Manipulating ActiveRecords using only a few attributes with Ruby on Rails

Question

Hi,

For caching matters, I'm caching an array of the attributes of the objects I need:

friends = [{:id => 4, :name => "Kevin"}, {:id => 12, :name => "Martin"}, …]

Is it possible to have a list of Users using this array, so that I can use Ruby methods? For instance, I usually get a list of non-friends with this:

non_friends = User.all - current_user.friends

Here, current_user.friends would be replaced by the cached array, only with the cached attributes:

friends = [
    #<User id: 4, name: "Kevin", created_at: nil, updated_at: nil, email: nil>,
    #<User id: 12, name: "Martin", created_at: nil, updated_at: nil, email: nil>,
    …
]

Is it possible? Is it a good approach to caching? (a big list of ActiveRecords doesn't fit into a 1MB Memcache chunk.)

Thank you,

Kevin

edit: The idea behind this is to use a sorted/processed list of 2000 ActiveRecords around which my app heavily uses, but since it doesn't fit into a Memcache chunk, I'm trying to cache the interesting attributes only as an array. Now, how can I use this array like it was an ActiveRecord array?

Answer 1

Well, you can just cache the User IDs and then exclude these IDs in your finder conditions. In your example, assuming you have a friends array of hashes containing ids and names:

friend_ids = friends.map{ |f| f[:id] }
if friend_ids.empty?
  non_friends = User.all
else
  non_friends = User.all(:conditions => ['id NOT IN (?)', current_user.friend_ids])
end