MONGOID-5899 Write conflict error when accessing embedded documents via [] operator after direct DB update

lib/mongoid/attributes.rb

@@ -104,7 +104,8 @@ def read_attribute(name)
     # @api private
     def process_raw_attribute(name, raw, field)
       value = field ? field.demongoize(raw) : raw
-      attribute_will_change!(name) if value.resizable?
+      is_relation = relations.key?(name)
+      attribute_will_change!(name) if value.resizable? && !is_relation
       value
     end
 

spec/mongoid/attributes_spec.rb

@@ -2722,7 +2722,23 @@
     end
   end
 
-  context "when modifiying a set referenced with the [] notation" do
+  context "when accessing an embedded document with the attribute accessor" do
+    let(:band) { Band.create! }
+
+    before do
+      Band.where(id: band.id).update_all({
+        :$push => {records: { _id: BSON::ObjectId.new }}
+      })
+    end
+
+    it "does not throw a conflicting update error" do
+      b1 = Band.find(band.id)
+      b1[:records].is_a?(Array).should be true
+      expect { b1.save! }.not_to raise_error
+    end
+  end
+
+  context "when modifying a set referenced with the [] notation" do
     let(:catalog) { Catalog.create!(set_field: [ 1 ].to_set) }
 
     before do