From e1274b2c14cae41d867093699b5b9bb7f291c427 Mon Sep 17 00:00:00 2001
From: Lucas Hosseini <lucas.hosseini@gmail.com>
Date: Tue, 6 Oct 2015 19:35:09 +0200
Subject: [PATCH] Add support for resource-level JSON API links.

---
 lib/active_model/serializer.rb                | 14 ++++++-
 .../serializer/adapter/json_api.rb            | 23 ++++++++++--
 test/adapter/json_api/links_test.rb           | 37 +++++++++++++++++++
 3 files changed, 69 insertions(+), 5 deletions(-)
 create mode 100644 test/adapter/json_api/links_test.rb

diff --git a/lib/active_model/serializer.rb b/lib/active_model/serializer.rb
index 643167a77..21aec757f 100644
--- a/lib/active_model/serializer.rb
+++ b/lib/active_model/serializer.rb
@@ -50,6 +50,10 @@ def self.type(type)
       self._type = type
     end
 
+    def self.links(&block)
+      self._links_block = block
+    end
+
     def self.attributes(*attrs)
       attrs = attrs.first if attrs.first.class == Array
 
@@ -121,8 +125,9 @@ def self.get_serializer_for(klass)
       end
     end
 
-    attr_accessor :object, :root, :scope
+    attr_accessor :object, :root, :scope, :links
     class_attribute :_type, instance_writer: false
+    class_attribute :_links_block, instance_writer: false
 
     def initialize(object, options = {})
       self.object = object
@@ -136,6 +141,13 @@ def initialize(object, options = {})
           define_method scope_name, lambda { scope }
         end
       end
+
+      instance_eval(&_links_block) if _links_block
+    end
+
+    def link(name, value)
+      self.links ||= {}
+      self.links[name] = value
     end
 
     def json_key
diff --git a/lib/active_model/serializer/adapter/json_api.rb b/lib/active_model/serializer/adapter/json_api.rb
index 2792af094..9b29ed957 100644
--- a/lib/active_model/serializer/adapter/json_api.rb
+++ b/lib/active_model/serializer/adapter/json_api.rb
@@ -93,7 +93,7 @@ def serializable_hash_for_collection(options)
 
           if serializer.paginated?
             hash[:links] ||= {}
-            hash[:links].update(links_for(serializer, options))
+            hash[:links].update(pagination_links_for(serializer, options))
           end
 
           hash
@@ -134,13 +134,24 @@ def resource_identifier_for(serializer)
           { id: id.to_s, type: type }
         end
 
+        def attributes_for(serializer, fields)
+          attributes = serializer.attributes.except(:id)
+          attributes.slice!(*fields) if fields
+
+          attributes
+        end
+
         def resource_object_for(serializer)
           cache_check(serializer) do
             resource_object = resource_identifier_for(serializer)
+
             requested_fields = fieldset && fieldset.fields_for(resource_object[:type])
-            attributes = serializer.attributes.except(:id)
-            attributes.slice!(*requested_fields) if requested_fields
+            attributes = attributes_for(serializer, requested_fields)
             resource_object[:attributes] = attributes if attributes.any?
+
+            links = links_for(serializer)
+            resource_object[:links] = links if links.any?
+
             resource_object
           end
         end
@@ -200,7 +211,11 @@ def add_included_resources_for(serializer, include_tree, included)
           end
         end
 
-        def links_for(serializer, options)
+        def links_for(serializer)
+          serializer.links || {}
+        end
+
+        def pagination_links_for(serializer, options)
           JsonApi::PaginationLinks.new(serializer.object, options[:context]).serializable_hash(options)
         end
       end
diff --git a/test/adapter/json_api/links_test.rb b/test/adapter/json_api/links_test.rb
new file mode 100644
index 000000000..7c79e5d31
--- /dev/null
+++ b/test/adapter/json_api/links_test.rb
@@ -0,0 +1,37 @@
+require 'test_helper'
+
+LinkPost = Class.new(Model)
+class LinkPostSerializer < ActiveModel::Serializer
+  belongs_to :link_author
+end
+
+LinkAuthor = Class.new(Model)
+class LinkAuthorSerializer < ActiveModel::Serializer
+  links do
+    link :self, href: "//example.com/link_author/#{object.id}"
+  end
+end
+
+module ActiveModel
+  class Serializer
+    module Adapter
+      class JsonApi
+        class LinksTest < Minitest::Test
+          def setup
+            @author = LinkAuthor.new(id: 1337)
+          end
+
+          def test_resource_links
+            hash = serializable(@author, adapter: :json_api).serializable_hash
+            expected = {
+              self: {
+                href: '//example.com/link_author/1337'
+              }
+            }
+            assert_equal(expected, hash[:data][:links])
+          end
+        end
+      end
+    end
+  end
+end