Merging three Active Record arrays - ruby-on-rails

Question

I'm trying to merge three Active Record arrays in a Rails 5 app so that I have a nice collection of jobs, forum threads and blogs on my home page.
I have the following code:
application_controller.rb
def home
#blogs = Blog.limit(6)
#jobs = Job.where(approved: true).limit(6)
#forum_threads = ForumThread.includes(:forum_posts).limit(6)
#everything = #blogs + #jobs + #forum_threads
end
home.html.erb
<% #everything.sort_by(&:created_at).reverse.each do |item| %>
<% if item.is_a?(Job) %>
<%= render partial: "application/partials/home_job", locals: {item: item} %>
<% elsif item.is_a?(ForumThread) %>
<%= render partial: "application/partials/home_forum", locals: {item: item} %>
<% elsif item.is_a?(Blog) %>
<%= render partial: "application/partials/home_blog", locals: {item: item} %>
<% end %>
<% end %>
The problem I'm having is that this code doesn't display the records in date order by created_by, instead I have a rather random collection of jobs, forum threads and blogs starting at a seemingly random date.
If I add, say, a new job, it doesn't appear in the collection displayed on /home page. However, if I delete all records from the db and start adding new records then the code works fine and displays the posts in the correct order with the behaviour I expect.
I can't push this code live to Heroku because I can't delete all the records that already exist in production. It's almost like there's some kind of cache that needs clearing out. Does anyone know what's going on?

Answer 1

#blogs = Blog.order(created_at: :desc).limit(6)
etc.

Answer 2

Problem 1: Getting the right records from the database
Option A: If you will always be sorting each model by the created_at value (a common desire), add a default_scope to each model (Rails 4+ version below). Your limit calls in the controller will automatically take advantage of the default scope.
app/models/blog.rb
class Blog < ActiveRecord::Base
default_scope { order created_at: :desc }
...
end
Option B: If you only do this in certain circumstances, but you do it for several models, I like to extract that into a Timestamped module (below). You will need to use the most_recent method in your controller when extracting records from the database to ensure you're getting the most recent ones.
app/models/concerns/timestamped.rb
module Timestamped
extend ActiveSupport::Concern
included do
scope :most_recent, -> { order created_at: :desc }
scope :least_recent, -> { order created_at: :asc }
scope :most_fresh, -> { order updated_at: :desc }
scope :least_fresh, -> { order updated_at: :asc }
end
end
class Blog < ActiveRecord::Base
include Timestamped
...
end
Problem 2: Sorting the array
Even with a simple case like this, I'd recommend adding an array extension that matches the most_recent method that timestamped.rb defines for ActiveRecord::Relations.
lib/array_extensions.rb
class Array
def most_recent
sort { |a, b| b.created_at <=> a.created_at }
end
end
and then require the extension with an initializer:
config/initializers/extensions.rb
require 'array_extensions'
Problem 3: Keeping the controller clean.
Generally each controller action should only set up one instance variable, and in this case it looks like you are not even using the #blogs, #jobs, and #forum_threads variables in the views. Vivek's answer solves this, although I'd do the flattening and sorting logic in the controller:
def home
#posts = Blog.most_recent.limit(6) + Job.approved.most_recent.limit(6) + ForumThread.most_recent.includes(:forum_posts).limit(6)
#posts = #posts.most_recent
end
Problem 4: Minimize if/then logic in your view
Instead of this:
<% #everything.sort_by(&:created_at).reverse.each do |item| %>
<% if item.is_a?(Job) %>
<%= render partial: "application/partials/home_job", locals: {item: item} %>
<% elsif item.is_a?(ForumThread) %>
<%= render partial: "application/partials/home_forum", locals: {item: item} %>
<% elsif item.is_a?(Blog) %>
<%= render partial: "application/partials/home_blog", locals: {item: item} %>
<% end %>
<% end %>
Do this:
<% #everything.sort_by(&:created_at).reverse.each do |item| %>
<%= render "application/partials/home_#{item.class.name.underscore}", item: item %>
<% end %>
And make sure your partials are named appropriately

Answer 3

You can do like this:
def home
#collections=[]
#collections << Blog.limit(6)
#collections << Job.where(approved: true).limit(6)
#collections << ForumThread.includes(:forum_posts).limit(6)
end
<% #collections.flatten.sort_by(&:created_at).reverse.each do |item| %>
....iteration here ....
<% end %>

Answer 4

if i understood your question correctly, you want to sort the array after you merged it by date. I would do it like that:
#everything = #everything.sort {|x| x.created_at }
Hope that helps.