ActiveRecord::Associations::Preloader should preload all instances of the same record

activerecord/lib/active_record/associations/preloader.rb

@@ -88,7 +88,6 @@ def preload(records, associations, preload_scope = nil)
         if records.empty?
           []
         else
-          records.uniq!
           Array.wrap(associations).flat_map { |association|
             preloaders_on association, records, preload_scope
           }

activerecord/test/cases/associations/has_many_through_associations_test.rb

@@ -71,6 +71,15 @@ def test_preload_sti_middle_relation
                  club1.members.sort_by(&:id)
   end
 
+  def test_preload_multiple_instances_of_the_same_record
+    club = Club.create!(name: "Aaron cool banana club")
+    Membership.create! club: club, member: Member.create!(name: "Aaron")
+    Membership.create! club: club, member: Member.create!(name: "Bob")
+
+    preloaded_clubs = Club.joins(:memberships).preload(:membership).to_a
+    assert_no_queries { preloaded_clubs.each(&:membership) }
+  end
+
   def test_ordered_has_many_through
     person_prime = Class.new(ActiveRecord::Base) do
       def self.name; "Person"; end