avoid overwriting default setting value

app/models/setting.rb

@@ -29,6 +29,9 @@
 #++
 
 class Setting < ApplicationRecord
+  extend Callbacks
+  extend Aliases
+
   DATE_FORMATS = [
     '%Y-%m-%d',
     '%d/%m/%Y',
@@ -338,8 +341,4 @@ class Setting < ApplicationRecord
       value
     end
   end
-
-  extend Callbacks
-
-  extend Aliases
 end

db/migrate/20190618115620_fix_available_languages.rb

@@ -1,12 +1,14 @@
 class FixAvailableLanguages < ActiveRecord::Migration[5.2]
   def up
-    Setting.reset_column_information
+    if Setting.exists?(name: 'available_languages')
+      Setting.reset_column_information
 
-    Setting.available_languages = Setting.available_languages.map do |lang|
-      if lang == 'zh'
-        'zh-CN'
-      else
-        lang
+      Setting.available_languages = Setting.available_languages.map do |lang|
+        if lang == 'zh'
+          'zh-CN'
+        else
+          lang
+        end
       end
     end
 
@@ -14,13 +16,15 @@ class FixAvailableLanguages < ActiveRecord::Migration[5.2]
   end
 
   def down
-    Setting.reset_column_information
+    if Setting.exists?(name: 'available_languages')
+      Setting.reset_column_information
 
-    Setting.available_languages = Setting.available_languages.map do |lang|
-      if lang == 'zh-CN'
-        'zh'
-      else
-        lang
+      Setting.available_languages = Setting.available_languages.map do |lang|
+        if lang == 'zh-CN'
+          'zh'
+        else
+          lang
+        end
       end
     end
 

db/migrate/20200903064009_enable_current_project_custom_fields_columns.rb

@@ -1,5 +1,7 @@
 class EnableCurrentProjectCustomFieldsColumns < ActiveRecord::Migration[6.0]
   def up
+    return unless Setting.exists?(name: 'enabled_projects_column')
+
     columns = Setting.enabled_projects_columns
     cf_columns = ProjectCustomField.pluck(:id).map { |id| "cf_#{id}" }