Allow fieldsets to specify no attributes/relationships

lib/fast_jsonapi/serialization_core.rb

@@ -44,6 +44,8 @@ module FastJsonapi
       def attributes_hash(record, fieldset = nil, params = {})
         attributes = attributes_to_serialize
         attributes = attributes.slice(*fieldset) if fieldset.present?
+        attributes = {} if fieldset == []
+
         attributes.each_with_object({}) do |(_k, attribute), hash|
           attribute.serialize(record, params, hash)
         end
@@ -52,6 +54,7 @@ module FastJsonapi
       def relationships_hash(record, relationships = nil, fieldset = nil, params = {})
         relationships = relationships_to_serialize if relationships.nil?
         relationships = relationships.slice(*fieldset) if fieldset.present?
+        relationships = {} if fieldset == []
 
         relationships.each_with_object({}) do |(_k, relationship), hash|
           relationship.serialize(record, params, hash)

spec/lib/object_serializer_fields_spec.rb

@@ -22,6 +22,18 @@ describe FastJsonapi::ObjectSerializer do
     expect(hash[:data][:relationships].keys.sort).to eq %i[actors advertising_campaign]
   end
 
+  it 'returns no fields when none are specified' do
+    hash = MovieSerializer.new(movie, fields: { movie: [] }).serializable_hash
+
+    expect(hash[:data][:attributes].keys).to eq []
+  end
+
+  it 'returns no relationships when none are specified' do
+    hash = MovieSerializer.new(movie, fields: { movie: [] }).serializable_hash
+
+    expect(hash[:data][:relationships].keys).to eq []
+  end
+
   it 'only returns specified fields for included relationships' do
     hash = MovieSerializer.new(movie, fields: fields, include: %i[actors]).serializable_hash
 
@@ -45,4 +57,25 @@ describe FastJsonapi::ObjectSerializer do
 
     expect(hash[:included][3][:relationships].keys.sort).to eq %i[movie]
   end
+
+  context 'with no included fields specified' do
+    let(:fields) do
+      {
+        movie: %i[name actors advertising_campaign],
+        actor: []
+      }
+    end
+
+    it 'returns no fields for included relationships when none are specified' do
+      hash = MovieSerializer.new(movie, fields: fields, include: %i[actors advertising_campaign]).serializable_hash
+
+      expect(hash[:included][2][:attributes].keys).to eq []
+    end
+
+    it 'returns no relationships when none are specified' do
+      hash = MovieSerializer.new(movie, fields: fields, include: %i[actors advertising_campaign]).serializable_hash
+
+      expect(hash[:included][2][:relationships].keys).to eq []
+    end
+  end
 end