Allow customizable default sort

Author: Lee Richmond

lib/jsonapi_compliable/base.rb

@@ -21,6 +21,10 @@ def default_page_size
       20
     end
 
+    def default_sort
+      'id'
+    end
+
     def jsonapi_scope(scope,
                       filter: true,
                       includes: true,

lib/jsonapi_compliable/scope/sort.rb

@@ -15,7 +15,7 @@ def apply_custom_scope
     private
 
     def sort_param
-      @sort_param ||= (params[:sort] || 'id')
+      @sort_param ||= (params[:sort] || @controller.default_sort)
     end
 
     def direction

spec/sorting_spec.rb

@@ -14,10 +14,13 @@ def index
     Author.create!(first_name: 'Philip')
   end
 
-  it 'defaults sort to id asc' do
+  it 'defaults sort to controller default_sort' do
+    expect(controller).to receive(:default_sort) { 'id' }
     get :index
-    expect(json_ids.length).to eq(2)
     expect(json_ids(true)).to eq(Author.pluck(:id))
+    expect(controller).to receive(:default_sort) { '-id' }
+    get :index
+    expect(json_ids(true)).to eq(Author.pluck(:id).reverse)
   end
 
   context 'when passing sort param' do