Singularize and capitalize polymorphic types for presence validation

Singularizing polymorphic association types allows you to use plural or singular
type values in your requests as allowed by JSON API.

Because ActiveRecord calls #constantize on the polymorphic association type
when you use the hash to create a new model if you validate the presence of
the related model, you must capitalize the type to avoid a NameError.

Author: dpdawson

CHANGELOG.md

@@ -26,6 +26,10 @@ Features:
 - [#1340](https://github.com/rails-api/active_model_serializers/pull/1340) Add support for resource-level meta. (@beauby)
 
 Fixes:
+- [#1615](https://github.com/rails-api/active_model_serializers/pull/1615) Allow plural polymorphic relationship types when validating
+  presence. (@dpdawson)
+- [#1615](https://github.com/rails-api/active_model_serializers/pull/1615) Capitalize polymorphic association types to prevent error
+  when ActiveRecord constantizes them when validating presence. (@dpdawson)
 - [#1478](https://github.com/rails-api/active_model_serializers/pull/1478) Cache store will now be correctly set when serializers are
   loaded *before* Rails initializes. (@bf4)
 - [#1570](https://github.com/rails-api/active_model_serializers/pull/1570) Fixed pagination issue with last page size. (@bmorrall)

docs/general/deserialization.md

@@ -91,7 +91,7 @@ ActiveModelSerializers::Deserialization
 #   title: 'Title 1',
 #   published_at: '2015-12-20',
 #   author_id: '2',
-#   author_type: 'user'
+#   author_type: 'User'
 # }
 ```
 

lib/active_model_serializers/adapter/json_api/deserialization.rb

@@ -69,7 +69,7 @@ module Deserialization
         #     #   title: 'Title 1',
         #     #   published_at: '2015-12-20',
         #     #   author_id: '2',
-        #     #   author_type: 'people'
+        #     #   author_type: 'People'
         #     # }
         #
         def parse!(document, options = {})
@@ -188,7 +188,7 @@ def parse_relationship(assoc_name, assoc_data, options)
             end
 
           polymorphic = (options[:polymorphic] || []).include?(assoc_name.to_sym)
-          hash["#{prefix_key}_type".to_sym] = assoc_data['type'] if polymorphic
+          hash["#{prefix_key}_type".to_sym] = assoc_data['type'].singularize.capitalize if polymorphic
 
           hash
         end

test/active_record_test.rb

@@ -5,5 +5,38 @@ class ActiveRecordTest < ActiveSupport::TestCase
 
   def setup
     @resource = ARModels::Post.new
+    @image = Image.create
+  end
+
+  def test_active_model_record_with_validated_polymorphic_relationship_creation
+    picture = Picture.create!(picture_params)
+
+    assert_equal(@image, picture.imageable)
+  end
+
+  private
+
+  def picture_params
+    params = ActionController::Parameters.new({
+      data: {
+        attributes: {
+          title: 'Picture Title'
+        },
+        relationships: {
+          imageable: {
+            data: {
+              type: 'images',
+              id: @image.id
+            }
+          },
+        },
+        type: 'pictures'
+      }
+    })
+
+    ActiveModelSerializers::Deserialization.jsonapi_parse!(
+      params.to_unsafe_h,
+      polymorphic: [:imageable]
+    )
   end
 end

test/adapter/json_api/parse_test.rb

@@ -125,7 +125,7 @@ def test_polymorphic
               src: 'http://example.com/images/productivity.png',
               author_id: nil,
               photographer_id: '9',
-              photographer_type: 'people',
+              photographer_type: 'Person',
               comment_ids: %w(1 2)
             }
             assert_equal(expected, parsed_hash)

test/fixtures/active_record.rb

@@ -26,8 +26,10 @@
   end
   create_table :pictures, force: true do |t|
     t.string :title
-    t.string :imageable_type
-    t.string :imageable_id
+    t.references :imageable, polymorphic: true
+    t.timestamp null: false
+  end
+  create_table :images, force: true do |t|
     t.timestamp null: false
   end
 end

test/fixtures/poro.rb

@@ -78,6 +78,12 @@ class Employee < ActiveRecord::Base
 
 class Picture < ActiveRecord::Base
   belongs_to :imageable, polymorphic: true
+
+  validates :imageable, presence: true
+end
+
+class Image < ActiveRecord::Base
+  has_many :pictures, as: :imageable
 end
 
 module Spam; end