Do not belittle rake tasks

Transcript

1. Do Not Belittle Rake Tasks Mateusz Bielec RRUG #16, 06.11.2018
2. What is a rake task? • Just a script to run at any time in a console • Common Rails tasks: ◦ rake db:reset, rake db:create, rake db:migrate ◦ rake -T ◦ rake routes • Custom task: desc 'Rake task description' task :name_of_task do # Your code goes here end
3. When we use custom rake tasks? • Script automation • Data cleanup • Long database migration
4. Why is it important to write a good custom rake task? • Usually it’s production code • Readability • Maintainability • Testing • Transparency
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6. My list of the things to consider • Size of .rake file • Idempotency • Tracking progress • Logging the work • Isolated structure • Testing • The performance
7. * without the boilerplate
8. Ideal .rake file namespace :mailchimp desc 'Import users from Mailchimp' task import_users: :environment do Mailchimp::ImportUsers.call end end
9. Keep .rake file as small as possible namespace :mailchimp desc 'Import users from Mailchimp' task :import_users do puts 'Importing users from Mailchimp' result = Mailchimp::ImportUsers.call puts "Successfully imported #{result} users!" end end
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11. Idempotency • It’s important on cleanups and migrations • Can be easily fulfilled with: ◦ a good query ◦ modifying the input file ◦ omitting already created data
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13. Tracking progress • The task executor needs to know the current status of the task • Show anything ◦ from dots ◦ to printing a line for each processed item • Or use a gem ProgressBar:
14. ProgressBar gem namespace :cleanup desc 'Cleanup bad fees' task :fix_bad_fees do query = Cleanup::FixBadFees::Query.call progress_bar = ProgressBar.create( title: 'Fixing bad fees by adding a discount', total: query.count ) # ... end end namespace :cleanup desc 'Cleanup bad fees' task :fix_bad_fees do # ... result = Cleanup::FixBadFees::Task.call(query: query) do progress_bar.increment end puts "Successfully fixed #{result} fees!" end end
15. ProgressBar gem class Cleanup::FixBadFees::Task def self.call(*args, &block) new.self(*args, &block) end def call(query:) query.find_each do # Fix bad fees yield if block_given? end end end
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17. Logging • Who performed the task? When? Why? • Log the action ◦ Notes ◦ Audit trail ◦ History events • Log the task’s execution • Include the executor ◦ TASK_EXECUTOR=jon.snow@westeros rake kill_undead
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19. Isolated structure • .rake files usually in /lib/tasks • The rest in /app/tasks • Each task in a separated module
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21. Testing custom rake tasks • Automated tests class for each PORO class used in a rake task • No automated tests for .rake file, rely on manual testing • Don’t be lazy
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23. Performance • Predict the scale at the very beginning • Define bottlenecks ◦ Reading from large file or from multiple database tables ◦ Calling external services ◦ Saving many rows to the database • Use database close to production (locally, staging)
24. Summary • Rake task are a part of our application • Bad task may cause a lot of damage • With a little of effort we can do it right
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