Error Handling In Rails 2.3
Web Dev @ Microsoft SEO By WooRank Books Courses Screencasts Newsletters Versioning Shop Forums Advertise Contribute Contact Us Our Story 995kSubscribers 132kFollowers 80kFollowers Ruby Article Ruby Error Handling, Beyond the Basics By Darko Gjorgjievski June 16, 2015 Imagine you're riding a bike. Now, imagine the designers of that bike built it so it rides smoothly only on roads without bumps and encountering one would result in the entire bicycle breaking! You wouldn't want that, would you? Yet this is how thousands of software developers design their software every single day. They put error handling in as an afterthought, dealing with it only when it's inevitable. The truth is, it's not their fault. Most of the material on this subject is very basic, covering simple things like raising an error, rescuing it, different error types and…that's about it. This article will attempt to go deeper than that. I assume you're familiar with the basics of error handling (using raise, begin/rescue, what StandardError is, error inheritance). That's the only prerequisite for reading this article. Let's begin. What Did We Do Before Raising/Handling Exceptions? Before exceptions were invented, the primary method of communication that something in the program has failed was through error return codes. As time passed, people looked at ways to clearly distinguish between what their program does and what would happen if it didn't do what it was supposed to (return codes were far from ideal for this purpose) do. Thus, the invention of language constructs like: raise rescue begin/end (Many other languages use different wording, like try/catch or throw, but the idea behind it remains the same.) There are opposing views to using exceptions and error handling in the first place. Some of these points make sense and we'll discuss them later in the article. For now, let's get you familiar with some of the ways of handling errors in Ruby that can help you manage them better. Cleanup Before Crashing Often we have no idea when our program is going to crash. What if we needed to do some cleanup operations before our program ends (due to an error)? That's where at_exit comes to the rescue: puts 'Hello' at_exit do puts 'Exiting' end raise 'error' This program will print both "Hello" and "Exiting". The code inside at_exit will execute when the program exits (whether it's normally or with an exception). If you want it to run only when an exception is raised, use the global variable $! in Ruby. The default valu
contributors.rdoc dtrace_probes.rdoc extension.ja.rdoc extension.rdoc globals.rdoc keywords.rdoc maintainers.rdoc marshal.rdoc regexp.rdoc security.rdoc standard_library.rdoc syntax.rdoc assignment.rdoc calling_methods.rdoc control_expressions.rdoc exceptions.rdoc literals.rdoc methods.rdoc miscellaneous.rdoc modules_and_classes.rdoc precedence.rdoc refinements.rdoc README.ja.rdoc README.rdoc Class/Module Index Quicksearch ArgumentError Array BasicObject Bignum Binding Class ClosedQueueError Comparable Complex Complex::compatible ConditionVariable Continuation Data Dir ENV EOFError Encoding Encoding::CompatibilityError Encoding::Converter Encoding::ConverterNotFoundError Encoding::InvalidByteSequenceError Encoding::UndefinedConversionError https://www.sitepoint.com/ruby-error-handling-beyond-basics/ EncodingError Enumerable Enumerator Enumerator::Generator Enumerator::Lazy Enumerator::Yielder Errno Exception FalseClass Fiber FiberError File File::Constants File::Stat FileTest Fixnum Float FloatDomainError GC GC::Profiler Hash IO IO::EAGAINWaitReadable IO::EAGAINWaitWritable IO::EINPROGRESSWaitReadable IO::EINPROGRESSWaitWritable IO::EWOULDBLOCKWaitReadable IO::EWOULDBLOCKWaitWritable IO::WaitReadable IO::WaitWritable IOError IndexError Integer Interrupt Kernel KeyError LoadError LocalJumpError Marshal http://ruby-doc.org/core-2.3.0/Exception.html MatchData Math Math::DomainError Method Module NameError NilClass NoMemoryError NoMethodError NotImplementedError Numeric Object ObjectSpace ObjectSpace::WeakMap Proc Process Process::GID Process::Status Process::Sys Process::UID Process::Waiter Queue Random Random::Formatter Range RangeError Rational Rational::compatible Regexp RegexpError RubyVM RubyVM::Env RubyVM::InstructionSequence RuntimeError ScriptError SecurityError Signal SignalException SizedQueue StandardError StopIteration String Struct Symbol SyntaxError SystemCallError SystemExit SystemStackError Thread Thread::Backtrace::Location Thread::Mutex ThreadError ThreadGroup Time TracePoint TrueClass TypeError UnboundMethod UncaughtThrowError ZeroDivisionError fatal unknown No matching classes. Exception Descendants of class Exception are used to communicate between Kernel#raise and rescue statements in begin ... end blocks. Exception objects carry information about the exception – its type (the exception’s class name), an optional descriptive string, and optional traceback information. Exception subclasses may add additional information like NameError#n
Migrations Active Record Validations and Callbacks Active Record Associations Active Record Query http://guides.rubyonrails.org/v2.3.11/activerecord_validations_callbacks.html Interface Views Layouts and Rendering in Rails Action View https://simonecarletti.com/blog/2009/12/inside-ruby-on-rails-rescuable-and-rescue_from/ Form Helpers Controllers Action Controller Overview Rails Routing from the Outside In Digging Deeper Rails Internationalization API Action Mailer Basics Testing Rails Applications Securing Rails Applications Debugging Rails Applications Performance Testing Rails Applications The Basics of error handling Creating Rails Plugins Configuring Rails Applications Rails on Rack Rails Command Line Tools and Rake Tasks Caching with Rails Contributing to Rails Contribute Credits Active Record Validations and Callbacks This guide teaches you how to hook into the lifecycle of your Active Record objects. You will error handling in learn how to validate the state of objects before they go into the database, and how to perform custom operations at certain points in the object lifecycle. After reading this guide and trying out the presented concepts, we hope that you'll be able to: Understand the lifecycle of Active Record objects Use the built-in Active Record validation helpers Create your own custom validation methods Work with the error messages generated by the validation process Create callback methods that respond to events in the object lifecycle Create special classes that encapsulate common behavior for your callbacks Create Observers that respond to lifecycle events outside of the original class Chapters The Object LifecycleValidations OverviewWhy Use Validations? When Does Validation Happen? Skipping Validations valid? and invalid? errors.invalid?Validation Helpersvalidates_acceptance_of validates_associated validates_confirmation_of validates_exclusion_of validates_format_of validates_inclusion_of validates_length_of validates_numericality_of validates_presence_of validates_uniqueness_of validates_e
not apply to different versions. This is article is part of my series Understanding Ruby and Rails. Please see the table of contents for the series to view the list of all posts. Last time I talked about the ActiveSupport Module#delegate method. Today, I want to introduce an other poweful ActiveSupport module: Rescuable, also known in the Rails ecosystem as rescue_from. rescue_from and Rails Starting from the release 2.0, Rails provides a clean way to rescue exceptions in a controller, mapping specific error classes to corresponding handlers. Let's see an example. A call to ActiveRecord#find raises an ActiveRecord::RecordNotFound exception when the record passed as parameter doesn't exist. Assuming you want to display a nice 404 error page, you need to rescue the exception in each action where a find call is performed. class PostsController < ApplicationController def show @post = Post.find(params[:id]) rescue ActiveRecord::RecordNotFound render_404 end def edit @post = Post.find(params[:id]) rescue ActiveRecord::RecordNotFound render_404 end def destroy @post = Post.