Allow methods from ancestors of the entity

.rubocop_todo.yml

@@ -12,7 +12,7 @@ Metrics/AbcSize:
 # Offense count: 2
 # Configuration parameters: CountComments.
 Metrics/ClassLength:
-  Max: 202
+  Max: 206
 
 # Offense count: 3
 Metrics/CyclomaticComplexity:

CHANGELOG.md

@@ -1,6 +1,7 @@
 0.5.2 (Next)
 ============
 
+* [#238](https://github.com/ruby-grape/grape-entity/pull/238): `#delegate_attribute` delegates to methods included from inherited entities - [@anakinj](https://github.com/anakinj).
 * [#215](https://github.com/ruby-grape/grape-entity/pull/217): Fix: `#delegate_attribute` no longer delegates to methods included with `Kernel` - [@maltoe](https://github.com/maltoe).
 * [#219](https://github.com/ruby-grape/grape-entity/pull/219): Fix: double pass options in serializable_hash - [@sbatykov](https://github.com/sbatykov).
 * [#226](https://github.com/ruby-grape/grape-entity/pull/226): Added fetch method to fetch from opts_hash - [@alanjcfs](https://github.com/alanjcfs).

lib/grape_entity/entity.rb

@@ -478,13 +478,18 @@ def value_for(key, options = Options.new)
     end
 
     def delegate_attribute(attribute)
-      if respond_to?(attribute, true) && method(attribute).owner == self.class
+      if respond_to?(attribute, true) && entity_method?(attribute)
         send(attribute)
       else
         delegator.delegate(attribute)
       end
     end
 
+    def entity_method?(attribute)
+      method_owner = method(attribute).owner
+      self.class == method_owner || self.class.ancestors[0..self.class.ancestors.find_index(Grape::Entity) - 1].include?(method_owner)
+    end
+
     alias_method :as_json, :serializable_hash
 
     def to_json(options = {})

spec/grape_entity/entity_spec.rb

@@ -1561,6 +1561,26 @@ class DelegatingEntity < Grape::Entity
         expect(rep.value_for(:system)).to eq 'System'
       end
 
+      it 'allows methods to be inherited' do
+        module EntitySpec
+          class ParentEntity < Grape::Entity
+            expose :parent
+
+            private
+
+            def parent
+              'I am the parent'
+            end
+          end
+
+          class ChildEntity < ParentEntity; end
+        end
+
+        foo = double('Foo', value: 'test')
+        rep = EntitySpec::ChildEntity.new foo
+        expect(rep.value_for(:parent)).to eq 'I am the parent'
+      end
+
       context 'using' do
         before do
           module EntitySpec