Document#changed? returns true now if only children change:

- Also added Document#children_changed? to determine if any of the
  embedded documents have been altered.
- Fixes #1551

CHANGELOG.md

@@ -33,6 +33,9 @@ For instructions on upgrading to newer versions, visit
 
 * \#1557 Internal strategy class no longer conflicts with models.
 
+* \#1551 Parent documents now return `true` for `Model#changed?` if only child
+  (embedded) documents have changed.
+
 * \#1547 Resetting persisted children from a parent save when new waits until post
   callbacks, mirroring update functionality.
 

lib/mongoid/dirty.rb

@@ -24,7 +24,21 @@ def changed
     #
     # @since 2.4.0
     def changed?
-      changed_attributes.any?
+      changed_attributes.any? || children_changed?
+    end
+
+    # Have any children (embedded documents) of this document changed?
+    #
+    # @example Have any children changed?
+    #   model.children_changed?
+    #
+    # @return [ true, false ] If any children have changed.
+    #
+    # @since 2.4.1
+    def children_changed?
+      _children.any? do |child|
+        child.changed?
+      end
     end
 
     # Get the attribute changes.

lib/mongoid/persistence/operations/update.rb

@@ -42,15 +42,6 @@ class Update
         def persist
           prepare do
             unless updates.empty?
-              # @todo Durran: This is a temporary fix for #791 until we rewrite
-              # the dirty tracking to properly flag a document as changed if
-              # only embedded documents have changed.
-              if document.respond_to?(:updated_at)
-                if document.timestamping? && !document.updated_at_changed?
-                  document.updated_at = Time.now
-                end
-              end
-
               collection.update(selector, updates, options)
               conflicts.each_pair do |key, value|
                 collection.update(selector, { key => value }, options)

spec/functional/mongoid/dirty_spec.rb

@@ -6,6 +6,93 @@
     [ Person, Preference ].each(&:delete_all)
   end
 
+  context "when only embedded documents change" do
+
+    let!(:person) do
+      Person.create(:ssn => "132-11-1111")
+    end
+
+    context "when the child is an embeds one" do
+
+      context "when the child is new" do
+
+        let!(:name) do
+          person.build_name(:first_name => "Gordon", :last_name => "Ramsay")
+        end
+
+        it "flags the parent as changed" do
+          person.should be_changed
+        end
+      end
+
+      context "when the child is modified" do
+
+        let!(:name) do
+          person.create_name(:first_name => "Gordon", :last_name => "Ramsay")
+        end
+
+        before do
+          name.first_name = "G"
+        end
+
+        it "flags the parent as changed" do
+          person.should be_changed
+        end
+      end
+
+      context "when the child is not modified" do
+
+        let!(:name) do
+          person.create_name(:first_name => "Gordon", :last_name => "Ramsay")
+        end
+
+        it "does not flag the parent as changed" do
+          person.should_not be_changed
+        end
+      end
+    end
+
+    context "when the child is an embeds many" do
+
+      context "when a child is new" do
+
+        let!(:address) do
+          person.addresses.build(:street => "jakobstr.")
+        end
+
+        it "flags the parent as changed" do
+          person.should be_changed
+        end
+      end
+
+      context "when a child is modified" do
+
+        let!(:address) do
+          person.addresses.create(:street => "jakobstr.")
+        end
+
+        before do
+          address.city = "Berlin"
+        end
+
+        it "flags the parent as changed" do
+          person.should be_changed
+        end
+      end
+
+      context "when no child is modified" do
+
+        let!(:address) do
+          person.addresses.create(:street => "skalitzerstr.")
+        end
+
+        it "does not flag the parent as changed" do
+          person.should_not be_changed
+        end
+      end
+    end
+  end
+
   context "when changing a hash of hashes" do
 
     let!(:person) do