Too many times I’ve seen people being over-zealous in rescuing their exceptions. They try doing something like this:
def show
@forum = Forum.find(params[:id])
rescue Exception
flash[:notice] = 'The forum you were looking for does not exist'
end
Which will work when it can’t find a forum, and also when you have a typo. Exception the ancestor class of all other exceptions, and so every exception will trigger this rescue. Try making the code look like this:
def show
@forum = Forum.find(params[:id)
rescue Exception
flash[:notice] = 'The forum you were looking for does not exist'
end
and you’ll wonder why a forum is telling you it doesn’t exist when it obviously does! The easiest way to fix this is to rescue correctly. By rescuing correctly, you prevent hours of potential headaches and your code becomes clearer to what it’s doing. In this example, when a forum object can’t be found it will raise the ActiveRecord::RecordNotFound exception, so this is what you should rescue.
def show
@forum = Forum.find(params[:id])
rescue ActiveRecord::RecordNotFound
flash[:notice] = 'The forum you were looking for does not exist'
end
Another situation is when you’re using #save!. This “destructive” version of #save will raise an ActiveRecord::RecordInvalid or ActiveRecord::RecordNotSaved, depending on the kind of validations you have on your model. I use it here in this example:
def create
@topic = @forum.topics.build(params[:topic])
@post = @topic.posts.build(params[:post])
@topic.save!
flash[:notice] = 'Topic has been successfully created'
rescue ActiveRecord::RecordNotSaved, ActiveRecord::RecordInvalid
flash[:notice] = 'Topic could not be created'
ensure
redirect_to forum_topics_path(@forum)
end
I’ve actually specified two arguments to the rescue method here, the first is ActiveRecord::RecordNotSaved, and the next is ActiveRecord::RecordInvalid. The rescue method uses the splat operator (*), so it can take as many arguments as you can throw at it. I’ve also used another method here ensure. No matter how many exceptions get thrown, the code after the ensure statement will always be ran.
The final thing I would like to cover is rescuing two exceptions, but doing two different things.
def create
@topic = @forum.topics.build(params[:topic])
@post = @topic.posts.build(params[:post])
@topic.save!
flash[:notice] = 'Topic has been successfully created'
rescue ActiveRecord::RecordNotSaved
flash[:notice] = 'Topic could not be created, the record could not be saved'
rescue ActiveRecord::RecordInvalid
flash[:notice] = 'Topic could not be created, the record is invalid'
ensure
redirect_to forum_topics_path(@forum)
end