Introduce the ability to add meta tag for every resource in the collection

Author: manojmj92

README.md

@@ -245,6 +245,23 @@ class MovieSerializer
 end
 ```
 
+### Meta Per Resource
+
+For every resource in the collection, you can include a meta object containing non-standard meta-information about a resource that can not be represented as an attribute or relationship.
+
+
+```ruby
+class MovieSerializer
+  include FastJsonapi::ObjectSerializer
+
+  meta do |movie|
+    {
+      years_since_release: Date.current.year - movie.year
+    }
+  end
+end
+```
+
 ### Compound Document
 
 Support for top-level and nested included associations through ` options[:include] `.

lib/fast_jsonapi/object_serializer.rb

@@ -120,6 +120,7 @@ def inherited(subclass)
         subclass.data_links = data_links
         subclass.cached = cached
         subclass.set_type(subclass.reflected_record_type) if subclass.reflected_record_type
+        subclass.meta_to_serialize = meta_to_serialize
       end
 
       def reflected_record_type
@@ -218,6 +219,10 @@ def belongs_to(relationship_name, options = {}, &block)
         add_relationship(relationship)
       end
 
+      def meta(&block)
+        self.meta_to_serialize = block
+      end
+
       def create_relationship(base_key, relationship_type, options, block)
         name = base_key.to_sym
         if relationship_type == :has_many

lib/fast_jsonapi/serialization_core.rb

@@ -21,7 +21,8 @@ class << self
                       :cache_length,
                       :race_condition_ttl,
                       :cached,
-                      :data_links
+                      :data_links,
+                      :meta_to_serialize
       end
     end
 
@@ -57,6 +58,10 @@ def relationships_hash(record, relationships = nil, fieldset = nil, params = {})
         end
       end
 
+      def meta_hash(record, params = {})
+        meta_to_serialize.call(record, params)
+      end
+
       def record_hash(record, fieldset, params = {})
         if cached
           record_hash = Rails.cache.fetch(record.cache_key, expires_in: cache_length, race_condition_ttl: race_condition_ttl) do
@@ -68,12 +73,14 @@ def record_hash(record, fieldset, params = {})
             temp_hash
           end
           record_hash[:relationships] = record_hash[:relationships].merge(relationships_hash(record, uncachable_relationships_to_serialize, params)) if uncachable_relationships_to_serialize.present?
+          record_hash[:meta] = meta_hash(record, params) if meta_to_serialize.present?
           record_hash
         else
           record_hash = id_hash(id_from_record(record), record_type, true)
           record_hash[:attributes] = attributes_hash(record, fieldset, params) if attributes_to_serialize.present?
           record_hash[:relationships] = relationships_hash(record, nil, fieldset, params) if relationships_to_serialize.present?
           record_hash[:links] = links_hash(record, params) if data_links.present?
+          record_hash[:meta] = meta_hash(record, params) if meta_to_serialize.present?
           record_hash
         end
       end

spec/lib/object_serializer_class_methods_spec.rb

@@ -249,6 +249,34 @@
     end
   end
 
+  describe '#meta' do
+    subject(:serializable_hash) { MovieSerializer.new(movie).serializable_hash }
+
+    before do
+      movie.release_year = 2008
+      MovieSerializer.meta do |movie|
+        {
+          years_since_release: year_since_release_calculator(movie.release_year)
+        }
+      end
+    end
+
+    after do
+      movie.release_year = nil
+      MovieSerializer.meta_to_serialize = nil
+    end
+
+    it 'returns correct hash when serializable_hash is called' do
+      expect(serializable_hash[:data][:meta]).to eq ({ years_since_release: year_since_release_calculator(movie.release_year) })
+    end
+
+    private
+
+    def year_since_release_calculator(release_year)
+      Date.current.year - release_year
+    end
+  end
+
   describe '#link' do
     subject(:serializable_hash) { MovieSerializer.new(movie).serializable_hash }