[PATCH] define_schema for Active Resource

Ok, so Josh suggested I make a ticket for this for better tracking.

I've built some baseline functionality for defining a schema for an Active Resource.

Code available as a patch here: http://pastie.org/743842
and a more-readable combined diff here: http://pastie.org/743843

What you can now do is this:

class FlickrPhoto << ActiveResource::Base

define_schema do |s|
  s.string :photo, :title
  s.integer :width, :height
  s.float :some_other_attribute
  s.attribute 'and_another', 'string'
end

validates_presence_of :photo
validates_numericality_of :width, :height

end

# this works my_photo = FlickrPhoto.new(:photo => 'photo_stream_here', :title => 'eben', :tags => ['cat']) my_photo.valid? # => true my_photo.save # => true my_photo.photo # 'photo_stream_here'

# and now, so does this: new_photo = FlickrPhoto.new() new_photo.respond_to? :photo # => true new_photo.photo # => nil new_photo.valid? # => false

new_photo.known_attributes # => ['photo', 'title', 'height', 'width', 'some_other_attribute', 'and_another']

# and if you fetch and existing one: a_photo = FlickrPhoto.find(1) # abcdef123<instance_attribute>456</instance_attribute> a_photo.photo # => 'abcdef' a_photo.width # => '123' # note: still a string a_photo.instance_attribute # => '456' # note: also a string

a_photo.known_attributes # => ['photo', 'title', 'height', 'width', 'some_other_attribute', 'and_another', 'instance_attribute']

new_photo.respond_to? 'instance_attribute' # => false (because it's not a known_attribute)

More details on what/how in the rdoc for define_schema :)

To summarise:

1) You can define a schema using 'define_schema' and passing a block, or passing a hash to 'schema='

2) this populates a set of 'known_attributes' that are added to the list of attributes currently on an instance (if there's no schema, this means that the known_attributes equals the existing attributes on the instance - as it always has done).

3) known attributes will return 'true' to a 'respond_to?' and will not cause a 'NoMethodError' if invoked

4) it will also store the 'attribute type' against each attribute - currently this does nothing... but my next step is to add a typecast based on this, along with "attributes_before_typecast" ala Active Record. This will be extremely useful for integer values as I've found my own code peppered with "to_i" checks for attributes that I already know are meant to be integers :P

5) an extension will also allow us to pass in options. The only sensible one that I can see so far is ":default => 'blah') which will, of course, set up known attributes with their given defaults - unless otherwise specified.

This functionality follows from the original discussion-thread here:
http://groups.google.com/group/rubyonrails-core/browse_thread/threa...
and then here:
http://groups.google.com/group/rubyonrails-core/browse_thread/threa...

Future extensions:

1) using 'instance_eval' to get rid of the 'do |s|' syntax
2) Making the attribute-type actually do something useful (in this case: automatically typecast returned values as described above)
3) adding the 'default' option that will auto-populate the so-specified attributes on initialize