1 files changed, 123 insertions, 56 deletions

diff --git a/activemodel/lib/active_model/dirty.rb b/activemodel/lib/active_model/dirty.rb
index 943db0ab52..eaf8dfb223 100644
--- a/activemodel/lib/active_model/dirty.rb
+++ b/activemodel/lib/active_model/dirty.rb
@@ -2,6 +2,7 @@
 
 require "active_support/hash_with_indifferent_access"
 require "active_support/core_ext/object/duplicable"
+require "active_model/attribute_mutation_tracker"
 
 module ActiveModel
   # == Active \Model \Dirty
@@ -130,6 +131,26 @@ module ActiveModel
       attribute_method_affix prefix: "restore_", suffix: "!"
     end
 
+    def initialize_dup(other) # :nodoc:
+      super
+      if self.class.respond_to?(:_default_attributes)
+        @attributes = self.class._default_attributes.map do |attr|
+          attr.with_value_from_user(@attributes.fetch_value(attr.name))
+        end
+      end
+      @mutations_from_database = nil
+    end
+
+    def changes_applied # :nodoc:
+      unless defined?(@attributes)
+        @previously_changed = changes
+      end
+      @mutations_before_last_save = mutations_from_database
+      @attributes_changed_by_setter = ActiveSupport::HashWithIndifferentAccess.new
+      forget_attribute_assignments
+      @mutations_from_database = nil
+    end
+
     # Returns +true+ if any of the attributes have unsaved changes, +false+ otherwise.
     #
     #   person.changed? # => false
@@ -148,6 +169,60 @@ module ActiveModel
       changed_attributes.keys
     end
 
+    # Handles <tt>*_changed?</tt> for +method_missing+.
+    def attribute_changed?(attr, from: OPTION_NOT_GIVEN, to: OPTION_NOT_GIVEN) # :nodoc:
+      !!changes_include?(attr) &&
+        (to == OPTION_NOT_GIVEN || to == _read_attribute(attr)) &&
+        (from == OPTION_NOT_GIVEN || from == changed_attributes[attr])
+    end
+
+    # Handles <tt>*_was</tt> for +method_missing+.
+    def attribute_was(attr) # :nodoc:
+      attribute_changed?(attr) ? changed_attributes[attr] : _read_attribute(attr)
+    end
+
+    # Handles <tt>*_previously_changed?</tt> for +method_missing+.
+    def attribute_previously_changed?(attr) #:nodoc:
+      previous_changes_include?(attr)
+    end
+
+    # Restore all previous data of the provided attributes.
+    def restore_attributes(attributes = changed)
+      attributes.each { |attr| restore_attribute! attr }
+    end
+
+    # Clears all dirty data: current changes and previous changes.
+    def clear_changes_information
+      @previously_changed = ActiveSupport::HashWithIndifferentAccess.new
+      @mutations_before_last_save = nil
+      @attributes_changed_by_setter = ActiveSupport::HashWithIndifferentAccess.new
+      forget_attribute_assignments
+      @mutations_from_database = nil
+    end
+
+    def clear_attribute_changes(attr_names)
+      attributes_changed_by_setter.except!(*attr_names)
+      attr_names.each do |attr_name|
+        clear_attribute_change(attr_name)
+      end
+    end
+
+    # Returns a hash of the attributes with unsaved changes indicating their original
+    # values like <tt>attr => original value</tt>.
+    #
+    #   person.name # => "bob"
+    #   person.name = 'robert'
+    #   person.changed_attributes # => {"name" => "bob"}
+    def changed_attributes
+      # This should only be set by methods which will call changed_attributes
+      # multiple times when it is known that the computed value cannot change.
+      if defined?(@cached_changed_attributes)
+        @cached_changed_attributes
+      else
+        attributes_changed_by_setter.reverse_merge(mutations_from_database.changed_values).freeze
+      end
+    end
+
     # Returns a hash of changed attributes indicating their original
     # and new values like <tt>attr => [original value, new value]</tt>.
     #
@@ -155,7 +230,9 @@ module ActiveModel
     #   person.name = 'bob'
     #   person.changes # => { "name" => ["bill", "bob"] }
     def changes
-      ActiveSupport::HashWithIndifferentAccess[changed.map { |attr| [attr, attribute_change(attr)] }]
+      cache_changed_attributes do
+        ActiveSupport::HashWithIndifferentAccess[changed.map { |attr| [attr, attribute_change(attr)] }]
+      end
     end
 
     # Returns a hash of attributes that were changed before the model was saved.
@@ -166,45 +243,51 @@ module ActiveModel
     #   person.previous_changes # => {"name" => ["bob", "robert"]}
     def previous_changes
       @previously_changed ||= ActiveSupport::HashWithIndifferentAccess.new
+      @previously_changed.merge(mutations_before_last_save.changes)
     end
 
-    # Returns a hash of the attributes with unsaved changes indicating their original
-    # values like <tt>attr => original value</tt>.
-    #
-    #   person.name # => "bob"
-    #   person.name = 'robert'
-    #   person.changed_attributes # => {"name" => "bob"}
-    def changed_attributes
-      @changed_attributes ||= ActiveSupport::HashWithIndifferentAccess.new
+    def attribute_changed_in_place?(attr_name) # :nodoc:
+      mutations_from_database.changed_in_place?(attr_name)
     end
 
-    # Handles <tt>*_changed?</tt> for +method_missing+.
-    def attribute_changed?(attr, from: OPTION_NOT_GIVEN, to: OPTION_NOT_GIVEN) # :nodoc:
-      !!changes_include?(attr) &&
-        (to == OPTION_NOT_GIVEN || to == _read_attribute(attr)) &&
-        (from == OPTION_NOT_GIVEN || from == changed_attributes[attr])
-    end
+    private
+      def clear_attribute_change(attr_name)
+        mutations_from_database.forget_change(attr_name)
+      end
 
-    # Handles <tt>*_was</tt> for +method_missing+.
-    def attribute_was(attr) # :nodoc:
-      attribute_changed?(attr) ? changed_attributes[attr] : _read_attribute(attr)
-    end
+      def mutations_from_database
+        unless defined?(@mutations_from_database)
+          @mutations_from_database = nil
+        end
+        @mutations_from_database ||= if defined?(@attributes)
+          ActiveModel::AttributeMutationTracker.new(@attributes)
+        else
+          NullMutationTracker.instance
+        end
+      end
 
-    # Handles <tt>*_previously_changed?</tt> for +method_missing+.
-    def attribute_previously_changed?(attr) #:nodoc:
-      previous_changes_include?(attr)
-    end
+      def forget_attribute_assignments
+        @attributes = @attributes.map(&:forgetting_assignment) if defined?(@attributes)
+      end
 
-    # Restore all previous data of the provided attributes.
-    def restore_attributes(attributes = changed)
-      attributes.each { |attr| restore_attribute! attr }
-    end
+      def mutations_before_last_save
+        @mutations_before_last_save ||= ActiveModel::NullMutationTracker.instance
+      end
 
-    private
+      def cache_changed_attributes
+        @cached_changed_attributes = changed_attributes
+        yield
+      ensure
+        clear_changed_attributes_cache
+      end
+
+      def clear_changed_attributes_cache
+        remove_instance_variable(:@cached_changed_attributes) if defined?(@cached_changed_attributes)
+      end
 
       # Returns +true+ if attr_name is changed, +false+ otherwise.
       def changes_include?(attr_name)
-        attributes_changed_by_setter.include?(attr_name)
+        attributes_changed_by_setter.include?(attr_name) || mutations_from_database.changed?(attr_name)
       end
       alias attribute_changed_by_setter? changes_include?
 
@@ -214,18 +297,6 @@ module ActiveModel
         previous_changes.include?(attr_name)
       end
 
-      # Removes current changes and makes them accessible through +previous_changes+.
-      def changes_applied # :doc:
-        @previously_changed = changes
-        @changed_attributes = ActiveSupport::HashWithIndifferentAccess.new
-      end
-
-      # Clears all dirty data: current changes and previous changes.
-      def clear_changes_information # :doc:
-        @previously_changed = ActiveSupport::HashWithIndifferentAccess.new
-        @changed_attributes = ActiveSupport::HashWithIndifferentAccess.new
-      end
-
       # Handles <tt>*_change</tt> for +method_missing+.
       def attribute_change(attr)
         [changed_attributes[attr], _read_attribute(attr)] if attribute_changed?(attr)
@@ -238,15 +309,16 @@ module ActiveModel
 
       # Handles <tt>*_will_change!</tt> for +method_missing+.
       def attribute_will_change!(attr)
-        return if attribute_changed?(attr)
+        unless attribute_changed?(attr)
+          begin
+            value = _read_attribute(attr)
+            value = value.duplicable? ? value.clone : value
+          rescue TypeError, NoMethodError
+          end
 
-        begin
-          value = _read_attribute(attr)
-          value = value.duplicable? ? value.clone : value
-        rescue TypeError, NoMethodError
+          set_attribute_was(attr, value)
         end
-
-        set_attribute_was(attr, value)
+        mutations_from_database.force_change(attr)
       end
 
       # Handles <tt>restore_*!</tt> for +method_missing+.
@@ -257,18 +329,13 @@ module ActiveModel
         end
       end
 
-      # This is necessary because `changed_attributes` might be overridden in
-      # other implementations (e.g. in `ActiveRecord`)
-      alias_method :attributes_changed_by_setter, :changed_attributes # :nodoc:
+      def attributes_changed_by_setter
+        @attributes_changed_by_setter ||= ActiveSupport::HashWithIndifferentAccess.new
+      end
 
       # Force an attribute to have a particular "before" value
       def set_attribute_was(attr, old_value)
         attributes_changed_by_setter[attr] = old_value
       end
-
-      # Remove changes information for the provided attributes.
-      def clear_attribute_changes(attributes) # :doc:
-        attributes_changed_by_setter.except!(*attributes)
-      end
   end
 end