Allow allocated Active Records to lookup associations

Previously, the association cache isn't setup on allocated record objects,
so association lookups will crash. Test frameworks like mocha use allocate
to check for stubbable instance methods, which can trigger an association lookup.

Author: gmcgibbon

activerecord/CHANGELOG.md

@@ -1,3 +1,11 @@
+*   Allow allocated Active Records to lookup associations.
+
+    Previously, the association cache isn't setup on allocated record objects, so association
+    lookups will crash. Test frameworks like mocha use allocate to check for stubbable instance
+    methods, which can trigger an association lookup.
+
+    *Gannon McGibbon*
+
 *   Encryption now supports `support_unencrypted_data: true` being set per-attribute.
 
     Previously this only worked if `ActiveRecord::Encryption.config.support_unencrypted_data == true`.

activerecord/lib/active_record/associations.rb

@@ -79,7 +79,7 @@ def init_internals
 
       # Returns the specified association instance if it exists, +nil+ otherwise.
       def association_instance_get(name)
-        @association_cache[name]
+        (@association_cache ||= {})[name]
       end
 
       # Set the specified association instance.

activerecord/test/cases/associations_test.rb

@@ -59,6 +59,10 @@ def test_eager_loading_should_not_change_count_of_children
     assert_equal 1, liquids[0].molecules.length
   end
 
+  def test_allocated_record_can_see_assocations
+    assert_not_nil Ship.allocate.association(:parts)
+  end
+
   def test_subselect
     author = authors :david
     favs = author.author_favorites