Debugging rails
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Testing is the first line of defense when debugging Rails applications. The log files and stack traces provide clues, and gems like better_errors and pry make debugging more powerful. When a defect is found, reproduce it with a test case then use a methodical divide-and-conquer approach, examining the logs, changing one thing at a time, and re-evaluating periodically until the problem is solved.
Debugging rails
- 1. Debugging Rails Michael Denomy Boston Ruby Project Night March 5, 2013
- 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. Testing • First line of defense - Avoid defects in the first place • Since adopting TDD, time spent ‣ using a debugger ‣ writing log messages ‣ triaging defects have all dropped significantly • Find a defect? - First step: write a test to reproduce it
- 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. 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. 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. 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. Reading A Stack Trace
- 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. 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. 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. 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. Summary • Divide and Conquer Strategy • Be methodical • Check the logs for clues • Testing is the best defense • Questions?
- 15. Debugging Rails Michael Denomy Boston Ruby Project Night March 5, 2013