Steps

Step 1: Teach the Topic model about Votes

Edit app/models/topic.rb so that it looks like this:

class Topic < ApplicationRecord
  has_many :votes, dependent: :destroy
end

Step 2: Teach the Vote model about Topics

Look into app/models/vote.rb and confirm that it looks like this:

class Vote < ApplicationRecord
  belongs_to :topic
end

Step 3: Play around with Topics and Votes in the Rails console

First, make sure you've made at least one topic on the site.

Next, open a Rails console in the shell window:

rails console

Approximate expected result:

~/RandomWittyName$ rails console
Loading development environment (Rails 7.0.1)
irb(main):001:0>

The greyed-out text may differ and is not important.

Are you typing into the shell or are you typing into the rails console? This makes a big difference. You can always tell the two apart by the prompt

At the console, try the following things

See how many topics exist:

Topic.count

Approximate expected result:

irb(main):001:0> Topic.count
  Topic Count (0.2ms)  SELECT COUNT(*) FROM "topics"
=> 2

The greyed-out text may differ and is not important.

• On the first line you see
  • the irb-prompt ending in with a greater-than sign, and after that
  • the code you typed in
• on the second line, you can see (from right to left)
  • the SQL Query that was sent to the database SELECT COUNT(*) FROM "topics"
  • that it took 0.2ms to run that Query
  • that it was run to compute the Topic count
• on the third line you see
  • a "fat arrow" =>
  • and after that the result: there is are two topics in this database

Most of the time you are only intrested in the last line with the result.

Save the first topic into a variable:

my_topic = Topic.first

my_topic here could have been any variable name, but we'll stick with my_topic for consistency.

Change the title of that topic to something else:

my_topic.update(title: 'Edited in the console')

Reload the page in the browser and you will see the change:

Add a vote to that topic:

my_topic.votes.create

See how many votes that topic has:

my_topic.votes.count

Remove a vote from that topic:

my_topic.votes.first.destroy

Note that the things you can do to Model classes (like Topic and Vote), differ from the things you can do to Model instances (like my_topic, here). my_topic.votes is an association, and here behaves mostly like a model class.

Model class / association methods

• Topic.first
• Topic.last
• Topic.all
• Topic.count
• Topic.find_by_id(5)
• Topic.destroy_all
• my_topic.votes.count
• my_topic.votes.create
• my_topic.votes.destroy_all

Model instance methods

• my_topic.title
• my_topic.title = 'New title'
• my_topic.update_attributes(title: 'New title')
• my_topic.save
• my_topic.save!
• my_topic.destroy
• my_topic.votes.first.destroy

An exhaustive list of things you can do to models and associations can be found in the Active Record Query Interface RailsGuide.