Error Catching Rails
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the Stack Overflow Community Stack Overflow is a community of 4.7 million programmers, just like you, helping each other. Join them; it only takes a minute: Sign up Catch all exceptions in
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a rails controller up vote 58 down vote favorite 27 Is there a way to catch all uncatched exceptions in a rails controller, like this: def delete schedule_id = params[:scheduleId] begin Schedules.delete(schedule_id) rescue ActiveRecord::RecordNotFound render :json => "record not found" rescue ActiveRecord::CatchAll #Only comes in here if nothing else catches the error end render :json => "ok" end Thank you ruby-on-rails share|improve this question edited ruby on rails error handling Sep 12 '10 at 8:39 George Jempty 5,478948111 asked Sep 12 '10 at 8:01 Neigaard 1,06642244 add a comment| 5 Answers 5 active oldest votes up vote 55 down vote accepted begin # do something dodgy rescue ActiveRecord::RecordNotFound # handle not found error rescue ActiveRecord::ActiveRecordError # handle other ActiveRecord errors rescue # StandardError # handle most other errors rescue Exception # handle everything else end share|improve this answer answered Sep 12 '10 at 8:36 Chris Johnsen 99.3k19142155 12 Isn't the rule to NEVER catch Exception? –RonLugge Nov 18 '14 at 1:13 1 but how can I catch all type in rescue => e block only? –Matrix Feb 19 '15 at 15:03 1 @RonLugge it depends entirely on the situation at hand. applying "never" as a rule of thumb is a bad idea. –Justin Skiles Feb 25 '15 at 0:04 5 @JustinSkiles Catching Exception will catch syntax errors (and interrupt signals too). Give me one good scenario for doing that in production code. Catching signals directly I can get, but you'd need to do so explicitly to make it clear you're creating a signal handler. Just catching Exception... bad, bad ide
those solutions. Let me walk you through the possibilities. begin/rescue block begin/rescue blocks are the standard ruby mechanism to deal with exceptions. It might look like this: begin
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do_something rescue handle_exception end This works nice for exceptions that might happen in rails .find error handling your code. But what if you want to rescue every occurrence of a specific exception, say a NoPermissionError which rails exception message might be raised from your security layer? Clearly you do not want to add a begin/rescue block in all your actions just to render an error message, right? Around filter An around http://stackoverflow.com/questions/3694153/catch-all-exceptions-in-a-rails-controller 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 yield rescue NoPermissionError redirect_to 'permission_error' end end end rescue_from rescue_from gives you the same possibilities as the around https://blog.simplificator.com/2015/03/13/handling-errors-in-ruby-on-rails/ 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: action = ExceptionsController.action(:render_error) action.call(env) In any case you want to set following configuration for exceptions_app to be used: Rails.application.config.consider_all_requests_local = false Rails.application.config.action_dispatch.show_exceptions = true But where is the exception you ask? It is stored in the Rack env: env[ users never enter incorrect data, and resources are plentiful and cheap. Well, that's about to change. Welcome to the real world! In the real world, errors happen. Good programs (and http://phrogz.net/programmingruby/tut_exceptions.html programmers) anticipate them and arrange to handle them gracefully. This isn't always as easy as it might be. Often the code that detects an error does not have the context to know http://www.tutorialspoint.com/ruby-on-rails-2.1/rails-exception-handling.htm what to do about it. For example, attempting to open a file that doesn't exist is acceptable in some circumstances and is a fatal error at other times. What's your file-handling module error handling to do? The traditional approach is to use return codes. The open method returns some specific value to say it failed. This value is then propagated back through the layers of calling routines until someone wants to take responsibility for it. The problem with this approach is that managing all these error codes can be a pain. If a function calls open, then read, rails error handling and finally close, and each can return an error indication, how can the function distinguish these error codes in the value it returns to its caller? To a large extent, exceptions solve this problem. Exceptions let you package up information about an error into an object. That exception object is then propagated back up the calling stack automatically until the runtime system finds code that explicitly declares that it knows how to handle that type of exception. The Exception Class The package that contains the information about an exception is an object of class Exception, or one of class Exception's children. Ruby predefines a tidy hierarchy of exceptions, shown in Figure 8.1. As we'll see later, this hierarchy makes handling exceptions considerably easier. Figure 8.1 not available... When you need to raise an exception, you can use one of the built-in Exception classes, or you can create one of your own. If you create your own, you might want to make it a subclass of StandardError or one of its children. If you don't, your exception won't be caught by default. Every Exception has associated with it a message str Framework Rails 2.1 Dir Structure Rails 2.1 Examples Rails 2.1 Database Setup Rails 2.1 Active Records Rails 2.1 Migrations Rails 2.1 Controllers Rails 2.1 Views Rails 2.1 Layouts Rails 2.1 Scaffolding Rails 2.1 and AJAX Rails 2.1 Uploads Files Rails 2.1 Sends Emails Advanced Ruby on Rails 2.1 Rails 2.1 RMagick Guide Rails 2.1 Basic HTTP Auth Rails 2.1 Error Handling Rails 2.1 Routes System Rails 2.1 Unit Testing Ruby on Rails Quick Guide Rails Quick Guide Ruby Tutorial Ruby Tutorial Ruby on Rails Resources Ruby on Rails Resources Selected Reading Computer Glossary Who is Who Copyright © 2014 by tutorialspoint Home References Discussion Forums About TP Ruby on Rails 2.1 - Exception Handling Advertisements The execution and the exception always go together. If you are opening a file which does not exist then if you did not handle this situation properly then your program is considered to be of bad quality. The program stops if an exception occurs. So exceptions are used to handle various type of errors which may occur during a program execution and take appropriate action instead of halting program completely. Exception handling in Ruby on Rails is similar to exception handling in Ruby. Which means, we enclose the code that could raise an exception in a begin/end block and use rescue clauses to tell Ruby the types of exceptions we want to handle. Syntax : begin # - rescue OneTypeOfException # - rescue AnotherTypeOfException # - else # Other exceptions ensure # Always will be executed end Everything from begin to rescue is protected. If an exception occurs during the execution of this block of code, control is passed to the block between rescue and end. For each rescue clause in the begin block, Ruby compares the raised Exception against each of the parameters in turn. The match will succeed if the exception named in the rescue clause is the same as the type of the currently thrown exception, or is a superclass of that exception. Where to log errors ? There are three option you have when an exception is thrown: log to an internal log file (logger.error). Display an appropriate message to