Using state attributes to maintain old records in Rails - ruby-on-rails

Question

I want to keep old records that would be normally destroyed. For example, an user joins a project, and is kicked from it later on. I want to keep the user_project record with something that flags the record as inactive. For this I use a state attribute in each model to define the current state of each record.
Almost all my "queries" want just the "active" records, the records with state == 1, and I want to use the ActiveRecord helpers (find_by etc). I don't want to add to all the "find_by's" I use a "_and_state" to find only the records that are active.
This is what I have now:
u = UserProject.find_by_user_id_and_project_id id1, id2
This is what I will have for every query like this for all models:
u = UserProject.find_by_user_id_and_project_id_and_state id1, id2, 1
What is the most cleaner way to implement this (the state maintenance and the cleaner query code)?

Answer 1

create a scope in your model UserProject:
class UserProject < ActiveRecord::Base
scope :active, where(:state => 1)
end
and "filter" your queries:
u = UserProject.active.find_by_user_id_and_project_id id1, id2
if you "almost allways" query the active UserProjects only, you can define this scope as default_scope and use unscoped if you want to query all records:
class UserProject < ActiveRecord::Base
default_scope where(:state => 1)
end
u = UserProject.find_by_user_id_and_project_id id1, id2 # only active UserProjects
u = UserProject.unscoped.find_by_user_id_and_project_id id1, id2 # all states

Answer 2

Here's a range of soft deletion gems you may want to choose from, which offer a nice abstraction that's already been thought through and debugged:
rails3_acts_as_paranoid
acts_as_archive
paranoia
Although if this happens to be your first Rails app, I second Martin's advice of rolling your own implementation.

Answer 3

I tried to just add this to Martin's answer, but my edit has to be reviewed, so even though Martin's answer was great, we can improve on it a little with the idea of default scopes. A default scope is always applied to finders on the model you add them to unless you specifically turn off the default scope:
class UserProject < ActiveRecord::Base
default_scope where(:state => 1)
end
The example Martin gave then becomes:
u = UserProject.find_by_user_id_and_project_id id1, id2
In this case, even without specifying that you want state == 1, you will only get active records. If this is almost always what you want, using a default scope will ensure you don't accidentally leave off the '.active' somewhere in your code, potentially creating a hard-to-find bug.
If you specify your default scope like this:
default_scope :conditions => {:state => 1}
then newly created UserProjects will already have state set to 1 without you having to explicitly set it.
Here's more information on default scopes: http://apidock.com/rails/ActiveRecord/Base/default_scope/class
Here's how to turn them off temporarily when you need to find all records:
http://apidock.com/rails/ActiveRecord/Scoping/Default/ClassMethods/unscoped