Initialize class_name for a relationship from the model by default.

Author: lgebhardt

lib/jsonapi/resource.rb

@@ -673,6 +673,13 @@ def _add_relationship(klass, *attrs)
 
         attrs.each do |attr|
           check_reserved_relationship_name(attr)
+
+          # Initialize from the model's properties.
+          model_association = _model_class.reflect_on_association(attr)
+          if model_association
+            options[:class_name] ||= model_association.class_name
+          end
+
           @_relationships[attr] = relationship = klass.new(attr, options)
 
           associated_records_method_name = case relationship

test/fixtures/active_record.rb

@@ -254,6 +254,21 @@ class Tag < ActiveRecord::Base
 class Section < ActiveRecord::Base
 end
 
+class HairCut < ActiveRecord::Base
+end
+
+class Property < ActiveRecord::Base
+end
+
+class Customer < ActiveRecord::Base
+end
+
+class BadlyNamedAttributes < ActiveRecord::Base
+end
+
+class Cat < ActiveRecord::Base
+end
+
 class IsoCurrency < ActiveRecord::Base
   self.primary_key = :code
   # has_many :expense_entries, foreign_key: 'currency_code'
@@ -896,8 +911,8 @@ def self.verify_key(key, context = nil)
 class PreferencesResource < JSONAPI::Resource
   attribute :advanced_mode
 
-  has_one :author, foreign_key: :person_id, class_name: 'Person'
-  has_many :friends, class_name: 'Person'
+  has_one :author, foreign_key: :person_id
+  has_many :friends
 
   def self.find_by_key(key, options = {})
     new(Preferences.first)
@@ -961,7 +976,7 @@ class PostResource < JSONAPI::Resource
       attribute :body
       attribute :subject
 
-      has_one :writer, foreign_key: 'author_id'
+      has_one :writer, foreign_key: 'author_id', class_name: 'Writer'
       has_one :section
       has_many :comments, acts_as_set: false