101 lines
2.9 KiB
Markdown
101 lines
2.9 KiB
Markdown
+++
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date = "2011-10-14"
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title = "Rails 3: Customized exception handling"
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tags = ["Rails", "rails3", "exceptions", "error", "rescue"]
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slug = "rails-3-customized-exception-handling"
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+++
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Exceptions happen. There's no way around that. But not all exceptions are created equally.
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For instance, a 404 "Not found" error can (and should) be handled correctly in your application.
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Let me give you an example of how to handle a `ActiveRecord::RecordNotFound` exception. Let's assume you have an application that could show a user profile:
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``` ruby
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# GET /p/:name
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def show
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@profile = Profile.find(params[:name])
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end
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```
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Now, it may happen that the `:name` paramater contains a value that cannot be found in our database, most likely because someone made a typo in the URL.
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If `Profile#find` cannot get a proper result it will throw `ActiveRecord::RecordNotFound`.
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Now, instead of showing the user the (by default ugly) 404 page from `public/404.html` we want to do something more fancy.
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## Action-specific exception handling
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Here's one solution:
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``` ruby
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# GET /p/:name
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def show
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@profile = Profile.find(params[:name])
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rescue
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render :template => 'application/profile_not_found', :status => :not_found
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end
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```
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You can now create `app/views/applicaiton/profile_not_found.html.haml` and give a nice custom error message to your user.
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You may try to find some matching profiles to `:name` or show a search box.
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## Global exception handling
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The above example only works for the specific profile `show` action. It's also possible to hanlde exceptions on the application level.
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Your `show` action still looks like this:
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``` ruby
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# GET /p/:name
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def show
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@profile = Profile.find(params[:name])
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end
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```
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Then, in your `app/controllers/application_controller.rb` add this:
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``` ruby
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class ApplicationController < ActionController::Base
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rescue_from ActiveRecord::RecordNotFound, :with => :rescue_not_found
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protected
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def rescue_not_found
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render :template => 'application/not_found', :status => :not_found
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end
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end
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```
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Whenever an `ActiveRecord::RecordNotFound` exception is thrown (and not handled by the action itself), it will be handled by your `ApplicationController`.
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## Custom exceptions
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It's possible to throw your own custom exceptions and handle them in different ways. Like this:
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``` ruby
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# Define your own error
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class MyApp::ProfileNotFoundError < StandardError
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end
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# GET /p/:name
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def show
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@profile = Profile.find_by_name(params[:name])
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raise MyApp::ProfileNotFoundError if @profile.nil?
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end
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```
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And add this to your `ApplicationController`:
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``` ruby
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rescue_from MyApp::ProfileNotFoundError, :with => :profile_not_found
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```
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Optionally, if you don't want to write that custom `profile_not_found` method, you may also supply a block:
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``` ruby
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rescue_from MyApp::ProfileNotFoundError do |exception|
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render :nothing => "Profile not found.", :status => 404
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end
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```
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