feat: Use the association options to lookup relationship class

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## Unreleased
 
+- [#403](https://github.com/JsonApiClient/json_api_client/pull/403) - Feature: Use the association options to lookup relationship class
 - [#406](https://github.com/JsonApiClient/json_api_client/pull/406) - Deep-merge nested `additional_params`
 
 ## 1.21.1

lib/json_api_client/utils.rb

@@ -7,6 +7,11 @@ def self.compute_type(klass, type_name)
       # the type_name is an absolute reference.
       return type_name.constantize if type_name.match(/^::/)
 
+      # Check the klass association definitions
+      association_klass_match = klass.associations.find { |a| a.attr_name.to_s.singularize == type_name.underscore }
+      association_klass = association_klass_match.options[:class] if association_klass_match
+      return association_klass if association_klass
+
       # Build a list of candidates to search for
       candidates = []
       klass.name.scan(/::|$/) { candidates.unshift "#{$`}::#{type_name}" }

test/unit/association_test.rb

@@ -89,8 +89,21 @@ class Employee < TestResource
   has_one :chief, klass: 'Employee'
 end
 
-class AssociationTest < Minitest::Test
+module CrossNamespaceTwo
+  class Nail < TestResource
+    property :size
+  end
+end
+
+module CrossNamespaceOne
+  class Hammer < TestResource
+    property :brand
 
+    has_many :nails, class: CrossNamespaceTwo::Nail
+  end
+end
+
+class AssociationTest < Minitest::Test
   def test_default_properties_no_changes
     stub_request(:post, 'http://example.com/accounts').
         with(headers: { content_type: 'application/vnd.api+json', accept: 'application/vnd.api+json' }, body: {
@@ -1070,4 +1083,62 @@ def test_does_not_load_include_from_dataset
     assert_nil(records.first.chief)
   end
 
+  def test_cross_namespace_resource_references
+    stub_request(:get, 'http://example.com/hammers?include=nails')
+        .to_return(
+            headers: {
+                content_type: 'application/vnd.api+json'
+            }, body: {
+            data: [
+                {
+                  id: '1',
+                  type: 'hammers',
+                  attributes: {
+                      brand: 'Hardware Store'
+                  },
+                  relationships: {
+                    nails: { data: [{id: '2', type: 'nails'}] }
+                  }
+                },
+                {
+                  id: '2',
+                  type: 'hammers',
+                  attributes: {
+                      brand: 'Hardware Store'
+                  },
+                  relationships: {
+                    nails: { data: [{id: '3', type: 'nails'}] }
+                  }
+                }
+            ],
+            included: [
+                {
+                  id: '2',
+                  type: 'nails',
+                  attributes: {
+                      size: 10
+                  }
+                },
+                {
+                  id: '3',
+                  type: 'nails',
+                  attributes: {
+                      size: 8
+                  }
+              }
+            ]
+        }.to_json)
+
+    records = CrossNamespaceOne::Hammer.includes(:nails).to_a
+
+    assert_equal(2, records.size)
+    assert_equal('1', records.first.id)
+    assert_equal('2', records.second.id)
+    assert_equal('2', records.first.nails.first.id)
+    assert_equal('3', records.second.nails.first.id)
+
+    assert_equal(1, records.first.nails.size)
+    assert_equal(1, records.second.nails.size)
+  end
+
 end