Explicitly set serializer for associations

Document specifying serializer for assocaition

test/adapter/json_api/has_many_explicit_serializer_test.rb

@@ -0,0 +1,65 @@
+require 'test_helper'
+
+module ActiveModel
+  class Serializer
+    class Adapter
+      class JsonApi
+        # Test 'has_many :assocs, serializer: AssocXSerializer'
+        class HasManyExplicitSerializerTest < Minitest::Test
+          def setup
+            @post = Post.new(title: 'New Post', body: 'Body')
+            @author = Author.new(name: 'Jane Blogger')
+            @author.posts = [@post]
+            @post.author = @author
+            @first_comment = Comment.new(id: 1, body: 'ZOMG A COMMENT')
+            @second_comment = Comment.new(id: 2, body: 'ZOMG ANOTHER COMMENT')
+            @post.comments = [@first_comment, @second_comment]
+            @first_comment.post = @post
+            @first_comment.author = nil
+            @second_comment.post = @post
+            @second_comment.author = nil
+
+            @serializer = PostPreviewSerializer.new(@post)
+            @adapter = ActiveModel::Serializer::Adapter::JsonApi.new(
+              @serializer,
+              include: 'comments,author'
+            )
+          end
+
+          def test_includes_comment_ids
+            assert_equal(['1', '2'],
+                         @adapter.serializable_hash[:posts][:links][:comments])
+          end
+
+          def test_includes_linked_comments
+            assert_equal([{ id: '1', body: "ZOMG A COMMENT", links: { post: @post.id.to_s, author: nil }},
+                          { id: '2', body: "ZOMG ANOTHER COMMENT", links: { post: @post.id.to_s, author: nil }}],
+                         @adapter.serializable_hash[:linked][:comments])
+          end
+
+          def test_includes_author_id
+            assert_equal(@author.id.to_s,
+                         @adapter.serializable_hash[:posts][:links][:author])
+          end
+
+          def test_includes_linked_authors
+            assert_equal([{ id: @author.id.to_s, links: { posts: [@post.id.to_s] } }],
+                         @adapter.serializable_hash[:linked][:authors])
+          end
+
+          def test_explicit_serializer_with_null_resource
+            @post.author = nil
+            assert_equal(nil,
+                         @adapter.serializable_hash[:posts][:links][:author])
+          end
+
+          def test_explicit_serializer_with_null_collection
+            @post.comments = []
+            assert_equal([],
+                         @adapter.serializable_hash[:posts][:links][:comments])
+          end
+        end
+      end
+    end
+  end
+end