Support methods in Dirty API added in Rails 5.2 - name_previously_changed? and name_previous_change

Author: andrykonchin

lib/dynamoid/dirty.rb

@@ -18,6 +18,7 @@ module Dirty
 
     included do
       attribute_method_suffix '_changed?', '_change', '_will_change!', '_was'
+      attribute_method_suffix '_previously_changed?', '_previous_change'
       attribute_method_affix prefix: 'restore_', suffix: '!'
     end
 
@@ -140,6 +141,16 @@ def restore_attributes(attributes = changed)
       attributes.each { |attr| restore_attribute! attr }
     end
 
+    # Handles <tt>*_previously_changed?</tt> for +method_missing+.
+    def attribute_previously_changed?(attr) #:nodoc:
+      previous_changes_include?(attr)
+    end
+
+    # Handles <tt>*_previous_change</tt> for +method_missing+.
+    def attribute_previous_change(attr)
+      previous_changes[attr] if attribute_previously_changed?(attr)
+    end
+
     private
 
       def changes_include?(attr_name)
@@ -185,6 +196,12 @@ def restore_attribute!(attr)
         end
       end
 
+      # Returns +true+ if attr_name were changed before the model was saved,
+      # +false+ otherwise.
+      def previous_changes_include?(attr_name)
+        previous_changes.include?(attr_name)
+      end
+
       # This is necessary because `changed_attributes` might be overridden in
       # other implemntations (e.g. in `ActiveRecord`)
       alias_method :attributes_changed_by_setter, :changed_attributes # :nodoc:

spec/dynamoid/dirty_spec.rb

@@ -103,6 +103,10 @@
         'name' => ['Alex', 'Bob'],
         'updated_at' => ['2019-07-20 00:53:32'.to_datetime, '2019-07-20 20:11:01'.to_datetime]
       )
+
+      obj = model.create(name: 'Alex')
+      # there are also changes for `created_at` and `updated_at` - just don't check them
+      expect(obj.previous_changes).to include('id' => [nil, obj.id], 'name' => [nil, 'Alex'])
     end
 
     it 'returns {} when there were no changes made before saving' do
@@ -153,6 +157,48 @@
     end
   end
 
+  describe '<attribute>_previously_changed?' do
+    it 'returns true if attribute was changed before model was saved' do
+      obj = model.create(name: 'Alex')
+      obj.name = 'Bob'
+      obj.save
+      expect(obj.name_previously_changed?).to eq(true)
+
+      obj = model.create(name: 'Alex')
+      expect(obj.name_previously_changed?).to eq(true)
+    end
+
+    it 'returns false otherwise' do
+      obj = model.create(name: 'Alex')
+      obj = model.find(obj.id)
+      expect(obj.name_previously_changed?).to eq(false)
+
+      obj = model.new(name: 'Alex')
+      expect(obj.name_previously_changed?).to eq(false)
+    end
+  end
+
+  describe '<attribute>_previous_change' do
+    it 'returns an array of old and changed attribute value before the model was saved' do
+      obj = model.create(name: 'Alex')
+      obj.name = 'Bob'
+      obj.save
+      expect(obj.name_previous_change).to eq(['Alex', 'Bob'])
+
+      obj = model.create(name: 'Alex')
+      expect(obj.name_previous_change).to eq([nil, 'Alex'])
+    end
+
+    it 'returns nil when there were no changes made before saving' do
+      obj = model.create(name: 'Alex')
+      obj = model.find(obj.id)
+      expect(obj.name_previous_change).to eq(nil)
+
+      obj = model.new(name: 'Alex')
+      expect(obj.name_previous_change).to eq(nil)
+    end
+  end
+
   describe '<attribute>_will_change!' do
     it 'marks that the attribute is changing' do
       obj = model.create(name: 'Alex')