[Rails] Re: Hook into Exception Chain

Hi Christoph,

My (simple) example was just trying to give you an idea of how to do what you were asking using rescue_from.

And note that the log does show that the re-raising worked as expected, where we did something with the caught exception first (ie write a debug TEST line to the log) before then re-raising it and letting the rails env stack handle it (ie log shows the stacktrace including the orig line where the bug is in the code, ...).

As for "a better way", it always depends on what you're ultimately trying to accomplish and the tradeoffs for getting there.

But if you really did want to use rescue_from for any/all exceptions/errors that could occur, then at a minimum you're going to want to make sure that what you do with that caught exception (ie your Log4r::MDC... call) doesn't itself result in any exceptions/errors.  One way would be to wrap that work in a begin ... rescue Exception => e2 ... end ... before then re-raising the originally caught exception.

Jeff

On Tuesday, November 12, 2013 11:26:47 AM UTC-8, sol wrote:

Hi Jeff, thanks for your reply!

I found the article here:

http://www.simonecarletti.com/blog/2009/11/re-raise-a-ruby-exception-in-a-rails-rescue_from-statement/

And he mentions that re-raising does not work since rails won't catch it anymore..

has this been changed since?

I generally thought there might be a better way, as usually re-raising exceptions is considered to be bad :)

Thanks a lot,

Christoph

On Tuesday, 12 November 2013 19:07:00 UTC+1, Jeff Lewis wrote:

Hi Christoph,

All you need to do is re-raise the exception after you're done using it in your rescue_from, so something along the lines of:

$ cat ./app/controllers/foo_controller.rb

...

  rescue_from Exception do |e|

    # do something with e before re-raising it ...

    Rails.logger.debug("TEST: before re-raising ... e=#{e.inspect}")

    raise e

  end

...

  def testfoo

    x = 'bar' if 1/0

    ....

  end

....

$ curl -sLi http://foo.localhost/testfoo

...

$ cat ./log/development.log

...

[c55f5] TEST: before re-raising ... e=#<ZeroDivisionError: divided by 0>

[c55f5] Completed 500 Internal Server Error in 17ms

[c55f5]

ZeroDivisionError (divided by 0):

  app/controllers/foo_controller.rb:89:in `/'

  app/controllers/foo_controller.rb:89:in `testfoo'

...

Jeff

On Tuesday, November 12, 2013 6:40:12 AM UTC-8, sol wrote:

Hi there,

I'm using Log4r in my rails projects. On log.error an email is sent using the EmailOutputter.

I know changed the EmailOutputter to include a global var in the subject (MDC) since the subject is normally static.

I want to set this var to the exception message, so it is sent as the subject.

Can anyone tell me how to do this in rails?

Basically:

raise e or some other cause
-> Log4r::MDC.put('subject', e.message)
continue with the exception

I found rescue_from but it just gives it to the handler and then stops.

Thanks a lot,

Christoph

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