Select thread messages with recursive query

Author: amatsuda

app/controllers/messages_controller.rb

@@ -5,7 +5,10 @@ class MessagesController < ApplicationController
   def index
     if (list_name = params[:list_name])
       @list = List.find_by_name list_name
-      @messages = Message.where(list_id: @list.id).order(:id)
+
+      messages = Message.with_recursive(parent_and_children: [Message.where(list_id: @list.id, parent_id: nil).order(:id).limit(100), Message.joins('inner join parent_and_children on messages.parent_id = parent_and_children.id')])
+        .joins('inner join parent_and_children on parent_and_children.id = messages.id')
+      @messages = compose_tree(messages)
     elsif (query = params[:q])
       search query
 
@@ -47,4 +50,17 @@ def search(query)
     message_where = Message.where('body %> ? AND list_id IN (?)', query, list_ids).order(Arel.sql('body <-> ?', query))
     @messages = message_where.offset(page * PER_PAGE).limit(PER_PAGE)
   end
+
+  def compose_tree(messages)
+    [].tap do |ret|
+      messages.each do |m|
+        if m.parent_id && (parent = messages.detect { it.id == m.parent_id })
+          (parent.children ||= []) << m
+        else
+          ret << m
+        end
+      end
+      ret.sort_by!(&:id)
+    end
+  end
 end