GRN2-xx: Switch the relation between users and roles to make queries cleaner and faster (#1299)

* First steps

* Fixes in account creation flow

* Fixed most testcases

* more test fixes

* Fixed more test cases

* Passing tests and rubocop

* Added rake task to remove rooms

db/migrate/20190314152108_rolify_create_roles.rb

@@ -19,7 +19,7 @@ class RolifyCreateRoles < ActiveRecord::Migration[5.0]
     add_index(:users_roles, [:user_id, :role_id])
 
     User.all.each do |user|
-      user.add_role(:user) if user.roles.blank?
+      user.set_role(:user) if user.roles.blank?
     end
   end
 end

db/migrate/20200413150518_add_role_id_to_users.rb

@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+class MigrationProduct < ActiveRecord::Base
+  self.table_name = :users
+end
+
+class SubMigrationProduct < ActiveRecord::Base
+  self.table_name = :roles
+end
+
+class AddRoleIdToUsers < ActiveRecord::Migration[5.2]
+  def change
+    reversible do |dir|
+      dir.up do
+        add_reference :users, :role, index: true
+
+        MigrationProduct.where(role_id: nil).each do |user|
+          highest_role = SubMigrationProduct.joins("INNER JOIN users_roles ON users_roles.role_id = roles.id")
+                                            .where("users_roles.user_id = '#{user.id}'").min_by(&:priority).id
+          user.update_attributes(role_id: highest_role) unless highest_role.nil?
+        end
+      end
+
+      dir.down do
+        remove_reference :users, :role, index: true
+      end
+    end
+  end
+end