在Rails中尽早碾碎N+1查询

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
# spec/shared_contexts/bulletify.rb
RSpec.shared_context "bullet" do
  before(:each) do
    Bullet.enable = true
    Bullet.bullet_logger = true
    Bullet.raise = true # raise an error if N+1 query occurs
    Bullet.start_request
  end

  after(:each) do
    Bullet.perform_out_of_channel_notifications if Bullet.notification?
    Bullet.end_request
    Bullet.enable = false
    Bullet.bullet_logger = false
    Bullet.raise = false
  end
end

RSpec.configure do |config|
  config.include_context "bullet", bullet: true
  config.alias_example_to :bulletify, bullet: true
end

# spec/controllers/my_controller_spec.rb
context "N+1" do
  bulletify { get :index }
end

1
2
3
4
5
6
7
8
# user.rb
class User < ApplicationRecord
  has_many :teams

  def supports?(team_name)
    teams.where(name: team_name).exists?
  end
end

1
2
3
4
5
6
7
8
# users_controller_spec.rb
describe "GET #index" do
  render_views

  let!(:users) { create_pair(:user, :with_teams) }

  bulletify { get :index }
end

1
2
3
4
5
6
7
8
9
10
11
context "N+1", :n_plus_one do
  # Populate block is called multiple times
  # with different values of n (2 and 3 by default)
  populate { |n| create_list(:user, n, :with_teams) }

  specify do
    # The example body is executed
    #after each `populate` call
    expect { get :index }.to perform_constant_number_of_queries
  end
end

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
# This example uses Minitest
class PerformanceTest < ApplicationIntegrationTestCase
  def populate(scale_factor)
    scale_factor.times do
      # Here, I'm not using create_list but introducing some
      # randomness instead.
      # That would make our setup less deterministic
      # (and, thus, test more valuable)
      create(:resource, :with_tags, tags_num: [0, 1, 2].sample)
    end
    create_list(:document, scale_factor)
  end

  test "should not produce N+1 queries" do
    assert_perform_constant_number_of_queries do
      get :index
    end
  end
end