Always include self, first, last pagination links

lib/active_model_serializers/adapter/json_api/pagination_links.rb

@@ -15,17 +15,18 @@ def initialize(collection, adapter_options)
  JsonApi::PaginationLinks requires a ActiveModelSerializers::SerializationContext.
  Please pass a ':serialization_context' option or
  override CollectionSerializer#paginated? to return 'false'.
-             EOF
+            EOF
           end
         end
 
         def as_json
-          per_page = collection.try(:per_page) || collection.try(:limit_value) || collection.size
-          pages_from.each_with_object({}) do |(key, value), hash|
-            params = query_parameters.merge(page: { number: value, size: per_page }).to_query
-
-            hash[key] = "#{url(adapter_options)}?#{params}"
-          end
+          {
+            self:  location_url,
+            first: first_page_url,
+            prev:  prev_page_url,
+            next:  next_page_url,
+            last:  last_page_url
+          }
         end
 
         protected
@@ -34,25 +35,39 @@ def as_json
 
         private
 
-        def pages_from
-          return {} if collection.total_pages <= FIRST_PAGE
-
-          {}.tap do |pages|
-            pages[:self] = collection.current_page
+        def location_url
+          url_for_page(collection.current_page)
+        end
 
-            unless collection.current_page == FIRST_PAGE
-              pages[:first] = FIRST_PAGE
-              pages[:prev]  = collection.current_page - FIRST_PAGE
-            end
+        def first_page_url
+          url_for_page(1)
+        end
 
-            unless collection.current_page == collection.total_pages
-              pages[:next] = collection.current_page + FIRST_PAGE
-              pages[:last] = collection.total_pages
-            end
+        def last_page_url
+          if collection.total_pages == 0
+            url_for_page(FIRST_PAGE)
+          else
+            url_for_page(collection.total_pages)
           end
         end
 
-        def url(options)
+        def prev_page_url
+          return nil if collection.current_page == FIRST_PAGE
+          url_for_page(collection.current_page - FIRST_PAGE)
+        end
+
+        def next_page_url
+          return nil if collection.total_pages == 0 || collection.current_page == collection.total_pages
+          url_for_page(collection.next_page)
+        end
+
+        def url_for_page(number)
+          params = query_parameters.dup
+          params[:page] = { size: per_page, number: number }
+          "#{url(adapter_options)}?#{params.to_query}"
+        end
+
+        def url(options = {})
           @url ||= options.fetch(:links, {}).fetch(:self, nil) || request_url
         end
 
@@ -63,6 +78,10 @@ def request_url
         def query_parameters
           @query_parameters ||= context.query_parameters
         end
+
+        def per_page
+          @per_page ||= collection.try(:per_page) || collection.try(:limit_value) || collection.size
+        end
       end
     end
   end

test/action_controller/json_api/pagination_test.rb

@@ -58,8 +58,10 @@ def test_render_pagination_links_with_will_paginate
           assert_equal expected_links, response['links']
         end
 
-        def test_render_only_last_and_next_pagination_links
+        def test_render_only_first_last_and_next_pagination_links
           expected_links = { 'self' => "#{WILL_PAGINATE_URI}?page%5Bnumber%5D=1&page%5Bsize%5D=2",
+                             'first' => "#{WILL_PAGINATE_URI}?page%5Bnumber%5D=1&page%5Bsize%5D=2",
+                             'prev' => nil,
                              'next' => "#{WILL_PAGINATE_URI}?page%5Bnumber%5D=2&page%5Bsize%5D=2",
                              'last' => "#{WILL_PAGINATE_URI}?page%5Bnumber%5D=2&page%5Bsize%5D=2" }
           get :render_pagination_using_will_paginate, params: { page: { number: 1, size: 2 } }
@@ -78,28 +80,34 @@ def test_render_pagination_links_with_kaminari
           assert_equal expected_links, response['links']
         end
 
-        def test_render_only_prev_and_first_pagination_links
+        def test_render_only_prev_first_and_last_pagination_links
           expected_links = { 'self' => "#{KAMINARI_URI}?page%5Bnumber%5D=3&page%5Bsize%5D=1",
                              'first' => "#{KAMINARI_URI}?page%5Bnumber%5D=1&page%5Bsize%5D=1",
-                             'prev' => "#{KAMINARI_URI}?page%5Bnumber%5D=2&page%5Bsize%5D=1" }
+                             'prev' => "#{KAMINARI_URI}?page%5Bnumber%5D=2&page%5Bsize%5D=1",
+                             'next' => nil,
+                             'last' => "#{KAMINARI_URI}?page%5Bnumber%5D=3&page%5Bsize%5D=1" }
           get :render_pagination_using_kaminari, params: { page: { number: 3, size: 1 } }
           response = JSON.parse(@response.body)
           assert_equal expected_links, response['links']
         end
 
-        def test_render_only_last_and_next_pagination_links_with_additional_params
+        def test_render_only_first_last_and_next_pagination_links_with_additional_params
           expected_links = { 'self' => "#{WILL_PAGINATE_URI}?page%5Bnumber%5D=1&page%5Bsize%5D=2&teste=additional",
+                             'first' => "#{WILL_PAGINATE_URI}?page%5Bnumber%5D=1&page%5Bsize%5D=2&teste=additional",
+                             'prev' => nil,
                              'next' => "#{WILL_PAGINATE_URI}?page%5Bnumber%5D=2&page%5Bsize%5D=2&teste=additional",
                              'last' => "#{WILL_PAGINATE_URI}?page%5Bnumber%5D=2&page%5Bsize%5D=2&teste=additional" }
           get :render_pagination_using_will_paginate, params: { page: { number: 1, size: 2 }, teste: 'additional' }
           response = JSON.parse(@response.body)
           assert_equal expected_links, response['links']
         end
 
-        def test_render_only_prev_and_first_pagination_links_with_additional_params
+        def test_render_only_prev_first_and_last_pagination_links_with_additional_params
           expected_links = { 'self' => "#{KAMINARI_URI}?page%5Bnumber%5D=3&page%5Bsize%5D=1&teste=additional",
                              'first' => "#{KAMINARI_URI}?page%5Bnumber%5D=1&page%5Bsize%5D=1&teste=additional",
-                             'prev' => "#{KAMINARI_URI}?page%5Bnumber%5D=2&page%5Bsize%5D=1&teste=additional" }
+                             'prev' => "#{KAMINARI_URI}?page%5Bnumber%5D=2&page%5Bsize%5D=1&teste=additional",
+                             'next' => nil,
+                             'last' => "#{KAMINARI_URI}?page%5Bnumber%5D=3&page%5Bsize%5D=1&teste=additional" }
           get :render_pagination_using_kaminari, params: { page: { number: 3, size: 1 }, teste: 'additional' }
           response = JSON.parse(@response.body)
           assert_equal expected_links, response['links']

test/adapter/json_api/pagination_links_test.rb

@@ -54,6 +54,16 @@ def data
           }
         end
 
+        def empty_collection_links
+          {
+            self: "#{URI}?page%5Bnumber%5D=1&page%5Bsize%5D=2",
+            first: "#{URI}?page%5Bnumber%5D=1&page%5Bsize%5D=2",
+            prev: nil,
+            next: nil,
+            last: "#{URI}?page%5Bnumber%5D=1&page%5Bsize%5D=2"
+          }
+        end
+
         def links
           {
             links: {
@@ -71,7 +81,9 @@ def last_page_links
             links: {
               self: "#{URI}?page%5Bnumber%5D=3&page%5Bsize%5D=2",
               first: "#{URI}?page%5Bnumber%5D=1&page%5Bsize%5D=2",
-              prev: "#{URI}?page%5Bnumber%5D=2&page%5Bsize%5D=2"
+              prev: "#{URI}?page%5Bnumber%5D=2&page%5Bsize%5D=2",
+              next: nil,
+              last: "#{URI}?page%5Bnumber%5D=3&page%5Bsize%5D=2"
             }
           }
         end
@@ -108,10 +120,10 @@ def expected_response_with_last_page_pagination_links
           end
         end
 
-        def expected_response_with_no_data_pagination_links
+        def expected_response_with_empty_collection_pagination_links
           {}.tap do |hash|
             hash[:data] = []
-            hash[:links] = {}
+            hash.merge! links: empty_collection_links
           end
         end
 
@@ -139,15 +151,15 @@ def test_pagination_links_when_zero_results_kaminari
 
           adapter = load_adapter(using_kaminari(1), mock_request)
 
-          assert_equal expected_response_with_no_data_pagination_links, adapter.serializable_hash
+          assert_equal expected_response_with_empty_collection_pagination_links, adapter.serializable_hash
         end
 
         def test_pagination_links_when_zero_results_will_paginate
           @array = []
 
           adapter = load_adapter(using_will_paginate(1), mock_request)
 
-          assert_equal expected_response_with_no_data_pagination_links, adapter.serializable_hash
+          assert_equal expected_response_with_empty_collection_pagination_links, adapter.serializable_hash
         end
 
         def test_last_page_pagination_links_using_kaminari