Fix nested namespaces parsing and resource resolving

(cherry picked from commit bbebf89)

Author: elvanja

lib/jsonapi/request_parser.rb

@@ -474,7 +474,7 @@ def parse_to_one_relationship(link_value, relationship)
 
       unless links_object[:id].nil?
         resource = self.resource_klass || Resource
-        relationship_resource = resource.resource_for(unformat_key(links_object[:type]).to_s)
+        relationship_resource = resource.resource_for(unformat_key(relationship.options[:class_name] || links_object[:type]).to_s)
         relationship_id = relationship_resource.verify_key(links_object[:id], @context)
         if relationship.polymorphic?
           { id: relationship_id, type: unformat_key(links_object[:type].to_s) }

lib/jsonapi/resource.rb

@@ -453,7 +453,7 @@ def rebuild_relationships(relationships)
 
       def resource_for(type)
         type = type.underscore
-        type_with_module = type.include?('/') ? type : module_path + type
+        type_with_module = type.start_with?(module_path) ? type : module_path + type
 
         resource_name = _resource_name_from_type(type_with_module)
         resource = resource_name.safe_constantize if resource_name

test/unit/resource/resource_test.rb

@@ -85,11 +85,18 @@ module MyModule
   class MyNamespacedResource < JSONAPI::Resource
     model_name "Person"
     has_many :related
+    has_one :default_profile, class_name: "Nested::Profile"
   end
 
   class RelatedResource < JSONAPI::Resource
     model_name "Comment"
   end
+
+  module Nested
+    class ProfileResource < JSONAPI::Resource
+      model_name "Nested::Profile"
+    end
+  end
 end
 
 module MyAPI
@@ -155,6 +162,12 @@ def test_resource_for_namespaced_resource
     assert_equal(MyModule::MyNamespacedResource.resource_for('related'), MyModule::RelatedResource)
   end
 
+  def test_resource_for_nested_namespaced_resource
+    assert_equal(JSONAPI::Resource.resource_for('my_module/nested/profile'), MyModule::Nested::ProfileResource)
+    assert_equal(MyModule::MyNamespacedResource.resource_for('my_module/nested/profile'), MyModule::Nested::ProfileResource)
+    assert_equal(MyModule::MyNamespacedResource.resource_for('nested/profile'), MyModule::Nested::ProfileResource)
+  end
+
   def test_relationship_parent_point_to_correct_resource
     assert_equal MyModule::MyNamespacedResource, MyModule::MyNamespacedResource._relationships[:related].parent_resource
   end