apply_filter and apply_sort respects :delegate option of attribute

lib/jsonapi/active_record_accessor.rb

@@ -225,6 +225,7 @@ def apply_sort(records, order_options, context = {})
               order_by_query = "#{associations.last.name}_sorting.#{column_name} #{direction}"
               records = records.joins(joins_query).order(order_by_query)
             else
+              field = _resource_klass._attribute_delegated_name(field)
               records = records.order(field => direction)
             end
           end
@@ -274,6 +275,7 @@ def apply_filter(records, filter, value, options = {})
             records.where("#{_resource_klass._relationships[filter].table_name}.#{_resource_klass._relationships[filter].primary_key}" => value)
           end
         else
+          filter = _resource_klass._attribute_delegated_name(filter)
           records.where(filter => value)
         end
       end

lib/jsonapi/resource.rb

@@ -755,6 +755,10 @@ def _attribute_options(attr)
         default_attribute_options.merge(@_attributes[attr])
       end
 
+      def _attribute_delegated_name(attr)
+        @_attributes.fetch(attr.to_sym, {}).fetch(:delegate, attr)
+      end
+
       def _updatable_attributes
         _attributes.map { |key, options| key unless options[:readonly] }.compact
       end

test/controllers/controller_test.rb

@@ -3757,3 +3757,26 @@ def test_complex_includes_nested_things_secondary_users
     assert_equal '2',  json_response['included'][1]['relationships']['things']['data'][0]['id']
   end
 end
+
+class BlogPostsControllerTest < ActionController::TestCase
+  def test_filter_by_delegated_attribute
+    assert_cacheable_get :index, params: {filter: {name: 'some title'}}
+    assert_response :success
+  end
+
+  def test_sorting_by_delegated_attribute
+    assert_cacheable_get :index, params: {sort: 'name'}
+    assert_response :success
+  end
+
+  def test_fields_with_delegated_attribute
+    original_config = JSONAPI.configuration.dup
+    JSONAPI.configuration.json_key_format = :underscored_key
+
+    assert_cacheable_get :index, params: {fields: {blog_posts: 'name'}}
+    assert_response :success
+    assert_equal ['name'], json_response['data'].first['attributes'].keys
+  ensure
+    JSONAPI.configuration = original_config
+  end
+end

test/fixtures/active_record.rb

@@ -1801,6 +1801,24 @@ class FlatPostResource < JSONAPI::Resource
 class FlatPostsController < JSONAPI::ResourceController
 end
 
+class BlogPost < ActiveRecord::Base
+  self.table_name = 'posts'
+end
+
+class BlogPostsController < JSONAPI::ResourceController
+
+end
+
+class BlogPostResource < JSONAPI::Resource
+  model_name 'BlogPost', add_model_hint: false
+  model_hint model: 'BlogPost', resource: BlogPostResource
+
+  attribute :name, :delegate => :title
+  attribute :body
+
+  filter :name
+end
+
 # CustomProcessors
 class Api::V4::BookProcessor < JSONAPI::Processor
   after_find do

test/test_helper.rb

@@ -252,6 +252,7 @@ class CatResource < JSONAPI::Resource
   jsonapi_resources :cars
   jsonapi_resources :boats
   jsonapi_resources :flat_posts
+  jsonapi_resources :blog_posts
 
   jsonapi_resources :books
   jsonapi_resources :authors