Show unread posts in Rails - ruby-on-rails

Question

Disclaimer: I'm a complete Rails n00b.
I need to present my forum users with a list of posts, where some might be 'unread'. By unread I mean that the post has a newer :updated_at timestamp than the user's last view timestamp of that post. I can't figure out the best approach for this - unread posts would obviously be unique to every user.
I tried using the 'Unread' gem but the documentation is above my comprehension, I can't get it to work (and I'm not even sure it does what I want it to do).
What's the leanest most Rails-y way to do this?
I'm on Rails 4.1.6
I currently have a user model and a post model:
class User
has_many :posts
end
class Post
belongs_to :user
end
See below for edits.
EDIT 1:
I tried following the example below of adding a Looks model, and I think I'm much closer to a solution (although not all the way there). Here's what I did:
1) rails g model Look post:references user:references + rake db:migrate. This obviously generated the model needed:
class Look
belongs_to :post
belongs_to :user
end
2) Edited my User and Post models:
class User
has_many :posts, through: :looks
has_many :looks
end
class Post
belongs_to :user
has_many :looks
has_many :users, through: :looks
end
3) Went into rails console:
user1 = User.first
post1 = Post.first
post2 = Post.last
look = Look.create(user: user1, post: post1)
look = Look.create(user: user1, post: post2)
4) I now tried to spit out the results:
seen = user1.posts
seen.map(&:title)
This works fine, it gives me the result of user1 having seen those two posts.
5) Then I tried just spitting out the IDs of the seen posts:
ids = Look.where(user: user1).pluck(:post_id)
This also works fine, I get a map of seen post ids => [2, 30]
6) I then managed to get around duplicate IDs by putting a .uniqat the end of User.first.posts.map(&:id).uniq
7) This is where I get stuck!:
Applying has_many :posts, through: :looks ruins the current relationship between a user and a post (the user_id is not included when creating a post). Here is my PostsController:
def create
#post = current_user.posts.build(post_params)
if #post.save
redirect_to #post
else
render 'new'
end
end
private
def post_params
params.require(:post).permit(:title, :content, :sticky, :ama_post, :post_url)
end
This is the last hurdle. I just need to make sure the user_id is included when creating a post.

Answer 1

Presuming you have a typical setup with many users and many posts, and you want to keep track whether any user has looked at any post, then you need to associate the users and posts by using a third model that joins a specific user to a specific post.
Start with the Rails guide: http://guides.rubyonrails.org/association_basics.html
Example models:
class User < ActiveRecord::Base
has_many :looks
has_many :posts, through: looks
end
class Post < ActiveRecord::Base
has_many :looks
has_many :users, through: looks
end
class Look < ActiveRecord::Base
belongs_to :user
belongs_to :post
end
Let's set up some sample data using the rails console:
alice = User.create(name: "Alice")
post1 = Post.create(name: "Post 1")
post2 = Post.create(name: "Post 2")
post3 = Post.create(name: "Post 3")
post4 = Post.create(name: "Post 4")
look = Look.create(user: alice, post: post1)
look = Look.create(user: alice, post: post2)
To find the posts that a user has seen:
seen = alice.posts
seen.map(&:name)
=> ["Post 1", "Post 2"]
To find the posts that a user has not seen:
ids = seen.map(&:id)
unseen = Post.where("id not in (?)", ids)
unseen.map(&:name)
=> ["Post 3", "Post 4"]
This is a simple way to get the records you want.
After you get this working, there are better ways to get the records by using query optimizations.
For example, you can retrieve much less data by getting just the id numbers. Here are a few ways.
# Basic: traverses two joins, then loads all columns
ids = Post.joins(:looks => :user).where("users.id = ?", alice.id).map(&:id)
# Faster: traverses two joins, then loads one column
ids = Post.joins(:looks => :user).where("users.id = ?", alice.id).pluck(:id)
# Fastest: no joins, and only loads one column
ids = Look.where(user: alice).pluck(:post_id)
Take a look at the unread gem for guidance and example code.

Answer 2

You'll probably need some sort of historical log. It can either log individual instances, or merely log the latest visit to the forum.
Here's a hypothetical scenario:
Your forum has only one forum group.
You have a User model for each user.
You have a Topic/Thread model that contains the individual topic, with a has_many relationship to:
The Post model which contains a specific post authored by a specific user (not relevant to answer but part of scenario)
Your forum has a Topic controller with the standard RESTful resource routes assigned.
What you want to do is separate/highlight/designate the unread topics from the read topics, right? Breaking that down, you need to:
Figure out when the user last visited the forum's index page.
Get a list of topics.
When rendering each topic in the list, determine whether the topic is more "recent" than the user's last visit. Regardless of whether it was created after the last visit, or had a post after the last visit.
Render it differently (or whatever) as per your requirements.
Turning that into a very simple implementation, you would:
Add a "last index visit" attribute to the User.
Load that value when visiting the index.
Render the topics accordingly.
Update the last index visit attribute on the current user (best implemented as an after_action)
Now this implementation assumes that you only want to keep track of it in one place and are OK with the limitations associated with that choice (reading an individual topic won't mark it as read).
If you wanted to, you could eliminate that limitation by creating a table that belongs to both the user and the topic, and then updating that table whenever the user 'reads' the topic (depending on whether you want them to view the topic or just see it in the index).
EDIT
To ultimately answer this question, you need to break it down into more details. "Identify unread topics" means you need to answer:
When do I consider a topic read? Is it when I view the individual posts since it is 'new'? Is it when I see the topic in a list after it is 'new'?
What do I consider a new/updated topic? Is it when it's first posted? what happens if someone posts a reply?
EDIT 2
Then I'd do the following:
Add a touch: true statement to the Post model's association to the Topic to ensure the updated_at attribute on the topic is modified whenever another post is made/edited.
Create a view helper method to determine whether the current user's last reading (if any) is later than the Topic's updated_at timestamp.
Create an after_action only on Posts#show that creates/updates the Reading for that user & topic.