, Serial # primary serial key
property :body, String # cannot be null
property :derived1, String
after :save, :after_save
def after_save
if attribute_get(:derived1).nil?
attribute_set(:derived1,body.to_s + ".db")
self.save
end
end
end
DataMapper.auto_migrate!
p = Page.new({ :body => "test123" })
p.save
p1 = Page.get(1)
puts p.inspect # derived1 => body + .db
puts p1.inspect # derived1 => nil
Initially, I was trying to make a field be a default of (item.id).to_s
+ "something", but this doesn't work with :default since attribute_get
isn't available to the class methods defining properties. So I came
up with something equivalent to this, and fought it for a while.
I'm working around this now just fine--it was just a naive thing for
the first round of specs--but why does self.save not work in
after_save here? If it's failing on purpose (which I can imagine,
given the risk of infinite recursion with poor programming), wouldn't
it be better to raise an exception than to silently, magically fail?
Perhaps at least not return true?
Thanks,
Ben
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