How do I enter a record for every user where condition is true in Rails - ruby-on-rails

Question

So I have app that has political candidates.
When a new political candidate is entered, I want to enter a notification into the notifications table for every user that's state is equal to the state of the new candidate being entered.
Ultimately, I want to enter in records to the notification table for every single user where that condition is met.
I know I'm way off, but here's where I'm at now. I'm trying to loop through each user and then enter this record when that condition is true.
def create
#candidate = Candidate.new(candidate_params)
if #candidate.save
User.each do |u|
if Candidate.state == User.state
#notification = Notification.new(:message => 'Message', :user_id => U.id)
#notification.save
else
end
end
else
render('new')
end
end
The candidate is created with this code, but the notifications aren't working. Basically I have two users where their state equals "Arizona" and I would expect if I create a new candidate where the state is "Arizona" that I should get two record into notifications, one with each user ID.

Answer 1

I think you got a bit mixed up between classes and instances. Here's the relevant bit:
#candidate = Candidate.new(candidate_params)
...
User.each do |u|
if Candidate.state == User.state
...
end
end
In your code Candidate is a class, and #candidate holds the recently created instance of a Candidate. Likewise, User is a class and u holds a User instance (on each loop iteration). Your comparison should actually use the instances rather than the classes:
if #candidate.state == u.state
Having sorted that, it's worth noting that your code has a couple of other errors -- User.each won't work. You need to specify a selector to get a list of User objects to loop through. One way would be to call User.all.each (which looking at your code is probably what you were trying). That pulls all User objects. But, since users can be from anywhere, if you do that you will cycle through a lot of users you don't need to.
Since all you need is users whose state matches the new candidate, you can use the where() method to pre-filter the list you are looping through. That way you don't need the if at all.
#candidate = Candidate.new(candidate_params)
...
User.where(state: #candidate.state).each do |u|
#notification = Notification.new(message: 'Message', user: u)
#notification.save
end
The other problem in your code is in the line to create a notification. You use U.id but the loop variable is lower case u. As an added tip, you don't need to set the object ID specifically. If you just pass the User object (as in the code above), Rails is smart enough to figure out the rest.

Answer 2

For performance don't iterate all users, you can search users that match the candidate's state then create notification for each user.
def create
#candidate = Candidate.new(candidate_params)
if #candidate.save
users = User.where(state: #condidate.state)
users.each { |user| #notification = Notification.create(:message => 'Message', :user_id =user.id } if users
else
render 'new'
end
end