Add query count test examples

Author: cema-sp

017_query_count.rb

@@ -0,0 +1,105 @@
+require 'rubygems'
+require 'bundler/inline'
+
+gemfile(true) do
+  source 'https://rubygems.org'
+  gem 'activesupport'
+  gem 'activerecord'
+  gem 'pg'
+end
+
+require 'active_record'
+
+puts "Loaded gems"
+
+class Migration < ActiveRecord::Migration[5.0]
+  def up
+    create_table :things do |t|
+      t.string :col0
+      t.string :col1
+      t.string :col2
+      t.string :col3
+      t.string :col4
+    end
+
+    create_table :minions do |t|
+      t.integer :thing_id
+      t.string :name
+    end
+
+    sql = <<-END
+      INSERT INTO
+        things(col0, col1, col2, col3, col4)
+        (SELECT
+          rpad('x', 100, 'x'),
+          rpad('x', 100, 'x'),
+          rpad('x', 100, 'x'),
+          rpad('x', 100, 'x'),
+          rpad('x', 100, 'x')
+        FROM generate_series(1, 100)
+        );
+    END
+
+    ActiveRecord::Base.connection.execute sql
+  end
+
+  def down
+    drop_table :things
+    drop_table :minions
+  end
+end
+
+class Thing < ActiveRecord::Base
+  has_many :minions
+end
+
+class Minion < ActiveRecord::Base
+  belongs_to :thing
+end
+
+def migrate(dir = :up)
+  Migration.new.migrate(dir)
+end
+
+def track_queries
+  results = []
+  ActiveSupport::Notifications.subscribe('sql.active_record') do |*args|
+    event = ActiveSupport::Notifications::Event.new(*args)
+    query_name = event.payload[:name]
+
+    next if %w(SCHEMA).include? query_name # skip schema lookups
+    results << query_name
+  end
+  yield
+  ActiveSupport::Notifications.unsubscribe('sql.active_record')
+  results
+end
+# ------ main ------
+
+ActiveRecord::Base.establish_connection(
+  adapter: 'postgresql',
+  database: '017_things',
+  host: 'localhost',
+  username: 'postgres'
+)
+
+cmd = ARGV[0]
+
+case cmd
+when '--migrate'
+  migrate(:up)
+when '--rollback'
+  migrate(:down)
+when '--each'
+  puts "Queries:\n"
+  puts (track_queries { Thing.limit(10).each { |thing| thing.minions.load } })
+when '--include'
+  puts "Queries:\n"
+  puts (track_queries { Thing.limit(10).includes(:minions).load })
+else
+  puts "No command provided!"
+  exit!(1)
+end
+
+exit!(0)
+

README.md

@@ -280,6 +280,6 @@ Tips:
 * But don't forget to turn on caching and set log level to `:info`
 * Database size may affect your results, so rollback transactions or clear data
 * Write performance test for complex DB queries
-* Test DB queries count and try to reduce it
+* Test DB queries count and try to reduce it (may use *assert_value* gem) (see [017_query_count.rb](017_query_count.rb))
 * Generate enough data for performance test