An illustration of counter_cache and optimistic locking incompatiblity

counter_cache_test.rb

require 'active_record'
require 'minitest/autorun'
require 'sqlite3'
require 'logger'

# This connection will do for database-independent bug reports.
ActiveRecord::Base.establish_connection 'sqlite3::memory:'

ActiveRecord::Schema.define do
  create_table :people do |t|
    t.string :name
    t.integer :lock_version, null: false, default: 0
    t.integer :vehicles_count, null: false, default: 0
    t.integer :jobs_count, null: false, default: 0
    t.timestamps
  end

  create_table :jobs do |t|
    t.belongs_to :person
  end

  create_table :vehicles do |t|
    t.belongs_to :owner, polymorphic: true
  end
end

class Person < ActiveRecord::Base
  has_many :jobs,                 dependent: :destroy, counter_cache: true
  has_many :vehicles, as: :owner, dependent: :destroy, counter_cache: true
end

class Job < ActiveRecord::Base
  belongs_to :person, counter_cache: true
end

class Vehicle < ActiveRecord::Base
  belongs_to :owner, polymorphic: true, counter_cache: true
end

class BugTest < Minitest::Test
  def test_locking_dependent_destroy_with_counter_cache
    person = Person.create!
    person.jobs << Job.create!
    assert_equal 1, Person.find(person.id).jobs_count, "Should update the vehicle count after <<"

    assert_equal 1, Person.find(person.id).lock_version, "Should bump the lock version in the database"
    assert_equal 1, person.lock_version, "Should bump the lock version in the loaded model"

    person.destroy
  end

  def test_locking_dependent_destroy_with_counter_cache_and_empty
    person = Person.create!
    person.jobs << Job.create!
    assert_equal 1, Person.find(person.id).jobs_count, "Should update the vehicle count after <<"

    person.jobs = []
    assert_equal 0, Person.find(person.id).jobs_count, "Should update the vehicle count after = []"

    assert_equal 2, Person.find(person.id).lock_version, "Should bump the lock version in the database"
    assert_equal 2, person.lock_version, "Should bump the lock version in the loaded model"

    person.destroy
  end

  def test_locking_polymorphic_dependent_destroy_with_counter_cache
    person = Person.create!
    person.vehicles << Vehicle.create!
    assert_equal 1, Person.find(person.id).vehicles_count, "Should update the vehicle count after <<"

    assert_equal 1, Person.find(person.id).lock_version, "Should bump the lock version in the database"
    assert_equal 1, person.lock_version, "Should bump the lock version in the loaded model"

    person.destroy
  end

  def test_locking_polymorphic_dependent_destroy_with_counter_cache_and_empty
    person = Person.create!
    person.vehicles << Vehicle.create!
    assert_equal 1, Person.find(person.id).vehicles_count, "Should update the vehicle count after <<"
    person.vehicles = []
    assert_equal 0, Person.find(person.id).vehicles_count, "Should update the vehicle count after = []"

    assert_equal 2, Person.find(person.id).lock_version, "Should bump the lock version in the database"
    assert_equal 2, person.lock_version, "Should bump the lock version in the loaded model"

    person.destroy
  end
end

output.txt

-- create_table(:people)
   -> 0.0070s
-- create_table(:jobs)
   -> 0.0007s
-- create_table(:vehicles)
   -> 0.0003s
Run options: --seed 44895

# Running:

FFFF

Finished in 0.045250s, 88.3978 runs/s, 198.8950 assertions/s.

  1) Failure:
BugTest#test_locking_polymorphic_dependent_destroy_with_counter_cache [counter_cache_test.rb:69]:
Should update the vehicle count after <<.
Expected: 1
  Actual: 0


  2) Failure:
BugTest#test_locking_dependent_destroy_with_counter_cache_and_empty [counter_cache_test.rb:61]:
Should bump the lock version in the loaded model.
Expected: 2
  Actual: 0


  3) Failure:
BugTest#test_locking_dependent_destroy_with_counter_cache [counter_cache_test.rb:47]:
Should bump the lock version in the loaded model.
Expected: 1
  Actual: 0


  4) Failure:
BugTest#test_locking_polymorphic_dependent_destroy_with_counter_cache_and_empty [counter_cache_test.rb:80]:
Should update the vehicle count after <<.
Expected: 1
  Actual: 0

4 runs, 9 assertions, 4 failures, 0 errors, 0 skips