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-rw-r--r--activerecord/lib/active_record/associations/preloader/through_association.rb9
-rw-r--r--activerecord/test/cases/associations/eager_test.rb6
2 files changed, 13 insertions, 2 deletions
diff --git a/activerecord/lib/active_record/associations/preloader/through_association.rb b/activerecord/lib/active_record/associations/preloader/through_association.rb
index 24aa47bb51..6c83058202 100644
--- a/activerecord/lib/active_record/associations/preloader/through_association.rb
+++ b/activerecord/lib/active_record/associations/preloader/through_association.rb
@@ -18,7 +18,8 @@ module ActiveRecord
through_records = owners.map do |owner|
association = owner.association through_reflection.name
- [owner, Array(association.reader)]
+ center = target_records_from_association(association)
+ [owner, Array(center)]
end
reset_association owners, through_reflection.name
@@ -49,7 +50,7 @@ module ActiveRecord
rhs_records = middles.flat_map { |r|
association = r.association source_reflection.name
- association.reader
+ target_records_from_association(association)
}.compact
rhs_records.sort_by { |rhs| record_offset[rhs] }
@@ -91,6 +92,10 @@ module ActiveRecord
scope
end
+
+ def target_records_from_association(association)
+ association.loaded? ? association.target : association.reader
+ end
end
end
end
diff --git a/activerecord/test/cases/associations/eager_test.rb b/activerecord/test/cases/associations/eager_test.rb
index 0c09713971..874d53c51f 100644
--- a/activerecord/test/cases/associations/eager_test.rb
+++ b/activerecord/test/cases/associations/eager_test.rb
@@ -1402,4 +1402,10 @@ class EagerAssociationTest < ActiveRecord::TestCase
post = Post.eager_load(:tags).where('tags.name = ?', 'General').first
assert_equal posts(:welcome), post
end
+
+ # CollectionProxy#reader is expensive, so the preloader avoids calling it.
+ test "preloading has_many_through association avoids calling association.reader" do
+ ActiveRecord::Associations::HasManyAssociation.any_instance.expects(:reader).never
+ Author.preload(:readonly_comments).first!
+ end
end