Better detection of standard preload

This ends up being an optimization.
But when preloading `[:association]`, it runs a separate preloader on `:association`.
This skips the interim step

Author: kbrock

lib/active_record/virtual_attributes/virtual_fields.rb

@@ -152,8 +152,12 @@ def call
 
           # convert the includes with virtual attributes to includes with proper associations
           records_by_assoc = records.group_by { |rec| assoc_cache[rec.class] }
-          # if these are the same includes, then do the preloader work
-          return super if records_by_assoc.size == 1 && records_by_assoc.keys.first == associations
+          # If the association were already translated, then short circuit / do the standard preloader work.
+          # When replace_virtual_fields removes the outer array, match that too.
+          if records_by_assoc.size == 1 &&
+            (associations == records_by_assoc.keys.first || associations == [records_by_assoc.keys.first])
+            return super
+          end
 
           # for each of the associations, run a preloader
           records_by_assoc.each do |klass_associations, klass_records|

spec/virtual_includes_spec.rb

@@ -180,12 +180,6 @@
       expect(Author.includes(:books => :author_name).references(:books)).to preload_values(:first_book_author_name, author_name)
       expect(Author.includes(:books => [:author_name]).references(:books)).to preload_values(:first_book_author_name, author_name)
       expect(Author.includes(:books => {:author_name => {}}).references(:books)).to preload_values(:first_book_author_name, author_name)
-    end
-
-    it "uses preloaded fields" do
-      expect(Author.includes(:books => :author_name).references(:books)).to preload_values(:first_book_author_name, author_name)
-      expect(Author.includes(:books => [:author_name]).references(:books)).to preload_values(:first_book_author_name, author_name)
-      expect(Author.includes(:books => {:author_name => {}}).references(:books)).to preload_values(:first_book_author_name, author_name)
       inc = Author.virtual_includes(:first_book_author_name)
       expect(Author.includes(inc).references(:books)).to preload_values(:first_book_author_name, author_name)
     end
@@ -308,10 +302,6 @@
     it "uses included fields" do
       expect(preloaded(Author.all.to_a, :books => :author_name)).to preload_values(:first_book_author_name, author_name)
     end
-
-    it "uses preloaded fields" do
-      expect(preloaded(Author.all.to_a, :books => :author_name)).to preload_values(:first_book_author_name, author_name)
-    end
   end
 
   context "preloads virtual_reflection with includes" do
@@ -386,11 +376,49 @@
     end
   end
 
+  describe ".eager_load" do
+    it "preloads standard associations (:books)" do
+      expect(Author.eager_load(:books)).to preload_values(:first_book_name, book_name)
+      expect(Author.eager_load([:books])).to preload_values(:first_book_name, book_name)
+      expect(Author.eager_load([[:books]])).to preload_values(:first_book_name, book_name)
+      expect(Author.eager_load(:books => {})).to preload_values(:first_book_name, book_name)
+    end
+
+    it "preloads associations (:uses => :books)" do
+      expect(Author.eager_load(:first_book_name)).to preload_values(:first_book_name, book_name)
+      expect(Author.eager_load([:first_book_name])).to preload_values(:first_book_name, book_name)
+      expect(Author.eager_load([[:first_book_name]])).to preload_values(:first_book_name, book_name)
+      expect(Author.eager_load(:first_book_name => {})).to preload_values(:first_book_name, book_name)
+    end
+  end
+
+  describe ".preload" do
+    it "preloads standard associations (:books)" do
+      expect(Author.preload(:books)).to preload_values(:first_book_name, book_name)
+      expect(Author.preload([:books])).to preload_values(:first_book_name, book_name)
+      expect(Author.preload([[:books]])).to preload_values(:first_book_name, book_name)
+      expect(Author.preload(:books => {})).to preload_values(:first_book_name, book_name)
+    end
+
+    it "preloads associations (:uses => :books)" do
+      expect(Author.preload(:first_book_name)).to preload_values(:first_book_name, book_name)
+      expect(Author.preload([:first_book_name])).to preload_values(:first_book_name, book_name)
+      expect(Author.preload([[:first_book_name]])).to preload_values(:first_book_name, book_name)
+      expect(Author.preload(:first_book_name => {})).to preload_values(:first_book_name, book_name)
+    end
+  end
+
   context "preloads virtual_reflection with preloader" do
     it "preloads virtual_reflection (:uses => :books)" do
       expect(preloaded(Author.all.to_a, :named_books)).to preload_values(:named_books, named_books)
     end
 
+    it "preloads virtual_reflection ([:books])" do
+      expect(preloaded(Author.all.to_a, :books)).to preload_values(:named_books, named_books)
+      expect(preloaded(Author.all.to_a, [:books])).to preload_values(:named_books, named_books)
+      expect(preloaded(Author.all.to_a, :books => {})).to preload_values(:named_books, named_books)
+    end
+
     it "preloads virtual_reflection (:uses => {:books => :author_name})" do
       expect(preloaded(Author.all.to_a, :books_with_authors)).to preload_values(:books_with_authors, named_books)
     end