Allow prefetch_associations on association that was prefetched before

lib/identity_cache/cached/belongs_to.rb

@@ -77,16 +77,20 @@ def fetch_async(load_strategy, records)
             end
           end
 
-          load_strategy.load_multi(
-            reflection.klass.cached_primary_index,
-            ids_to_owner_record.keys
-          ) do |associated_records_by_id|
-            associated_records_by_id.each do |id, associated_record|
-              owner_record = ids_to_owner_record.fetch(id)
-              write(owner_record, associated_record)
-            end
+          if ids_to_owner_record.keys.any?
+            load_strategy.load_multi(
+              reflection.klass.cached_primary_index,
+              ids_to_owner_record.keys
+            ) do |associated_records_by_id|
+              associated_records_by_id.each do |id, associated_record|
+                owner_record = ids_to_owner_record.fetch(id)
+                write(owner_record, associated_record)
+              end
 
-            yield associated_records_by_id.values.compact
+              yield associated_records_by_id.values.compact
+            end
+          else
+            yield records.filter_map { |record| record.instance_variable_get(records_variable_name) }
           end
         end
       end

test/prefetch_associations_test.rb

@@ -270,6 +270,39 @@ def test_fetch_multi_batch_fetches_first_level_associations_who_dont_include_ide
       end
     end
 
+    def test_fetch_multi_batch_fetches_non_embedded_second_level_belongs_to_associations_in_repeating_prefetch
+      Item.send(:cache_belongs_to, :item)
+      AssociatedRecord.send(:cache_belongs_to, :item)
+
+      @bob_child  = @bob.associated_records.create!(name: "bob child")
+      @fred_child = @fred.associated_records.create!(name: "fred child")
+      @bob.update_attribute(:item_id, @bob.id)
+      @fred.update_attribute(:item_id, @fred.id)
+
+      # populate the cache entries and associated children ID variables
+      AssociatedRecord.fetch_multi(@bob_child.id, @fred_child.id)
+      Item.fetch_multi(@bob.id, @fred.id)
+
+      assert_memcache_operations(2) do
+        @cached_bob_child, @cached_fred_child = AssociatedRecord.fetch_multi(
+          @bob_child.id, @fred_child.id, includes: [:item]
+        )
+      end
+
+      assert_memcache_operations(1) do
+        AssociatedRecord.prefetch_associations({ item: :item }, [@cached_bob_child, @cached_fred_child])
+      end
+
+      assert_queries(0) do
+        assert_memcache_operations(0) do
+          @cached_bob_parent  = @cached_bob_child.fetch_item
+          @cached_fred_parent = @cached_fred_child.fetch_item
+          assert_equal(@bob,  @cached_bob_parent.fetch_item)
+          assert_equal(@fred, @cached_fred_parent.fetch_item)
+        end
+      end
+    end
+
     def test_fetch_multi_batch_fetches_non_embedded_second_level_has_many_associations
       Item.send(:cache_has_many, :associated_records, embed: :ids)
       AssociatedRecord.send(:cache_has_many, :deeply_associated_records, embed: :ids)