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Debugging rails

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Slides from Debugging Rails workshop at Boston Ruby Project Night

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Debugging rails

  1. 1. Debugging RailsMichael DenomyBoston Ruby Project NightMarch 5, 2013
  2. 2. Agenda• Introduction to Rails Debugging - Role of testing - Examining the log files - Interpreting the stack trace - The better_errors gem - Rails console - Using pry gem to debug
  3. 3. Testing• First line of defense - Avoid defects in the first place• Since adopting TDD, time spent ‣ using a debugger ‣ writing log messages ‣ triaging defectshave all dropped significantly• Find a defect? - First step: write a test to reproduce it
  4. 4. General Debugging Tips• Reproduce the problem - Under what conditions does it occur ‣ data, configuration, environment - Write a unit/integration test if possible• Divide and Conquer - Reduce the places you have to look ‣ Logging statements ‣ Simplest conditions to reproduce ‣ Any recent changes?
  5. 5. General Debugging Tips• Pay attention to the data - Don’t jump to conclusions - Avoid “that can’t be the problem”• Be methodical - Talk the problem out ‣ Use “rubber ducky debugging” if solo - Change one thing at a time - Keep track of changes/ideas you’ve tried out - Periodically circle back and re-evaluate
  6. 6. Rails Log Files• Rails keeps log file for each environment - e.g. development.log, production.log• Log messages have severity levels - :debug, :info, :warn, :error, :fatal - config.log.level filters what gets logged• Writing your own log messages
  7. 7. Asset Pipeline Log Messages• Lots of messages related to asset pipeline• quiet_assets gem - suppresses asset pipeline messages - should be used in development only• thin web server - fixes a problem with message that shows up with quiet_assets gem and WEBrick• Gemfile
  8. 8. Reading A Stack Trace
  9. 9. The better_errors gem• Richer error page ‣ Full stack trace ‣ Source code inspection for all stack frames ‣ Local and instance variable inspection ‣ Live REPL on every stack frame• Advanced features requires ‘binding_of_caller’ gem• Gemfile - Development only!
  10. 10. Using the Rails Console• Great playground to experiment - Especially handy for model access• Danger!!! - Good idea to run in sandbox to prevent changing data rails console --sandbox
  11. 11. pry gem• pry is an IRB replacement - live help - syntax highlighting - navigate scope - and much, much, more• pry also supports plugins...lots of them - check out www.rubygems.org for full list• pry-debugger gem - step, next, continue
  12. 12. Debug Using an IDE• If you come from a background where you have used an IDE, e.g. Java or C#, an IDE is an option• RubyMine has an integrated debugger - Does not play well with pry-debug or other debuggers
  13. 13. Summary• Divide and Conquer Strategy• Be methodical• Check the logs for clues• Testing is the best defense• Questions?
  14. 14. Referenceshttp://gipsysoft.com/articles/debug-rules/http://pryrepl.org/screencasts.htmlhttp://railscasts.com/episodes/86-logging-variableshttp://railscasts.com/episodes/24-the-stack-tracehttp://railscasts.com/episodes/280-pry-with-railshttp://samuelmullen.com/2012/07/getting-more-out-of-the-rails-console/
  15. 15. Debugging RailsMichael DenomyBoston Ruby Project NightMarch 5, 2013

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