Thanks for this Florian. I really appreciate the help. I have to admit
though being a rails and ruby newbie, I'm a bit confused by it (ok
maybe a lot confused.) (I'm a seasoned Java/JEE guy though so I'm not
having too much trouble catching on too ruby and rails.)
I've never seen a non ActionRecord object work as being persisted and
retrieved. In the case below AutomobileItem is that object that could
act as being retrieved from a db or a webservice (and as a collection
like you have shown.) I think some of the info that is left out in the
comment block in def self.from_database(automobile) I might need to
see. Say I wanted to get a single AutomobileItem out of the db by the
automoblileID how is it done? I take it's something like setting an
AutomobileItem with the id and then passing it to the
from_database(automobile) method? I'm just clueless on how that would
work? (I probably need to find a document or something online
explaining it? I have the Agile Web Development with Rails pdf but I
don't think that covers this?)
Also what if just wanted all automobiles.. since I don't have a
AutomobileItem.find(:all), what would I call?
Sorry for these probably ignorant questions, it's just a bit difficult
for me since almost all the examples I'm finding deal with pure
ActiveRecord objects.
(Not that it matters but in real life this isn't working with
Automobiles, but rss feeds. I'm currently using Hobo migrations and my
models look like:
class RssFeed < ActiveRecord::Base
fields do
title :string
body :text
authors :string
entry_url :string
timestamps
end
belongs_to :rss_feed_source
end
class RssFeedSource < ActiveRecord::Base
fields do
name :string
url :string
timestamps
end
has_many :rss_feeds
#used for non persistent feeds
attr_accessor :feeds
#tried declaring array in def intitialize but must have done it wrong
def add_feed(feed)
@feeds = [] if @feeds == nil
@feeds << feed
end
end
//see now annoying because I had to create this non persistent object
that mimics the RssFeed class!
class RssFeedNonpersistent
attr_accessor :title, :body, :authors, :entry_url
end
On Fri, Jan 2, 2009 at 11:39 PM, Florian Aßmann
<[email protected]> wrote:
>
> Hi Rick, hope I got it right:
>
> class AutomobileManufacturer < ActiveRecord::Base
> has_many :automobiles
>
> def favorite_automobiles
> AutomobileCollection.from_association_collection automobiles
> end
> def all_automobiles
> favorite_automobiles | remote_automobiles
> end
> def remote_automobiles
> AutomobileCollection.from_webservice
> end
>
> end
>
> class AutomobileCollection
>
> def self.from_association_collection(collection)
> collection = collection.map { |a| AutomobileItem.from_database a }
> new collection
> end
> def self.from_webservice
> # load collection... or take it as argument
> collection = collection.map { |a| AutomobileItem.from_webservice
> a }
> new collection
> end
>
> # generate a hash to simplify intersect
> def initialize(collection)
> @collection_hash = collection.inject({}) { |hash, item|
> hash.merge item.identifier => item
> }
> @collection = collection
> end
>
> # this could possibly be done with ruby stdlib 'Delegate'
> def each(&block)
> @collection.each(&block)
> end
>
> # intersect with another automobile collections
> def |(other)
> new_keys = other.automobiles_hash.keys - @collection_hash.keys
> new_collection = @collection +
> other.automobiles_hash.values_at(*new_keys)
>
> self.class.new new_collection
> end
>
> class AutomobileItem
>
> # two seperate methods because I think the interface for
> # webservice automobile and database automobile wont match.
>
> def self.from_webservice(automobile)
> instance = new automobile.manufacturer # ...
> instance
> end
> def self.from_database(automobile)
> instance = new automobile.manufacturer # ...
> def instance.favor
> # nop ...
> end
> instance
> end
>
> def initialize(manufacturer, *further_attributes)
> @attributes_hash = {
> # ...
> }
> end
> # generate an unique but compareable identifier
> def identifier
> "#{ manufacturer } ..."
> end
> # save the record, or maybe not when boxed automobile was loaded
> from db...
> def favor
> Automobile.create @attributes_hash
> # nop
> def self.favor; end
> end
> end
>
> end
>
> To make a subclass of ActiveRecord::Base to something not subclassing
> it requires some voodoo magic. If you really interested in this kind
> of stuff you should gte yourself involved with the rubiunius project. ;)
> Otherwise box them in something that would provide the same interface
> for SOAPed objects as for ORMed objects.
>
> This code is fully untested, but I hope you get the idea.
>
> Regards
> Florian
>
> Am 02.01.2009 um 20:46 schrieb Rick:
>
>>
>> I understand I can just define a class without extending
>> ActiveReord::Base, but what if I want to use the model object
>> sometimes without having the data persist. For example...
>>
>> Let's say I have an "AutoManufacturer" object it might have
>> name=Mercedes,etc. But AutoManufacturer could contain a collection of
>> "Automobile" objects, (class=CLS, model="CLS350, numberOfDoors=4").
>> Maybe your db isn't the one storing ALL the Automobile objects, you
>> might only want to store 'favorite automobiles' but you still want to
>> collect all the Automobile information (class, model, etc) when you
>> record a favorite.
>>
>> So now what if I go to my DB and get my "AutoManufacturer" objects and
>> for each AutoManufacturer I query some webservice to return a list of
>> Automobiles and I want to then display on a page the AutoManufacturers
>> and a collection of the Automobile objects I returned from my
>> webservice call. If I have "Automobile" defined as an ActiveRecord
>> type when I do something like....
>>
>> automobiles = getCarsFromWebservice()
>> automobiles.each do |a|
>> car = Automobile.new();
>> car.class= a.class
>> car.type= a.type
>> autoManufacturer.autos << car
>> end
>>
>> every new car created above and added to the autoManufacturer actually
>> creates a new car in the db, In this case all I want is fully
>> populated list of autos in each autoManufacturer object for use to
>> display on the front end, but I don't really want the automobile added
>> to the db at this time. (Maybe after they select some, I'll then query
>> a webservice and populate a real Automobile that I do want to persist
>> in my db.)
>>
>> Currently I'm having to do something really lame. I'm creating
>> basically identical objects - one a model object and one a simple
>> pojo. It doesn't seem very dry to do it this way though. What's a
>> better approach?
>>
>> --
>> Rick
>>
>> >
>
>
> >
>
--
Rick
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