Question

How can I fetch records just like below with using Model and controler not view?

Pattern1. With helper

application_helper

def user_link(username)
    link_to User.find_by_username(username).user_profile.nickname, show_user_path(username)
end

view

<% @topics.order("updated_at DESC").limit(100).each do |topic| %>
    <%= user_link(topic.comment_threads.order("id").last.user.username) if topic.comment_threads.present? %>
<% end %>

Pattern2. Without helper. Just only view

<% @topics.order("updated_at DESC").limit(100).each do |topic| %>
    <%= link_to(topic.comment_threads.order("id").last.user.nickname, show_user_path(topic.comment_threads.order("id").last.user.username) ) if topic.comment_threads.present? %>
<% end %>

UPDATE

  <%  @community.topics.eager.recent.each do |topic| %>
    <%= user_link(topic.comment_threads.order("id").last.user.username) if topic.comment_threads.present? %>
  <% end %>

Answer 1

SQL code or SQL builders should never ever reach the view layer. This should be in your models. I wouldn’t even place queries like this in the controller.

I’d extract the topic SQL builder into a named scope. On top of that, to avoid n+1 queries, I’d create another named scope eager:

# topic.rb

scope :eager, includes(comment_threads: :user)
scope :recent, lambda { |n = 100| order("updated_at DESC").limit(n) }

Then I’d move the comment_threads SQL builder into your comment_threads model:

# comment_thread.rb

def self.last_user_nickname
  order("id").last.user.nickname
end

We can now tidy up your views:

<% @topics.eager.recent.each do |topic| %>
  <%= user_link(topic.comment_threads.last_user_nickname) if topic.comment_threads.present? %>
<% end %>

Allow me to sell Slim to you (erb alternative):

- @topics.eager.recent.each do |topic|
  = user_link(topic.comment_threads.last_user_nickname) if topic.comment_threads.present?

I might have even gone a step further and extracted the user_link into a UserDecorator. See https://github.com/drapergem/draper for details.

Summary

1. Extract SQL builder for topic into eager and recent scopes under topic
2. Extract SQL builder for comment_threads into last_user_nickname under comment_thread
3. Look into extracting user_link into a UserDecorator
4. Use Slim! 🙂