Error Handling In Ruby Rails
Contents |
& Motion GraphicsBundleseBooksDesign & IllustrationCodeWeb DesignPhoto & VideoBusinessMusic & Audio3D & Motion ruby on rails exception handling GraphicsPricingEnvato MarketEnvato StudioCommunityHelpEnvato MarketEnvato StudioCommunityForumHelpFree 10-Day TrialSign rails error handling best practices InHow-To TutorialsDesign & IllustrationAdobe PhotoshopVectorAdobe IllustratorIllustrationTools & TipsInspirationGraphic DesignNewsIcon DesignDrawingMore Categories...Learning ruby rails flash GuidesCodeWeb DevelopmentWordPressMobile DevelopmentPHPJavaScriptFlashCMSiOS SDKNewsAndroid SDKMore Categories...Learning GuidesWeb DesignCSSHTML & CSSHTMLAdobe PhotoshopUI DesignComplete WebsitesWorkflowDesign TheoryJavaScriptCMSMore Categories...Learning GuidesPhoto & VideoShootingPost-ProcessingAdobe
Ruby On Rails Try Catch
PhotoshopPhoto CritiqueHow-ToPhotographyVideoLightingInspirationAdobe LightroomMore Categories...Learning GuidesBusinessMarketingFreelancePlanningHow-ToCommunicationCareersBusinessSalesEntrepreneurshipFinanceMore Categories...Learning GuidesMusic & AudioAudio ProductionGeneralLogic ProWorkshopsMixing & MasteringSound DesignOpen MicAbleton LiveReasonRecordingMore Categories...Learning Guides3D & Motion GraphicsAdobe After Effects3DMotion Graphics3D Studio MaxMayaCinema 4DWorkflowNewsVisual EffectsRoundupsMore Categories...Learning GuidesGame DevelopmentGame DesignImplementationPlatform AgnosticBusinessProgrammingFlashFrom ScratchNewsHTML5Unity 3DMore rails exception message Categories...Learning GuidesComputer SkillsOS XApp TrainingProductivityTips & ShortcutsElectronicsAutomationSecurityOfficeHow-ToHardwareMore Categories...Learning GuidesCoursesDesign & IllustrationCodeWeb DesignPhoto & VideoBusinessMusic & Audio3D & Motion GraphicsBundlesComing SooneBooksDesign & IllustrationCodeWeb DesignPhoto & VideoBusinessMusic & Audio3D & Motion GraphicsPricingAdvertisementCodeRubyWriting Robust Web Applications - The Lost Art of Exception HandlingAdvertisementby Alan Skorkin6 Jan 2014Languages:EnglishRubyWeb DevelopmentSponsored ContentThis sponsored post features a product relevant to our readers while meeting our editorial guidelines for being objective and educational.As developers, we want the applications we build to be resilient when it comes to failure, but how do you achieve this goal? If you believe the hype, micro-services and a clever communication protocol are the answer to all your prob
Contents Resources Blog Contact Design and Theory Exception and Error Handling How a program recovers from unexpected (and expected) errors Chapter outline Demonstrating exceptions The Begin...Rescue block Flow of exception handling Exception ruby exception handling best practices and Error Classes Further reading Previous Chapter: Image Manipulation Next Chapter: Object-Oriented Concepts Planking
Ruby Exception Class
on the High Line. (Photo by Dan Nguyen) This was a chapter that I decided to include at the last minute. It's
Ruby Raise Custom Exception
not complete but at least you can be aware of basic exception handling. No matter how carefully you code your script, your program is prone to failure for reasons beyond your control. A website that https://code.tutsplus.com/articles/writing-robust-web-applications-the-lost-art-of-exception-handling--net-36395 your script scrapes may suddenly be down. Or someone sharing the same hard drive may delete a file your program is supposed to read from. Circumstances such as these will crash your program. For any kind of long continuous task that you don't want to baby-sit and manually restart, you will need to write some exception-handling code to tell the program how to carry on when things go wrong. Demonstrating exceptions http://ruby.bastardsbook.com/chapters/exception-handling Before the formal description of the the begin/rescue block, let's walk through a couple examples of it in action. At a skin-deep level, it behaves nearly the same as the if/else construct. Skipping past an error The Exception class handles nearly every kind of hiccup that might occur during runtime, including syntax screwups and incorrect type handling. We learned early on that adding numbers and strings with no type conversion would crash a program: a = 10 b = "42" a + b The attempted arithmetic results in this error: The begin/rescue block is typically used on code in which you anticipate errors. There's only one line here for us to worry about: a = 10 b = "42" begin a + b rescue puts "Could not add variables a (#{a.class}) and b (#{b.class})" else puts "a + b is #{a + b}" end Executing the revised code gets us this: Two obvious differences from the first try: The puts statement in the rescue clause executed. And more importantly, the Ruby program did not crash. Let's feed this simple operation with an array of values of different types to see how the else clause comes into play: values = [42, 'a', 'r', 9, 5, 10022, 8.7, "sharon", "Libya", "Mars", "12", 98,
those solutions. Let me walk you through the possibilities. begin/rescue block begin/rescue blocks are the standard ruby mechanism to deal with https://blog.simplificator.com/2015/03/13/handling-errors-in-ruby-on-rails/ exceptions. It might look like this: begin do_something rescue handle_exception end This works nice for exceptions that might happen in your code. But what if you want to rescue https://reinteractive.net/posts/269-exceptional-error-handling-in-ruby every occurrence of a specific exception, say a NoPermissionError which might be raised from your security layer? Clearly you do not want to add a begin/rescue block in all error handling your actions just to render an error message, right? Around filter An around filter could be used to catch all those exceptions of a given class. Honestly I haven't used a before filter for this, this idea came to my mind when writing this blog post. class ApplicationController < ActionController::Base around_action :handle_exceptions private def handle_exceptions begin ruby on rails yield rescue NoPermissionError redirect_to 'permission_error' end end end rescue_from rescue_from gives you the same possibilities as the around filter. It's just shorter and easier to read and if the framework offers a convenient way, then why not use it. There are multiple ways to define a handler for an exception, for a short and sweet handler I prefer the block syntax: class ApplicationController < ActionController::Base rescue_from 'NoPermissionError' do |exception| redirect_to 'permission_error' end end exceptions_app There is an additional feature (added in Rails 3.2) that allows to handle exceptions. You can specify an exceptions_app which is used to handle errors. You can use your own Rails app for this: config.exceptions_app = self.routes If you do so, then your routing must be configured to match error codes like so: match '/404', to: 'exceptions#handle_404' ... Alternatively you can specify a lambda which receives the whole Rack env: config.exceptions_app = lambda do |env| # do something end Do you wonder how you can call an arbitrary action when you have the env? It's pretty easy
handling in Ruby By Yuji Yokoo, 18 December 2015 twitter Scroll down to read I recently come across some surprising code involving exceptions which prompted me to look a bit deeper into exceptions in Ruby. In this post, I would like to share some of what I found. Exception vs StandardError This is where it all started. I had a script that did something like the following (it was not quite this simple, but it shows the important parts): class MyLib class MyLibBaseError < Exception ; end class MyIOError < MyLibBaseError ; end def do_something raise MyIOError rescue puts "logging error: #{$!.message}" # $! is the last exception raised end end Calling do_something results in this: > MyLib.new.do_something MyLib::MyIOError: MyLib::MyIOError from (irb):70:in `do_something' from (irb):76 from /Users/yuji/.rvm/rubies/ruby-2.1.7/bin/irb:11:in `<main>