HOW TO EAT A WHALE MAKING THE CHANGES YOU KNOW YOU NEED TO

Have you heard of tiny Melinda Mae, Who ate a monstrous whale? She thought she could, She said she would, So she started in right at the tail. - Shel Silverstein

not a criticism

WE HAVE TO CHANGE

▸ Hard to Maintain ▸ New Features ▸ Better Performance ▸ Security ▸ Ergonomics ▸ Hiring

RAILS 5 AS A CASE STUDY

it’s a common upgrade

▸ 1.2 ➡ 4.2 ▸ 3.0 ➡ 5.0 ▸ 4.2 ➡ 5.0 ▸ 4.2 ➡ 5.0 success success failure ongoing!

this works for other big changes

WHY WE DON’T CHANGE

the changes are ambiguous

the risk is high

it’s a lot of work

source: git log -L 5,6:Gemfile Date Rails Version Jun ‘19 4.2.11 Aug ‘17 4.2.7.1 Dec ‘16 4.2.7 Mar ‘16 4.1.13 Mar ‘16 4.2.5.2 Feb ‘16 4.2.5.1 Aug ‘15 4.1.13 Jan ‘15 4.1.9 Dec ‘14 4.0.0 … … May ‘13 3.2.8

but there is hope!

1. REDUCE AMBIGUITY

try to get a list of changes

▸ changelogs ▸ upgrade guide ▸ gem dependency graph ▸ try changes and see what explodes

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uncover sneaky problems

# old class FactoryGirl # new class FactoryBot

class Money::Arithmetic def ==(other) # don’t allow comparison w/ non-Money objects unless other.is_a? Money || other.zero? raise ArgumentError end # ... do comparison end end

class Money::Arithmetic def ==(other) # warn about problems if other.is_a?(Numeric) && other.nonzero? trigger_warning_and_rollbar end super # run actual comparison end end

keep strong test coverage

2. REDUCE RISK

take tiny steps

‣ rails 5 ‣ factory_bot ‣ belongs_to ‣ protected_attributes ‣ strong params ‣ activeadmin ‣ devise ‣ upgrade ruby ‣ rails 4.2.11 ‣ sass ‣ coffee ‣ money ‣ etc… ‣ quiet_assets*

‣ factory bot ‣ add shim ‣ use shim for existing cases ‣ upgrade factory girl to most recent version ‣ switch to factory bot and remove shim lots of changes, low risk tiny change, highest risk

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update code, then dependency

FactoryBot.define AtlRollout do # ... end

# warning: BigDecimal.new is deprecated; # use BigDecimal() method instead. (BigDecimal.new('-50.00')..BigDecimal.new('50.00')) => 'cold',

# in rails 4, this is optional # in rails 5, it’s required belongs_to :packing_facility # this works in both! belongs_to :packing_facility, required: false

Make the change easy, Then make the easy change. - Kent Beck

surface errors quickly, in the right place

NoMethodError: undefined method 'sellout_limit' for nil:NilClass # ./app/models/meal.rb:531:in 'sellout_limit_for' # ./app/models/menu.rb:254:in 'meal_sold_out?' # ./app/models/meal_selection.rb:208:in 'validate_meal_selection'

ArgumentError: Couldn’t find 3rd meal for plan 'Standard' in menu ’15-jul-2019' (2 meals for plan) # ./spec/factories/weekly_baskets.rb:131:in `validate_selection!' # ./spec/factories/weekly_baskets.rb:61:in `block (5 levels)’ # ./spec/factories/weekly_baskets.rb:58:in `times' # ./spec/factories/weekly_baskets.rb:58:in `block (4 levels)’

3. REDUCE EFFORT

it’s okay to be a bit clever

# in rails 4, this is optional # in rails 5, it’s required belongs_to :packing_facility

WeeklyBasket.reflect_on_all_associations.each do |association| next if association.macro != :belongs_to foreign_key_field = klass.reflections[association.name.to_s].foreign_key column = klass.columns.find { |c| c.name == foreign_key_field.to_s } required = association.options.fetch(:required, true) && !association.options.fetch(:optional, false) if required && column.null exceptions << sprintf(“%-50s required, but column is nullable", "#{klass}##{association.name}") elsif !required && !column.null exceptions << sprintf("%-50s not required, but column is not nullable", "#{klass}##{association.name}") end end

WeeklyBasket.reflect_on_all_associations.each do |association| end next if association.macro != :belongs_to foreign_key_field = klass.reflections[association.name.to_s].foreign_key column = klass.columns.find { |c| c.name == foreign_key_field.to_s } required = association.options.fetch(:required, true) && !association.options.fetch(:optional, false) if required && column.null exceptions << sprintf(“%-50s required, but column is nullable", "#{klass}##{association.name}") elsif !required && !column.null exceptions << sprintf("%-50s not required, but column is not nullable", "#{klass}##{association.name}") end

WeeklyBasket#address will be required, but column is nullable WeeklyBasket#meal_plan will be required, but column is nullable WeeklyBasket#shipping_box will be required, but column is nullable WeeklyBasket#shipping_region will be required, but column is nullable

namespaces and shims

class Money::Arithmetic def ==(other) if other.is_a?(Numeric) && other.nonzero? trigger_warning_and_rollbar end super end end

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namespace :rails_5 do task check_belongs_to_associations: :environment do silence_warnings do print "Eager Loading..." Rails.application.eager_load! puts “done.” # ... do comparison end end end

do the hard work

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MOVING TARGETS: PEOPLE RISKS

it's hard to relearn everything

short lived changes (again)

make it easier to do the right thing

TO SUM THINGS UP

ambiguity happens, risk happens, effort happens. but you minimize them

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THANKS!