[#780] using a changing cache key to avoid the need for explicit cache invalidation

This should work on all cache stores, since only the basic cache operations fetch and delete are used. The methods clear_cache and check_cache can no longer be supported. To sweep the whole cache Rails.cache.clear may be used. To invalidate the Settings only, you may use Setting.first.try(:touch).

app/models/setting.rb

@@ -97,13 +97,13 @@ class Setting < ActiveRecord::Base
 
   # Returns the value of the setting named name
   def self.[](name)
-    Marshal.load(Rails.cache.fetch("chiliproject/setting/#{name}") {Marshal.dump(find_or_default(name).value)})
+    Marshal.load(Rails.cache.fetch(self.cache_key(name)) {Marshal.dump(find_or_default(name).value)})
   end
 
   def self.[]=(name, v)
     setting = find_or_default(name)
     setting.value = (v ? v : "")
-    Rails.cache.delete "chiliproject/setting/#{name}"
+    Rails.cache.delete self.cache_key(name)
     setting.save
     setting.value
   end
@@ -137,23 +137,19 @@ class Setting < ActiveRecord::Base
     Object.const_defined?(:OpenID) && self[:openid].to_i > 0
   end
 
-  # Checks if settings have changed since the values were read
-  # and clears the cache hash if it's the case
-  # Called once per request
+  # Deprecation Warning: This method is no longer available. There is no
+  # replacement.
   def self.check_cache
-    settings_updated_on = Setting.maximum(:updated_on)
-    cache_cleared_on = Rails.cache.read('chiliproject/setting-cleared_on')
-    cache_cleared_on = cache_cleared_on ? Marshal.load(cache_cleared_on) : Time.now
-    if settings_updated_on && cache_cleared_on <= settings_updated_on
-      clear_cache
-    end
+    ActiveSupport::Deprecation.warn "The Setting.check_cache method is " +
+      "deprecated and will be removed in the future. There should be no " +
+      "replacement for this functionality needed."
   end
 
   # Clears all of the Setting caches
   def self.clear_cache
-    Rails.cache.delete_matched( /^chiliproject\/setting\/.+$/ )
-    Rails.cache.write('chiliproject/setting-cleared_on', Marshal.dump(Time.now))
-    logger.info 'Settings cache cleared.' if logger
+    ActiveSupport::Deprecation.warn "The Setting.clear_cache method is " +
+      "deprecated and will be removed in the future. There should be no " +
+      "replacement for this functionality needed."
   end
 
 private
@@ -165,4 +161,8 @@ private
     setting = find_by_name(name)
     setting ||= new(:name => name, :value => @@available_settings[name]['default']) if @@available_settings.has_key? name
   end
+
+  def self.cache_key(name)
+    "chiliproject/setting/#{Setting.maximum(:updated_on).to_i}/#{name}"
+  end
 end