I've recently started an internship. My employer uses ruby on rails, and I frequently encounter new syntax that I need to look up to understand. I've googled around for a good explanation of named_scope, but what I've found so far is mostly blog posts giving high praise for it, rather a straight definition or introduction.
What exactly is named_scope (now simply called scope) in ruby on rails?
A scope is a subset of a collection. Sounds complicated? It isn't. Imagine this:
You have Users. Now, some of those Users are subscribed to your newsletter. You marked those who receive a newsletter by adding a field to the Users Database (user.subscribed_to_newsletter = true). Naturally, you sometimes want to get those Users who are subscribed to your newsletter.
You could, of course, always do this:
User.where(subscribed_to_newsletter: true).each do #something
Instead of always writing this you could, however, do something like this.
#File: users.rb
class User < ActiveRecord::Base
scope :newsletter, where(subscribed_to_newsletter: true)
#yada yada
end
If you're using Rails 4 or newer, do this instead:
#File: users.rb
class User < ActiveRecord::Base
scope :newsletter, -> { where(subscribed_to_newsletter: true) }
#yada yada
end
This allows you to access your subscribers by simply doing this:
User.newsletter.each do #something
This is a very simple example but in general scopes can be very powerful tools to easy your work.
Check out this link: API Description