allow conditional relationships

lib/fast_jsonapi/object_serializer.rb

@@ -221,7 +221,8 @@ module FastJsonapi
           serializer: compute_serializer_name(options[:serializer] || base_key_sym),
           relationship_type: relationship_type,
           cached: options[:cached] || false,
-          polymorphic: fetch_polymorphic_option(options)
+          polymorphic: fetch_polymorphic_option(options),
+          conditional_proc: options[:if]
         }
       end
 

lib/fast_jsonapi/serialization_core.rb

@@ -82,6 +82,8 @@ module FastJsonapi
         relationships = relationships_to_serialize if relationships.nil?
 
         relationships.each_with_object({}) do |(_k, relationship), hash|
+          conditional_proc = relationship[:conditional_proc]
+          if conditional_proc.blank? || conditional_proc.call(record, params)
             name = relationship[:key]
             empty_case = relationship[:relationship_type] == :has_many ? [] : nil
             hash[name] = {
@@ -89,6 +91,7 @@ module FastJsonapi
             }
           end
         end
+      end
 
       def record_hash(record, params = {})
         if cached

spec/lib/object_serializer_spec.rb

@@ -341,4 +341,33 @@ describe FastJsonapi::ObjectSerializer do
       expect(serializable_hash['data']['attributes'].has_key?('director')).to be_falsey
     end
   end
+
+  context 'when optional relationships are determined by record data' do
+    it 'returns optional relationship when relationship is included' do
+      json = MovieOptionalRelationshipSerializer.new(movie).serialized_json
+      serializable_hash = JSON.parse(json)
+      expect(serializable_hash['data']['relationships'].has_key?('actors')).to be_truthy
+    end
+
+    it "doesn't return optional relationship when relationship is not included" do
+      movie.actor_ids = []
+      json = MovieOptionalRelationshipSerializer.new(movie).serialized_json
+      serializable_hash = JSON.parse(json)
+      expect(serializable_hash['data']['relationships'].has_key?('actors')).to be_falsey
+    end
+  end
+
+  context 'when optional relationships are determined by params data' do
+    it 'returns optional relationship when relationship is included' do
+      json = MovieOptionalRelationshipWithParamsSerializer.new(movie, { params: { admin: true }}).serialized_json
+      serializable_hash = JSON.parse(json)
+      expect(serializable_hash['data']['relationships'].has_key?('actors')).to be_truthy
+    end
+
+    it "doesn't return optional relationship when relationship is not included" do
+      json = MovieOptionalRelationshipWithParamsSerializer.new(movie, { params: { admin: false }}).serialized_json
+      serializable_hash = JSON.parse(json)
+      expect(serializable_hash['data']['relationships'].has_key?('actors')).to be_falsey
+    end
+  end
 end

spec/shared/contexts/movie_context.rb

@@ -292,6 +292,20 @@ RSpec.shared_context 'movie class' do
       attributes :name
       attribute :director, if: Proc.new { |record, params| params && params[:admin] == true }
     end
+
+    class MovieOptionalRelationshipSerializer
+      include FastJsonapi::ObjectSerializer
+      set_type :movie
+      attributes :name
+      has_many :actors, if: Proc.new { |record| record.actors.any? }
+    end
+
+    class MovieOptionalRelationshipWithParamsSerializer
+      include FastJsonapi::ObjectSerializer
+      set_type :movie
+      attributes :name
+      has_many :actors, if: Proc.new { |record, params| params && params[:admin] == true }
+    end
   end