Add test for Issue JSONAPI-Resources#1473: Polymorphic has_many relationships

Issue JSONAPI-Resources#1473 reported problems with polymorphic has_many relationships
in v0-11-dev branch. This test verifies that the current master branch
handles these relationships correctly.

Test scenario:
- Article has_many :article_comments, as: :commentable
- ArticleComment belongs_to :commentable, polymorphic: true
- ArticleResource has_many :article_comments, foreign_key_on: :related

The test confirms that including polymorphic has_many relationships
works without attempting invalid inverse joins.

Note: This issue appears to be specific to v0-11-dev branch and does
not affect the current master branch.

Related: https://github.com/cerebris/jsonapi-resources/issues/1473

Author: takaokouji

test/controllers/articles_controller_test.rb

@@ -0,0 +1,43 @@
+require File.expand_path('../../test_helper', __FILE__)
+
+# Test for Issue #1473: Inverse polymorphic relationship error
+# https://github.com/cerebris/jsonapi-resources/issues/1473
+
+class ArticlesControllerTest < ActionController::TestCase
+  def setup
+    DatabaseCleaner.start
+    JSONAPI.configuration.json_key_format = :underscored_key
+    @article = Article.create!(title: 'Test Article')
+    @comment1 = ArticleComment.create!(
+      content: 'First comment',
+      commentable: @article
+    )
+    @comment2 = ArticleComment.create!(
+      content: 'Second comment',
+      commentable: @article
+    )
+  end
+
+  def teardown
+    DatabaseCleaner.clean
+  end
+
+  # Test that including polymorphic has_many relationships works
+  # Issue #1473 reported that this would fail with:
+  # "Can't join 'ArticleComment' to association named 'article'"
+  def test_index_with_polymorphic_has_many_include
+    get :index, params: { include: 'article_comments' }
+    assert_response :success
+    assert_equal 1, json_response['data'].size
+    assert json_response['included'], "Should have included resources"
+    assert_equal 2, json_response['included'].size, "Should include 2 comments"
+  end
+
+  def test_show_with_polymorphic_has_many_include
+    get :show, params: { id: @article.id, include: 'article_comments' }
+    assert_response :success
+    assert_equal @article.id.to_s, json_response['data']['id']
+    assert json_response['included'], "Should have included resources"
+    assert_equal 2, json_response['included'].size, "Should include 2 comments"
+  end
+end

test/fixtures/active_record.rb

@@ -429,6 +429,18 @@
     t.integer :version
     t.timestamps null: false
   end
+
+  # Tables for testing Issue #1473: Polymorphic has_many with foreign_key_on: :related
+  create_table :articles, force: true do |t|
+    t.string :title
+    t.timestamps null: false
+  end
+
+  create_table :article_comments, force: true do |t|
+    t.text :content
+    t.references :commentable, polymorphic: true, index: true
+    t.timestamps null: false
+  end
 end
 
 ### MODELS
@@ -868,6 +880,15 @@ class ListItem < ActiveRecord::Base
   belongs_to :list, inverse_of: :items
 end
 
+# Models for testing Issue #1473: Polymorphic has_many with foreign_key_on: :related
+class Article < ActiveRecord::Base
+  has_many :article_comments, as: :commentable
+end
+
+class ArticleComment < ActiveRecord::Base
+  belongs_to :commentable, polymorphic: true
+end
+
 ### CONTROLLERS
 class SessionsController < ActionController::Base
   include JSONAPI::ActsAsResourceController
@@ -1230,6 +1251,13 @@ class IndicatorsController < JSONAPI::ResourceController
 class RobotsController < JSONAPI::ResourceController
 end
 
+# Controllers for testing Issue #1473
+class ArticlesController < JSONAPI::ResourceController
+end
+
+class ArticleCommentsController < JSONAPI::ResourceController
+end
+
 ### RESOURCES
 class BaseResource < JSONAPI::Resource
   abstract
@@ -2691,6 +2719,17 @@ class RobotResource < ::JSONAPI::Resource
   end
 end
 
+# Resources for testing Issue #1473: Polymorphic has_many with foreign_key_on: :related
+class ArticleResource < JSONAPI::Resource
+  attribute :title
+  has_many :article_comments, foreign_key_on: :related
+end
+
+class ArticleCommentResource < JSONAPI::Resource
+  attribute :content
+  has_one :commentable, polymorphic: true
+end
+
 ### PORO Data - don't do this in a production app
 $breed_data = BreedData.new
 $breed_data.add(Breed.new(0, 'persian'))

test/test_helper.rb

@@ -340,6 +340,10 @@ class CatResource < JSONAPI::Resource
   jsonapi_resources :employees
   jsonapi_resources :robots
 
+  # Routes for testing Issue #1473
+  jsonapi_resources :articles
+  jsonapi_resources :article_comments
+
   jsonapi_resources :lists
   jsonapi_resources :list_items
 

test/unit/resource/polymorphic_has_many_test.rb

@@ -0,0 +1,103 @@
+require File.expand_path('../../../test_helper', __FILE__)
+
+# Test for Issue #1473: Inverse polymorphic relationship error
+# https://github.com/cerebris/jsonapi-resources/issues/1473
+#
+# This test reproduces the scenario where:
+# - Article has_many :article_comments, as: :commentable
+# - ArticleComment belongs_to :commentable, polymorphic: true
+# - ArticleResource has_many :article_comments, foreign_key_on: :related
+# - Requesting articles?include=article_comments should work without
+#   attempting to use inverse joins like ArticleComment.joins(:article)
+
+class PolymorphicHasManyTest < ActiveSupport::TestCase
+  def setup
+    DatabaseCleaner.start
+    # Create test data
+    @article = Article.create!(title: 'Test Article')
+    @comment1 = ArticleComment.create!(
+      content: 'First comment',
+      commentable: @article
+    )
+    @comment2 = ArticleComment.create!(
+      content: 'Second comment',
+      commentable: @article
+    )
+  end
+
+  def teardown
+    DatabaseCleaner.clean
+  end
+
+  def test_polymorphic_has_many_find_fragments_with_include
+    # This test verifies that we can include polymorphic has_many relationships
+    # with foreign_key_on: :related without attempting invalid inverse joins
+
+    resource_klass = ArticleResource
+    context = {}
+
+    # Create include directives for article_comments
+    include_directives = JSONAPI::IncludeDirective.new(
+      resource_klass,
+      ['article_comments'],
+      allow_remote_includes: false
+    )
+
+    # Find fragments should not raise an error about missing inverse relationship
+    assert_nothing_raised do
+      fragments = resource_klass.find_fragments(
+        {},
+        {
+          context: context,
+          include_directives: include_directives
+        }
+      )
+
+      assert fragments.any?, "Should find article fragments"
+    end
+  end
+
+  def test_polymorphic_has_many_resource_set_populate
+    # Test that populating a resource set with polymorphic includes works correctly
+
+    resource_klass = ArticleResource
+    context = {}
+
+    # Find the article fragments
+    fragments = resource_klass.find_fragments({}, { context: context })
+    assert fragments.any?, "Should find article fragments"
+
+    # Create include directives
+    include_directives = JSONAPI::IncludeDirective.new(
+      resource_klass,
+      ['article_comments'],
+      allow_remote_includes: false
+    )
+
+    # Create and populate resource set
+    resource_set = JSONAPI::ResourceSet.new(resource_klass)
+    fragments.each do |fragment|
+      resource_set.add_resource_fragment(fragment, include_directives)
+    end
+
+    # This should not raise "Can't join 'ArticleComment' to association named 'article'"
+    assert_nothing_raised do
+      resource_set.populate!(context)
+    end
+
+    # Verify that the article_comments are included
+    primary_resources = resource_set.resource_set_by_resource_klass_and_id
+    assert primary_resources[resource_klass].any?, "Should have article resources"
+  end
+
+  def test_polymorphic_has_many_records_includes_work
+    # Test that the underlying ActiveRecord includes work correctly
+
+    # This should use Article.includes(:article_comments), not ArticleComment.joins(:article)
+    assert_nothing_raised do
+      articles = Article.includes(:article_comments).to_a
+      assert_equal 1, articles.size
+      assert_equal 2, articles.first.article_comments.size
+    end
+  end
+end