Rails: Grouping the records by group_by method

Many times we come across such situations where we need to group records, like when we want to display grouped messages, email, alerts .etc based on date or time. Here is the simple code which provides a significant use of group_by method.

Controller Part

class MessagesController < ApplicationController

 def index
   @message = Message.all

   #Retrives all messages and divides into two groups todays messages and other messages
   @grouped_messages = @message.group_by{ |t| t.created_at.to_date == DateTime.now.to_date }

   if @grouped_messages[false].present?
     #Create month wise groups of messages      
     @month_wise_sorted_alerts  = @grouped_messages[false].group_by{ |t| t.created_at.month}
   end    
 end
end

@message.group_by{ |t| t.created_at.to_date == DateTime.now.to_date }

The above line return us the messages in Ordered Hash with two keys true and false on which the messages which are of today's date will be values in true key and others will be values in false.

@grouped_messages[false].group_by{ |t| t.created_at.month }

Above line will provide us the monthwise sorting of the messsages. It will create the Ordered Hash with keys as the month numbers and values as the messages according to their month numbers.

View Part

<h1>Messages</h1>

<!-- Todays messages -->

<% if @grouped_messages.present? && @grouped_messages[true].present? %>
 <h3> Today </h3>
 <% @grouped_messages[true].each do |msg| %>
   <%= msg.content %>
   <%= msg.created_at.strftime('%I:%M %p') %>
   <br />
 <% end %>
 <br />
<% end %>


<!-- Month wise sorted messages -->

<% if @month_wise_sorted_alerts.present? %>
 <% @month_wise_sorted_alerts.each do |hash_elements|%>
 <h3> <%= Date::MONTHNAMES[hash_elements.first] %> </h3>
 <% hash_elements.last.each do |msg| %>
   <%= msg.content %>
   <%= msg.created_at.strftime('%b %d') %>
   <br />
 <% end %>
 <br />
 <% end %>
<% end %>

We can use rails helper to get the month name Date::MONTHNAMES[--month_number--] to get the name of the month in the view.

You can also use the gem https://github.com/ankane/groupdate to get more functionality.

References:

• http://apidock.com/rails/Enumerable/group_by