allow modifier field to be optional

CHANGELOG.md

@@ -1,6 +1,7 @@
 ### 0.7.1 (Next)
 
 * Your contribution here.
+* [#205](https://github.com/mongoid/mongoid-history/pull/205): Allow modifier field to be optional - [@yads](https://github.com/yads).
 
 ### 0.7.0 (2017/11/14)
 

README.md

@@ -66,8 +66,9 @@ class Post
   # telling Mongoid::History how you want to track changes
   # dynamic fields will be tracked automatically (for MongoId 4.0+ you should include Mongoid::Attributes::Dynamic to your model)
   track_history   :on => [:title, :body],       # track title and body fields only, default is :all
-                  :modifier_field => :modifier, # adds "belongs_to :modifier" to track who made the change, default is :modifier
+                  :modifier_field => :modifier, # adds "belongs_to :modifier" to track who made the change, default is :modifier, set to nil to not create modifier_field
                   :modifier_field_inverse_of => :nil, # adds an ":inverse_of" option to the "belongs_to :modifier" relation, default is not set
+                  :modifier_field_optional => true, # marks the modifier relationship as optional
                   :version_field => :version,   # adds "field :version, :type => Integer" to track current version, default is :version
                   :track_create   =>  false,    # track document creation, default is false
                   :track_update   =>  true,     # track document updates, default is true

lib/mongoid/history/trackable.rb

@@ -12,9 +12,12 @@ def track_history(options = {})
 
           field options[:version_field].to_sym, type: Integer
 
-          belongs_to_modifier_options = { class_name: Mongoid::History.modifier_class_name }
-          belongs_to_modifier_options[:inverse_of] = options[:modifier_field_inverse_of] if options.key?(:modifier_field_inverse_of)
-          belongs_to options[:modifier_field].to_sym, belongs_to_modifier_options
+          unless options[:modifier_field].nil?
+            belongs_to_modifier_options = { class_name: Mongoid::History.modifier_class_name }
+            belongs_to_modifier_options[:inverse_of] = options[:modifier_field_inverse_of] if options.key?(:modifier_field_inverse_of)
+            belongs_to_modifier_options[:optional] = true if options[:modifier_field_optional]
+            belongs_to options[:modifier_field].to_sym, belongs_to_modifier_options
+          end
 
           include MyInstanceMethods
           extend SingletonMethods
@@ -219,11 +222,12 @@ def modified_attributes_for_destroy
         def history_tracker_attributes(action)
           return @history_tracker_attributes if @history_tracker_attributes
 
+          modifier_field = history_trackable_options[:modifier_field]
           @history_tracker_attributes = {
             association_chain: traverse_association_chain,
             scope: related_scope,
-            modifier: send(history_trackable_options[:modifier_field])
           }
+          @history_tracker_attributes[:modifier] = send(modifier_field) if modifier_field
 
           original, modified = transform_changes(modified_attributes_for_action(action))
 
@@ -425,7 +429,12 @@ def tracked_fields
         #
         # @return [ Array < String > ] the list of reserved database field names
         def reserved_tracked_fields
-          @reserved_tracked_fields ||= ['_id', history_trackable_options[:version_field].to_s, "#{history_trackable_options[:modifier_field]}_id"]
+          @reserved_tracked_fields ||= begin
+                                         fields = ['_id', history_trackable_options[:version_field].to_s]
+                                         modifier_field = history_trackable_options[:modifier_field]
+                                         fields << "#{modifier_field}_id" if modifier_field
+                                         fields
+                                       end
         end
 
         def field_formats

lib/mongoid/history/tracker.rb

@@ -50,7 +50,7 @@ def undo_attr(modifier)
         undo_hash = affected.easy_unmerge(modified)
         undo_hash.easy_merge!(original)
         modifier_field = trackable.history_trackable_options[:modifier_field]
-        undo_hash[modifier_field] = modifier
+        undo_hash[modifier_field] = modifier if modifier_field
         (modified.keys - undo_hash.keys).each do |k|
           undo_hash[k] = nil
         end
@@ -61,7 +61,7 @@ def redo_attr(modifier)
         redo_hash = affected.easy_unmerge(original)
         redo_hash.easy_merge!(modified)
         modifier_field = trackable.history_trackable_options[:modifier_field]
-        redo_hash[modifier_field] = modifier
+        redo_hash[modifier_field] = modifier if modifier_field
         localize_keys(redo_hash)
       end
 

spec/unit/trackable_spec.rb

@@ -6,6 +6,12 @@ class MyModel
   field :foo
 end
 
+class MyModelWithNoModifier
+  include Mongoid::Document
+  include Mongoid::History::Trackable
+  field :foo
+end
+
 class MyDynamicModel
   include Mongoid::Document
   include Mongoid::History::Trackable
@@ -31,6 +37,7 @@ class HistoryTracker
     before :all do
       MyModel.track_history
       @persisted_history_options = Mongoid::History.trackable_class_options
+      MyModelWithNoModifier.track_history modifier_field: nil
     end
     before(:each) { Mongoid::History.trackable_class_options = @persisted_history_options }
     let(:expected_option) do
@@ -72,6 +79,12 @@ class HistoryTracker
       expect(MyModel.history_trackable_options).to eq(expected_option)
     end
 
+    context 'modifier_field set to nil' do
+      it 'should not have a modifier relationship' do
+        expect(MyModelWithNoModifier.reflect_on_association(:modifier)).to be_nil
+      end
+    end
+
     describe '#tracked_fields' do
       it 'should return the tracked field list' do
         expect(MyModel.tracked_fields).to eq(regular_fields)
@@ -82,6 +95,10 @@ class HistoryTracker
       it 'should return the protected field list' do
         expect(MyModel.reserved_tracked_fields).to eq(reserved_fields)
       end
+
+      it 'should not include modifier_field if not specified' do
+        expect(MyModelWithNoModifier.reserved_tracked_fields).not_to include('modifier')
+      end
     end
 
     describe '#tracked_fields_for_action' do