diff --git a/Gemfile b/Gemfile
index b6dadb1e..b281e1aa 100644
--- a/Gemfile
+++ b/Gemfile
@@ -10,7 +10,7 @@ if Gem::Version.new(Bundler::VERSION) < Gem::Version.new('1.8.4')
 end
 
 # as web framework
-gem 'rails', '~> 5.1.0'
+gem 'rails', '~> 5.2.3'
 
 # Use Puma as the app server
 gem 'puma', '~> 3.0'
diff --git a/Gemfile.lock b/Gemfile.lock
index 7d5a65b8..6928fb8d 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -13,25 +13,25 @@ GEM
   remote: https://rails-assets.org/
   specs:
     Ascii85 (1.0.3)
-    actioncable (5.1.7)
-      actionpack (= 5.1.7)
+    actioncable (5.2.3)
+      actionpack (= 5.2.3)
       nio4r (~> 2.0)
-      websocket-driver (~> 0.6.1)
-    actionmailer (5.1.7)
-      actionpack (= 5.1.7)
-      actionview (= 5.1.7)
-      activejob (= 5.1.7)
+      websocket-driver (>= 0.6.1)
+    actionmailer (5.2.3)
+      actionpack (= 5.2.3)
+      actionview (= 5.2.3)
+      activejob (= 5.2.3)
       mail (~> 2.5, >= 2.5.4)
       rails-dom-testing (~> 2.0)
-    actionpack (5.1.7)
-      actionview (= 5.1.7)
-      activesupport (= 5.1.7)
+    actionpack (5.2.3)
+      actionview (= 5.2.3)
+      activesupport (= 5.2.3)
       rack (~> 2.0)
       rack-test (>= 0.6.3)
       rails-dom-testing (~> 2.0)
       rails-html-sanitizer (~> 1.0, >= 1.0.2)
-    actionview (5.1.7)
-      activesupport (= 5.1.7)
+    actionview (5.2.3)
+      activesupport (= 5.2.3)
       builder (~> 3.1)
       erubi (~> 1.4)
       rails-dom-testing (~> 2.0)
@@ -41,16 +41,20 @@ GEM
       activemodel (>= 4.1, < 6)
       case_transform (>= 0.2)
       jsonapi-renderer (>= 0.1.1.beta1, < 0.3)
-    activejob (5.1.7)
-      activesupport (= 5.1.7)
+    activejob (5.2.3)
+      activesupport (= 5.2.3)
       globalid (>= 0.3.6)
-    activemodel (5.1.7)
-      activesupport (= 5.1.7)
-    activerecord (5.1.7)
-      activemodel (= 5.1.7)
-      activesupport (= 5.1.7)
-      arel (~> 8.0)
-    activesupport (5.1.7)
+    activemodel (5.2.3)
+      activesupport (= 5.2.3)
+    activerecord (5.2.3)
+      activemodel (= 5.2.3)
+      activesupport (= 5.2.3)
+      arel (>= 9.0)
+    activestorage (5.2.3)
+      actionpack (= 5.2.3)
+      activerecord (= 5.2.3)
+      marcel (~> 0.3.1)
+    activesupport (5.2.3)
       concurrent-ruby (~> 1.0, >= 1.0.2)
       i18n (>= 0.7, < 2)
       minitest (~> 5.1)
@@ -72,7 +76,7 @@ GEM
       railties (>= 4.0)
     archive-zip (0.12.0)
       io-like (~> 0.3.0)
-    arel (8.0.0)
+    arel (9.0.0)
     ast (2.4.0)
     autoprefixer-rails (9.6.0)
       execjs
@@ -273,6 +277,8 @@ GEM
     lumberjack (1.0.12)
     mail (2.7.1)
       mini_mime (>= 0.1.1)
+    marcel (0.3.3)
+      mimemagic (~> 0.3.2)
     method_source (0.8.2)
     mime-types (3.2.2)
       mime-types-data (~> 3.2015)
@@ -381,17 +387,18 @@ GEM
       ruby-openid (>= 2.1.8)
     rack-test (1.1.0)
       rack (>= 1.0, < 3)
-    rails (5.1.7)
-      actioncable (= 5.1.7)
-      actionmailer (= 5.1.7)
-      actionpack (= 5.1.7)
-      actionview (= 5.1.7)
-      activejob (= 5.1.7)
-      activemodel (= 5.1.7)
-      activerecord (= 5.1.7)
-      activesupport (= 5.1.7)
+    rails (5.2.3)
+      actioncable (= 5.2.3)
+      actionmailer (= 5.2.3)
+      actionpack (= 5.2.3)
+      actionview (= 5.2.3)
+      activejob (= 5.2.3)
+      activemodel (= 5.2.3)
+      activerecord (= 5.2.3)
+      activestorage (= 5.2.3)
+      activesupport (= 5.2.3)
       bundler (>= 1.3.0)
-      railties (= 5.1.7)
+      railties (= 5.2.3)
       sprockets-rails (>= 2.0.0)
     rails-assets-bootstrap (3.3.6)
       rails-assets-jquery (>= 1.9.1, < 3)
@@ -425,12 +432,12 @@ GEM
     rails-i18n (5.1.3)
       i18n (>= 0.7, < 2)
       railties (>= 5.0, < 6)
-    railties (5.1.7)
-      actionpack (= 5.1.7)
-      activesupport (= 5.1.7)
+    railties (5.2.3)
+      actionpack (= 5.2.3)
+      activesupport (= 5.2.3)
       method_source
       rake (>= 0.8.7)
-      thor (>= 0.18.1, < 2.0)
+      thor (>= 0.19.0, < 2.0)
     rainbow (3.0.0)
     rake (12.3.2)
     rb-fsevent (0.10.3)
@@ -596,7 +603,7 @@ GEM
       addressable (>= 2.3.6)
       crack (>= 0.3.2)
       hashdiff
-    websocket-driver (0.6.5)
+    websocket-driver (0.7.0)
       websocket-extensions (>= 0.1.0)
     websocket-extensions (0.1.3)
     whenever (0.10.0)
@@ -675,7 +682,7 @@ DEPENDENCIES
   prawn-qrcode
   prawn-rails
   puma (~> 3.0)
-  rails (~> 5.1.0)
+  rails (~> 5.2.3)
   rails-assets-bootstrap-markdown!
   rails-assets-bootstrap-select!
   rails-assets-date.format!
diff --git a/app/models/.lodging.rb.swp b/app/models/.lodging.rb.swp
new file mode 100644
index 00000000..70c3567d
Binary files /dev/null and b/app/models/.lodging.rb.swp differ
diff --git a/app/models/conference.rb b/app/models/conference.rb
index ca37e6d0..be3c36ad 100644
--- a/app/models/conference.rb
+++ b/app/models/conference.rb
@@ -115,7 +115,7 @@ class Conference < ApplicationRecord
   # Delete all EventSchedules that are not in the hours range
   # After the conference has been successfully updated
   def delete_event_schedules
-    if start_hour_changed? || end_hour_changed?
+    if saved_change_to_start_hour? || saved_change_to_end_hour?
       event_schedules = program.event_schedules.select do |event_schedule|
         event_schedule.start_time.hour < start_hour ||
         event_schedule.end_time.hour > end_hour ||
@@ -642,7 +642,7 @@ class Conference < ApplicationRecord
   def notify_on_dates_changed?
     return false unless email_settings.send_on_conference_dates_updated
     # do not notify unless one of the dates changed
-    return false unless start_date_changed? || end_date_changed?
+    return false unless saved_change_to_start_date? || saved_change_to_end_date?
 
     # do not notify unless the mail content is set up
     (email_settings.conference_dates_updated_subject.present? && email_settings.conference_dates_updated_body.present?)
@@ -659,7 +659,7 @@ class Conference < ApplicationRecord
     # do not notify unless we allow a registration
     return false unless registration_period
     # do not notify unless one of the dates changed
-    return false unless registration_period.start_date_changed? || registration_period.end_date_changed?
+    return false unless registration_period.saved_change_to_start_date? || registration_period.saved_change_to_end_date?
 
     # do not notify unless the mail content is set up
     (email_settings.conference_registration_dates_updated_subject.present? && email_settings.conference_registration_dates_updated_body.present?)
diff --git a/app/models/program.rb b/app/models/program.rb
index 0dadee15..8db24c6c 100644
--- a/app/models/program.rb
+++ b/app/models/program.rb
@@ -72,8 +72,8 @@ class Program < ApplicationRecord
 
   after_create :create_event_types
   after_create :create_difficulty_levels
-  after_save :unschedule_unfit_events, if: :schedule_interval_changed?
-  after_save :normalize_event_types_length, if: :schedule_interval_changed?
+  after_save :unschedule_unfit_events, if: :saved_change_to_schedule_interval?
+  after_save :normalize_event_types_length, if: :saved_change_to_schedule_interval?
   validate :check_languages_format
 
   # Returns all event_schedules for the selected schedule ordered by start_time
diff --git a/app/models/survey_question.rb b/app/models/survey_question.rb
index 7f3f7750..e1cb0427 100644
--- a/app/models/survey_question.rb
+++ b/app/models/survey_question.rb
@@ -10,7 +10,7 @@ class SurveyQuestion < ActiveRecord::Base
   ICONS = { boolean: 'dot-circle-o', choice: 'check-square-o', string: 'edit', text: 'align-left', datetime: 'clock-o', numeric: 'slack' }.freeze
 
   validates :title, presence: true
-  validates :possible_answers, :max_choices, :min_choices, presence: true, if: 'choice?'
+  validates :possible_answers, :max_choices, :min_choices, presence: true, if: :choice?
   validates :min_choices, numericality: { greater_than_or_equal_to: 1 }, allow_blank: true
   validates :max_choices, numericality: { greater_than_or_equal_to: 1 }, allow_blank: true
 
diff --git a/app/models/venue.rb b/app/models/venue.rb
index 592279ad..5abdcf96 100644
--- a/app/models/venue.rb
+++ b/app/models/venue.rb
@@ -37,7 +37,7 @@ class Venue < ApplicationRecord
   def notify_on_venue_changed?
     return false unless conference.try(:email_settings).try(:send_on_venue_updated)
     # do not notify unless the address changed
-    return false unless name_changed? || street_changed? || city_changed? || country_changed?
+    return false unless saved_change_to_name? || saved_change_to_street? || saved_change_to_city? || saved_change_to_country?
 
     # do not notify unless the mail content is set up
     (!conference.email_settings.venue_updated_subject.blank? && !conference.email_settings.venue_updated_body.blank?)
diff --git a/app/views/admin/lodgings/index.html.haml b/app/views/admin/lodgings/index.html.haml
index c2e011f9..67b5e3df 100644
--- a/app/views/admin/lodgings/index.html.haml
+++ b/app/views/admin/lodgings/index.html.haml
@@ -16,9 +16,9 @@
           - else
             - if lodging.website_link.present?
               = link_to(lodging.website_link, class: 'thumbnail') do
-                = image_tag lodging.picture.thumb, class: 'img-responsive img-lodging'
+                = image_tag lodging.picture.thumb.url, class: 'img-responsive img-lodging'
             - else
-              = image_tag lodging.picture.thumb, class: 'img-responsive img-lodging'
+              = image_tag lodging.picture.thumb.url, class: 'img-responsive img-lodging'
           .caption
             %h3.text-center
               = lodging.name