array serializer uses root option for json_key if available

lib/active_model/serializer/array_serializer.rb

@@ -5,9 +5,10 @@ module ActiveModel
       include Enumerable
       delegate :each, to: :@objects
 
-      attr_reader :meta, :meta_key
+      attr_reader :root, :meta, :meta_key
 
       def initialize(objects, options = {})
+        @root = options[:root]
         @resource = objects
         @objects  = objects.map do |object|
           serializer_class = options.fetch(
@@ -26,15 +27,8 @@ module ActiveModel
       end
 
       def json_key
-        if @objects.first
+        key = root || @objects.first.try(:json_key) || @resource.try(:name).try(:underscore)
-          @objects.first.json_key.pluralize
+        key.try(:pluralize)
-        else
-          @resource.name.underscore.pluralize if @resource.try(:name)
-        end
-      end
-
-      def root=(root)
-        @objects.first.root = root if @objects.first
       end
     end
   end

test/array_serializer_test.rb

@@ -6,7 +6,13 @@ module ActiveModel
       def setup
         @comment = Comment.new
         @post = Post.new
-        @serializer = ArraySerializer.new([@comment, @post], {some: :options})
+        @resource = build_named_collection @comment, @post
+        @serializer = ArraySerializer.new(@resource, {some: :options})
+      end
+
+      def build_named_collection(*resource)
+        resource.define_singleton_method(:name){ 'MeResource' }
+        resource
       end
 
       def test_respond_to_each
@@ -39,15 +45,52 @@ module ActiveModel
         assert_equal @serializer.meta_key, "the meta key"
       end
 
-      def test_json_key_when_resource_is_empty
+      def test_root_default
-        Array.class_eval do
+        @serializer = ArraySerializer.new([@comment, @post])
-          def name
+        assert_equal @serializer.root, nil
-            'PostComment'
       end
+
+      def test_root
+        expected =  'custom_root'
+        @serializer = ArraySerializer.new([@comment, @post], root: expected)
+        assert_equal @serializer.root, expected
       end
-        @post_comments = []
+
-        @serializer = ArraySerializer.new(@post_comments)
+      def test_root_with_no_serializers
-        assert_equal @serializer.json_key, "post_comments"
+        expected =  'custom_root'
+        @serializer = ArraySerializer.new([], root: expected)
+        assert_equal @serializer.root, expected
+      end
+
+      def test_json_key
+        assert_equal @serializer.json_key, 'comments'
+      end
+
+      def test_json_key_with_resource_with_name_and_no_serializers
+        serializer = ArraySerializer.new(build_named_collection)
+        assert_equal serializer.json_key, 'me_resources'
+      end
+
+      def test_json_key_with_resource_with_nil_name_and_no_serializers
+        resource = []
+        resource.define_singleton_method(:name){ nil }
+        serializer = ArraySerializer.new(resource)
+        assert_equal serializer.json_key, nil
+      end
+
+      def test_json_key_with_resource_without_name_and_no_serializers
+        serializer = ArraySerializer.new([])
+        assert_equal serializer.json_key, nil
+      end
+
+      def test_json_key_with_root
+        serializer = ArraySerializer.new(@resource, root: 'custom_root')
+        assert_equal serializer.json_key, 'custom_roots'
+      end
+
+      def test_json_key_with_root_and_no_serializers
+        serializer = ArraySerializer.new(build_named_collection, root: 'custom_root')
+        assert_equal serializer.json_key, 'custom_roots'
       end
     end
   end