Fix single rel caching issue (#1713)

lib/active_graph/node/has_n.rb

@@ -111,13 +111,17 @@ def init_cache
 
       def add_to_cache(object, rel = nil)
         (@cached_rels ||= []) << rel if rel
-        (@cached_result ||= []).tap { |results| results << object if object && !results.include?(object) }
+        (@cached_result ||= []).tap { |results| results << object if !results.include?(object) } if object
       end
 
       def rels
         @cached_rels || super.tap { |rels| rels.each { |rel| add_to_cache(nil, rel)  } }
       end
 
+      def rel
+        rels.first
+      end
+
       def cache_query_proxy_result
         (result_cache_proc_cache || @query_proxy).to_a.tap { |result| cache_result(result) }
       end

spec/e2e/association_proxy_spec.rb

@@ -12,12 +12,13 @@
         has_one :out, :favorite_lesson, type: nil, model_class: :Lesson
         has_many :out, :homework, type: :HOMEWORK, model_class: %w[Lesson Exam]
         has_many :out, :friends, type: :friend, model_class: :Student
+        has_one :out, :school, rel_class: :SchoolRel
       end
 
       stub_relationship_class('LessonEnrollment') do
         from_class :Student
         to_class :Lesson
-        type :has_studet
+        type :has_student
 
         property :grade
       end
@@ -34,6 +35,17 @@
         has_many :in, :lessons, model_class: :Lesson, origin: :exams_given
         has_many :out, :students, type: :has_student, model_class: :Student
       end
+
+      stub_relationship_class('SchoolRel') do
+        from_class :Student
+        to_class :School
+        type :school
+      end
+
+      stub_node_class('School') do
+        property :name
+        has_many :out, :students, type: :school, model_class: :School
+      end
     end
 
     let(:billy) { Student.create(name: 'Billy') }
@@ -44,6 +56,7 @@
     let(:science_exam2) { Exam.create(name: 'Science Exam 2') }
     let(:leszek) { Student.create(name: 'Leszek', friends: [zinto]) }
     let(:zinto) { Student.create(name: 'Zinto') }
+    let(:code_academy) { School.create(name: 'Code Academy') }
 
     before do
       [math, science].each { |lesson| billy.lessons << lesson }
@@ -52,6 +65,7 @@
       science.exams_given << science_exam
       science.exams_given << science_exam2
       billy.favorite_lesson = math
+      billy.school = code_academy
     end
 
     context 'self referencing relationships' do
@@ -313,11 +327,17 @@
     end
 
     describe '#rels' do
-      it 'caches results for consecutive calls' do
+      it 'caches multi rels for consecutive calls' do
         expect_queries(1) do
           2.times { billy.lessons.rels }
         end
       end
+
+      it 'caches single rel for consecutive calls' do
+        expect_queries(1) do
+          2.times { billy.school(chainable: true).rel }
+        end
+      end
     end
 
     describe '#inspect' do