Anatomy of a gem: DatabaseCleaner

Ernesto Tagwerker Founder, Ombu Labs @etagwerker

DatabaseCleaner: Strategies for cleaning databases

https://github.com/ DatabaseCleaner/ database_cleaner

# Gemfile group :test do gem 'database_cleaner' end # spec_helper.rb require 'database_cleaner' RSpec.configure do |config| config.before(:suite) do DatabaseCleaner.strategy = :truncation DatabaseCleaner.clean_with(:truncation) end config.around(:each) do |example| DatabaseCleaner.cleaning do example.run end end end Setup

RSpec.configure do |config| config.before(:suite) do DatabaseCleaner.strategy = :truncation, { except: %w(states countries) } DatabaseCleaner.clean_with(:truncation) end config.around(:each) do |example| DatabaseCleaner.cleaning do example.run end end end Setup with exceptions

RSpec.configure do |config| config.before(:suite) do DatabaseCleaner[:active_record].strategy = :transaction DatabaseCleaner[:mongo_mapper].strategy = :truncation DatabaseCleaner[:active_record].clean_with(:transaction) DatabaseCleaner[:mongo_mapper].clean_with(:truncation) end config.around(:each) do |example| DatabaseCleaner.cleaning do example.run end end end Setup with multiple ORMs

Strategies: • Truncation • Transaction • Deletion

ORM: • ActiveRecord • Sequel • Ohm • … and six more

It works with: • Cucumber • RSpec • Minitest

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Complexity

Too many combinations: Drivers + ORMs + Database + Strategies

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# configuration.rb module DatabaseCleaner class NoORMDetected < StandardError; end class UnknownStrategySpecified < ArgumentError; end class << self def [](orm, opts = {}) raise NoORMDetected unless orm init_cleaners # TODO: deprecate # this method conflates creation with lookup. if @cleaners.has_key? [orm, opts] @cleaners[[orm, opts]] else add_cleaner(orm, opts) end end Configuration.[]

module DatabaseCleaner class << self def clean_with(*args) connections.each { |connection| connection.clean_with(*args) } end def connections # double yuck.. can't wait to deprecate this whole class... unless defined?(@cleaners) && @cleaners autodetected = ::DatabaseCleaner::Base.new add_cleaner(autodetected.orm) end @connections end Configuration.connections

module DatabaseCleaner class Base def autodetect_orm if defined? ::ActiveRecord :active_record elsif defined? ::DataMapper :data_mapper ...… elsif defined? ::Moped :moped elsif defined? ::Ohm :ohm elsif defined? ::Redis :redis elsif defined? ::Neo4j :neo4j end end Base#autodetect_orm

module DatabaseCleaner class Base def start strategy.start end def clean strategy.clean end alias clean! clean def cleaning(&block) strategy.cleaning(&block) end DatabaseCleaner::Base (start, clean, cleaning)

module ::DatabaseCleaner module Generic module Base def cleaning(&block) begin start yield ensure clean end end DatabaseCleaner::Generic::Base

module Truncation OPTS = [:only, :except, :pre_count, :reset_ids, :cache_tables] def initialize(opts={}) if !opts.empty? && !(opts.keys - OPTS).empty? msg = <<-EOS The only valid options are #{OPTS.join(', ')}. You specified #{opts.keys. join(',')}. EOS raise ArgumentError, msg end if opts.has_key?(:only) && opts.has_key?(:except) raise ArgumentError, "You may only specify either :only or :except." end @only = opts[:only] @tables_to_exclude = Array((opts[:except] || []).dup).flatten @tables_to_exclude += migration_storage_names @pre_count = opts[:pre_count] @reset_ids = opts[:reset_ids] @cache_tables = opts.has_key?(:cache_tables) ? !!opts[:cache_tables] : true end DatabaseCleaner::Generic::Truncation

module DatabaseCleaner module Generic module Truncation # ... def start # included for compatibility reasons, # do nothing if you don't need to end def clean raise NotImplementedError end Generic Public Interface

require "database_cleaner/generic/truncation" require “database_cleaner/active_record/base" module DatabaseCleaner module ConnectionAdapters module AbstractAdapter def truncate_table(table_name) raise NotImplementedError end def truncate_tables(tables) tables.each do |table_name| self.truncate_table(table_name) end end end DatabaseCleaner::ActiveRecord::Truncation

module DatabaseCleaner module ConnectionAdapters # ... module AbstractMysqlAdapter def truncate_table(table_name) execute("TRUNCATE TABLE #{quote_table_name(table_name)};") end # ... module IBM_DBAdapter def truncate_table(table_name) execute("TRUNCATE #{quote_table_name(table_name)} IMMEDIATE") end end # ... module PostgreSQLAdapter def truncate_tables(table_names) return if table_names.nil? || table_names.empty? execute("TRUNCATE TABLE #{table_names.map{|name| quote_table_name(name)}. join(', ')} #{restart_identity} #{cascade};") end DatabaseCleaner::ActiveRecord::Truncation

Roadmap (v2.0)

• Split DatabaseCleaner into smaller gems • Change setup interface • Reduce complexity of configuration.rb & base.rb • Release v1.99 with deprecation warnings • Make it easier for people to write their own strategies • Look for more maintainers

# Gemfile group :test do gem ‘database_cleaner-active_record’ end # spec_helper.rb require ‘database_cleaner/active_record’ RSpec.configure do |config| config.before(:suite) do DatabaseCleaner.strategy = :truncation DatabaseCleaner.clean_with(:truncation) end config.around(:each) do |example| DatabaseCleaner.cleaning do example.run end end end Setup for ActiveRecord (v2.0)

# running the build bundle exec rspec spec/ # you will get this message database_cleaner 2 will no longer automatically detect your ORM. You must explicitly require the right path: # spec_helper.rb require ‘database_cleaner/active_record’ # Gemfile group :test do gem ‘database_cleaner-active_record’ end If you wish to upgrade to database_cleaner 2.0+, you must change this in your project. Deprecation Warnings (v1.99)

DatabaseCleaner v2.0 https://github.com/ DatabaseCleaner/ database_cleaner/tree/2-0

DatabaseCleaner- e.g. https://github.com/ DatabaseCleaner/ database_cleaner-active_record

Thank you!

Questions?