#My model class looks like this:

class Cache
  include DataMapper::Resource

  property :id, Serial
  property :key, String
  property :data, Text, :lazy => false
  property :expires_at, DateTime
end

#I can't explain this output:

irb(main):002:0> c=Cache.first
=> #<Cache id=1 key="a" data="b" expires_at=nil>
irb(main):003:0> c.data="c"
=> "c"
irb(main):004:0> c.save
TypeError: can't convert String into Array
        from /usr/local/lib/ruby/gems/1.8/gems/dm-core-0.9.11/lib/dm-core/model.rb:394:in `zip'
        from /usr/local/lib/ruby/gems/1.8/gems/dm-core-0.9.11/lib/dm-core/model.rb:394:in `to_query'
        from /usr/local/lib/ruby/gems/1.8/gems/dm-core-0.9.11/lib/dm-core/resource.rb:543:in `to_query'
        from /usr/local/lib/ruby/gems/1.8/gems/dm-core-0.9.11/lib/dm-core/resource.rb:603:in `hookable__update_nan_before_advised'
        from /usr/local/lib/ruby/gems/1.8/gems/extlib-0.9.12/lib/extlib/hook.rb:299:in `update'
        from /usr/local/lib/ruby/gems/1.8/gems/extlib-0.9.12/lib/extlib/hook.rb:297:in `catch'
        from /usr/local/lib/ruby/gems/1.8/gems/extlib-0.9.12/lib/extlib/hook.rb:297:in `update'
        from /usr/local/lib/ruby/gems/1.8/gems/dm-core-0.9.11/lib/dm-core/resource.rb:295:in `hookable__save_nan_before_advised'
        from /usr/local/lib/ruby/gems/1.8/gems/extlib-0.9.12/lib/extlib/hook.rb:299:in `save'
        from /usr/local/lib/ruby/gems/1.8/gems/extlib-0.9.12/lib/extlib/hook.rb:297:in `catch'
        from /usr/local/lib/ruby/gems/1.8/gems/extlib-0.9.12/lib/extlib/hook.rb:297:in `save'
        from (irb):4
irb(main):005:0>