Adds tests and documentation for polymorphism

CHANGELOG.md

@@ -47,6 +47,7 @@ Misc:
 - [#1535](https://github.com/rails-api/active_model_serializers/pull/1535) Move the adapter and adapter folder to
   active_model_serializers folder and changes the module namespace. (@domitian @bf4)
 - [#1497](https://github.com/rails-api/active_model_serializers/pull/1497) Add JRuby-9000 to appveyor.yml(@corainchicago)
+- [#1420](https://github.com/rails-api/active_model_serializers/pull/1420) Adds tests and documentation for polymorphism(@marcgarreau)
 
 ### v0.10.0.rc4 (2016/01/27 11:00 +00:00)
 Breaking changes:

docs/general/serializers.md

@@ -76,6 +76,18 @@ def blog
 end
 ```
 
+### Polymorphic Relationships
+
+Polymorphic relationships are serialized by specifying the relationship, like any other association. For example:
+
+```ruby
+class PictureSerializer < ActiveModel::Serializer
+  has_one :imageable
+end
+```
+
+For more context, see the [tests](../../test/adapter/polymorphic_test.rb) for each adapter.
+
 ### Caching
 
 #### ::cache

test/adapter/polymorphic_test.rb

@@ -0,0 +1,72 @@
+require 'test_helper'
+
+module ActiveModel
+  class Serializer
+    module Adapter
+      class PolymorphicTest < ActiveSupport::TestCase
+        setup do
+          @employee = Employee.new(id: 42, name: 'Zoop Zoopler', email: 'zoop@example.com')
+          @picture = @employee.pictures.new(id: 1, title: 'headshot-1.jpg')
+          @picture.imageable = @employee
+
+          @attributes_serialization = serializable(@picture, serializer: PolymorphicBelongsToSerializer) # uses default adapter: attributes
+          @json_serialization = serializable(@picture, adapter: :json, serializer: PolymorphicBelongsToSerializer)
+          @json_api_serialization = serializable(@picture, adapter: :json_api, serializer: PolymorphicBelongsToSerializer)
+        end
+
+        def test_attributes_serialization
+          expected =
+            {
+              id: 1,
+              title: 'headshot-1.jpg',
+              imageable: {
+                id: 42,
+                name: 'Zoop Zoopler'
+              }
+            }
+
+          assert_equal(expected, @attributes_serialization.as_json)
+        end
+
+        def test_json_serializer
+          expected =
+            {
+              picture: {
+                id: 1,
+                title: 'headshot-1.jpg',
+                imageable: {
+                  id: 42,
+                  name: 'Zoop Zoopler'
+                }
+              }
+            }
+
+          assert_equal(expected, @json_serialization.as_json)
+        end
+
+        def test_json_api_serializer
+          expected =
+            {
+              data: {
+                id: '1',
+                type: 'pictures',
+                attributes: {
+                  title: 'headshot-1.jpg'
+                },
+                relationships: {
+                  imageable: {
+                    data: {
+                      id: '42',
+                      type: 'employees'
+                    }
+                  }
+                }
+              }
+            }
+
+          assert_equal(expected, @json_api_serialization.as_json)
+        end
+      end
+    end
+  end
+end

test/fixtures/active_record.rb

@@ -18,6 +18,17 @@
     t.references :post
     t.timestamp null: false
   end
+  create_table :employees, force: true do |t|
+    t.string :name
+    t.string :email
+    t.timestamp null: false
+  end
+  create_table :pictures, force: true do |t|
+    t.string :title
+    t.string :imageable_type
+    t.string :imageable_id
+    t.timestamp null: false
+  end
 end
 
 module ARModels

test/fixtures/poro.rb

@@ -72,6 +72,14 @@ def cache_key
   end
 end
 
+class Employee < ActiveRecord::Base
+  has_many :pictures, as: :imageable
+end
+
+class Picture < ActiveRecord::Base
+  belongs_to :imageable, polymorphic: true
+end
+
 module Spam; end
 Spam::UnrelatedLink = Class.new(Model)
 
@@ -233,6 +241,16 @@ def maker
   end
 end
 
+PolymorphicHasManySerializer = Class.new(ActiveModel::Serializer) do
+  attributes :id, :name
+end
+
+PolymorphicBelongsToSerializer = Class.new(ActiveModel::Serializer) do
+  attributes :id, :title
+
+  has_one :imageable, serializer: PolymorphicHasManySerializer
+end
+
 Spam::UnrelatedLinkSerializer = Class.new(ActiveModel::Serializer) do
   cache only: [:id]
   attributes :id