prior association method call for has_one relation fires unwanted select query after save

[mtoygar]

Steps to reproduce

• a foo record with a has_one association named bar
• call foo.association(:bar)
• call foo.save!
• it fires a select request for the bar relation

# frozen_string_literal: true

require "bundler/inline"

gemfile(true) do
  source "https://rubygems.org"

  git_source(:github) { |repo| "https://github.com/#{repo}.git" }

  gem "activerecord", "~> 7.0.0.alpha2"
  gem "sqlite3"
end

require "active_record"
require "logger"

ActiveRecord::Base.establish_connection(adapter: "sqlite3", database: ":memory:")
ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  create_table :bars, force: true do |t|
    t.integer :foo_id
  end

  create_table :foos, force: true do |t|
    t.string :name
  end
end

puts <<~EOF
############################
############################
## DB setup is completed. ##
############################
############################
EOF

class Bar < ActiveRecord::Base
  belongs_to :foo
end

class Foo < ActiveRecord::Base
  has_one :bar
end

def with_association_call
  foo = Foo.create!

  foo.name = 'new one'
  foo.association(:bar)
  foo.save!
end

def without_association_call
  foo = Foo.create!

  foo.name = 'new one'
  foo.save!
end

puts 'with_association_call'
with_association_call
puts 'without_association_call'
without_association_call 

# below is the output of this script, with_association_call fires an unwanted select query for bar association

with_association_call
D, [2021-09-24T17:28:13.637181 #50914] DEBUG -- :   TRANSACTION (0.0ms)  begin transaction
D, [2021-09-24T17:28:13.637389 #50914] DEBUG -- :   Foo Create (0.1ms)  INSERT INTO "foos" DEFAULT VALUES
D, [2021-09-24T17:28:13.637630 #50914] DEBUG -- :   TRANSACTION (0.0ms)  commit transaction
D, [2021-09-24T17:28:13.643616 #50914] DEBUG -- :   TRANSACTION (0.0ms)  begin transaction
D, [2021-09-24T17:28:13.643829 #50914] DEBUG -- :   Foo Update (0.1ms)  UPDATE "foos" SET "name" = ? WHERE "foos"."id" = ?  [["name", "new one"], ["id", 1]]
D, [2021-09-24T17:28:13.647662 #50914] DEBUG -- :   Bar Load (0.1ms)  SELECT "bars".* FROM "bars" WHERE "bars"."foo_id" = ? LIMIT ?  [["foo_id", 1], ["LIMIT", 1]]
D, [2021-09-24T17:28:13.647816 #50914] DEBUG -- :   TRANSACTION (0.0ms)  commit transaction
without_association_call
D, [2021-09-24T17:28:13.648166 #50914] DEBUG -- :   TRANSACTION (0.0ms)  begin transaction
D, [2021-09-24T17:28:13.648294 #50914] DEBUG -- :   Foo Create (0.1ms)  INSERT INTO "foos" DEFAULT VALUES
D, [2021-09-24T17:28:13.648436 #50914] DEBUG -- :   TRANSACTION (0.0ms)  commit transaction
D, [2021-09-24T17:28:13.648743 #50914] DEBUG -- :   TRANSACTION (0.0ms)  begin transaction
D, [2021-09-24T17:28:13.648890 #50914] DEBUG -- :   Foo Update (0.1ms)  UPDATE "foos" SET "name" = ? WHERE "foos"."id" = ?  [["name", "new one"], ["id", 2]]
D, [2021-09-24T17:28:13.649011 #50914] DEBUG -- :   TRANSACTION (0.0ms)  commit transaction

Expected behavior

with_association_call should not fire SELECT "bars".* FROM "bars" WHERE "bars"."foo_id" = ? LIMIT ? query

Actual behavior

with_association_call fires the query

System configuration

Rails version: 7.0.0.alpha2
Ruby version: ruby 2.7.2p137 (2020-10-01 revision 5445e04352) [x86_64-darwin20]

Some ideas about what happens here

I believe the error stems from the implementation of the below save_has_one_association method.

rails/activerecord/lib/active_record/autosave_association.rb

Lines 435 to 461 in 1268b9a

	def save_has_one_association(reflection)
	association = association_instance_get(reflection.name)
	record = association && association.load_target
	if record && !record.destroyed?
	autosave = reflection.options[:autosave]
	if autosave && record.marked_for_destruction?
	record.destroy
	elsif autosave != false
	key = reflection.options[:primary_key] ? public_send(reflection.options[:primary_key]) : id
	if (autosave && record.changed_for_autosave?) || record_changed?(reflection, record, key)
	unless reflection.through_reflection
	record[reflection.foreign_key] = key
	if inverse_reflection = reflection.inverse_of
	record.association(inverse_reflection.name).inversed_from(self)
	end
	end
	saved = record.save(validate: !autosave)
	raise ActiveRecord::Rollback if !saved && autosave
	saved
	end
	end
	end
	end

An early return like return unless autosave = reflection.options[:autosave] is solving the issue on my local. It seems we dont need to load relation if autosave option is falsy. I'm willing to open a pr if this solution seems plausible to you.

EDIT: We cannot add an early return here as has_one relation wants to save new records by default.
maybe we can add an early return like the one used in save_belongs_to_association 👇 (sth like return unless association && association.loaded?)

rails/activerecord/lib/active_record/autosave_association.rb

Line 481 in 1268b9a

return unless association && association.loaded? && !association.stale_target?

Note: I was not able to reproduce this for has_many and belongs_to relations if that helps.

Also, probably related to #42637. Adding an early return seems to solve that issue as well.

[rails-bot]

This issue has been automatically marked as stale because it has not been commented on for at least three months.
The resources of the Rails team are limited, and so we are asking for your help.
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