Title pretty much explains it. I'd like to set a variable the stores a single Model object inside of application.rb since it will be used on every single page. I've tried both class and instance variables, but to no avail. The only thing that worked so far was using a global ($) variable.
So why not use that, then? Whatever works...
Also, you might brush up on MVC and beginner's Ruby as far as "setting variables in models" go: http://wiki.rubyonrails.org/rails/pages/UnderstandingRailsMVC
I don't generally follow the "whatever works..." approach because there is usually a best practice. That said, I want to avoid the global variable because having $tidbit = Tidbit.random declared in my application.rb broke my migrations. Running migrations from version 0 when the Tidbits database doesn't exist caused the db:migrate to fail because the line of code was still being executed and the Model was attempting to access a table that didn't exist.
I'll keep reading, but I'm sure there is a logical way of accomplishing this that I'm just not yet seeing. Thanks.
Hi Eric,
Title pretty much explains it. I'd like to set a variable the stores a single Model object inside of application.rb since it will be used on every single page. I've tried both class and instance variables, but to no avail. The only thing that worked so far was using a global ($) variable.
It sounds like, maybe you're setting it once in application.rb rather than once per request/response cycle? Instance variables (and IIRC class variables too) have a one-cycle lifetime. That would explain why a global 'works'.
The 'typical' approach to setting an instance variable that's needed for every render would be to add a before_filter in all your controllers that invokes the application.rb method.
HTH, Bill
To initialize some db-read var (tidbit in your example) that would survive and be callable for each subsequent app request, you'll want to do so via lazy-initialization using a before_filter (mentioned by bill) in application.rb.
How you store such lazy-init vars between requests depends on the scope/use of such vars by users/requests of the app:
If the var that you're setting is specific to some user alone, and should not be shared by all users' requests, then you could store that var in the user's session:
# in ./app/controller/application.rb ... before_filter :do_lazy_init
... private
def do_lazy_init session[:tidbit] = Tidbit.random if not session[:tidbit] @tidbit = session[:tidbit] end
which all of your app controller meths and view templates could then use via @tidbit.
Note that such session vars can survive app restarts. So if you really want the var to be set at app start/restart, and/or you change the structure/content of tidbit in the db, you'll want to clear such session data first before re-starting your app.
If var that you're setting really is global in scope, intended to be shared by all users' requests and is read-only, then you could store it in a global var:
# in ./app/controller/application.rb ... before_filter :do_lazy_init
... private
def do_lazy_init $global_tidbit = Tidbit.random if not $global_tidbit @tidbit = $global_tidbit end
Beware of issues surrounding use of global vars tho, and definitely don't use mutable global vars, due to potential data incongruity issues, especially when running production environment (assuming more than one process-/thread-instance of your app in prod env).
If you're interested in Matz's opinion on use of global vars, per quote in Ruby Pocket Ref (Google Books? id=KZU_HUYJ5yMC&pg=PA13&dq=ruby+matz+global+variables): "They're ugly, so don't use them."
Jeff
For actual read-only data that is an instance of a model class, I'd set up a class method instead. So for a default location, in Location.rb,
def self.default_location @@default_location ||= Location.find_by_name("San Francisco") end
This fixes your migration problem, doesn't reload it with every page, and also works with testing.
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If var that you're setting really is global in scope, intended to be shared by all users' requests and is read-only, then you could store it in a global var:
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hi, Ruby pocket reference looks useful, think I'll order a copy. Regarding the class method, just wondering when/how this method should get called.
Tonypm
Thanks, this sounds like what I need.