# Penalties of using an eval on every request **URL:** \ **Category:** Rails\ **Created:** [April 23, 2006, 8:43am UTC](https://www.ruby-forum.com/t/penalties-of-using-an-eval-on-every-request/58562 "2006-04-23T08:43:31Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![bluetrust](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/8e7dd6/32.png) [@bluetrust](https://www.ruby-forum.com/u/bluetrust)\ **Post date:** [April 23, 2006, 8:43am UTC](https://www.ruby-forum.com/t/penalties-of-using-an-eval-on-every-request/58562/1 "2006-04-23T08:43:31Z")
Hello RoR! I’m building a rails app for hosting multi-page surveys. I set up questionnaire, question, and question\_component models. Now I’m initializing them with some data. survey.rb q1 = Question.new “q1” q1.quote “Welcome to a test of the new interviewing system.” q2 = Question.new “q2” q2.quote “Do you like pie?” q2.single 1 =\> “Yes”, 2 =\> “No” q2.validation\_block = Proc.new { [1,2].include? @interview.answers[“2”] } questionnaire.questions.concat [q1, q2] – Real-life questionnaires can be thousands of questions long! How horrible would it be if I initialized the questionnaire.questions object, on each request, by reading survey.rb from disk and evaling it? Thanks for your time! - Mike ---
**Author:** ![bluetrust](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/8e7dd6/32.png) [@bluetrust](https://www.ruby-forum.com/u/bluetrust)\ **Post date:** [April 23, 2006, 9:52am UTC](https://www.ruby-forum.com/t/penalties-of-using-an-eval-on-every-request/58562/2 "2006-04-23T09:52:03Z")
> > > > > “Michael” == Michael J. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) writes: > – Real-life questionnaires can be thousands of questions long! > How horrible would it be if I initialized the questionnaire.questions > object, on each request, by reading survey.rb from disk and evaling it? ## Really horrible. Why don’t you store the populated questions in the database? ``` Calle D. http://www.livejournal.com/users/cdybedahl/ "Ah, optimism. I remember optimism." -- Anya, Buffy the Vampire ``` Slayer ---
**Author:** ![bluetrust](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/8e7dd6/32.png) [@bluetrust](https://www.ruby-forum.com/u/bluetrust)\ **Post date:** [April 24, 2006, 7:42pm UTC](https://www.ruby-forum.com/t/penalties-of-using-an-eval-on-every-request/58562/3 "2006-04-24T19:42:25Z")
Calle D. wrote: > > > > > > “Michael” == Michael J. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) writes: > > > – Real-life questionnaires can be thousands of questions long! > > > How horrible would it be if I initialized the questionnaire.questions > > object, on each request, by reading survey.rb from disk and evaling it? > > ## Really horrible. Why don’t you store the populated questions in the database? > > ``` > Calle D. > http://www.livejournal.com/users/cdybedahl/ > "Ah, optimism. I remember optimism." -- Anya, Buffy the Vampire > > ``` > > Slayer That’s a good question: why not initialize it once and then store the populated questions in the database? That’s what I was doing, and it worked just fine, until I added procedures (proc/lambda) for validation and branching code. Procs seem really useful under the problem at hand, but they make the questions unserializable. Here’s an example of some of the procs I use: q2.validation\_block = Proc.new { [1,2].include? @interview.answers[“q2”] } q2.after\_block = Proc.new do if @interview.answers[“q2”] == 1 @interview.skip “q3” else @interview.skip “q4” end end So in the controller it lets me do things like this: if current\_question.validates? current\_question.after\_block.call render …next question… else render …same question… end I feel like I’m being a moron and should stick the questionnaire data in a require, but that’s just for entire modules, right? ---
**Author:** ![bluetrust](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/8e7dd6/32.png) [@bluetrust](https://www.ruby-forum.com/u/bluetrust)\ **Post date:** [April 25, 2006, 10:26am UTC](https://www.ruby-forum.com/t/penalties-of-using-an-eval-on-every-request/58562/4 "2006-04-25T10:26:17Z")
> > > > > “Michael” == Michael J. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) writes: > That’s what I was doing, and it worked just fine, until I added > procedures (proc/lambda) for validation and branching code. Procs seem > really useful under the problem at hand, but they make the questions > unserializable. They also make your questions sound more like full-on model classes than as instances of the same model class. Have you considered making a general Question class and then subclasses of that for each variant of code you need? > I feel like I’m being a moron and should stick the questionnaire data in > a require, but that’s just for entire modules, right? ## It’s for including code, so I can’t see why you wouldn’t do it that way. If you can load all your questions once at startup, it should work fine. ``` Calle D. http://www.livejournal.com/users/cdybedahl/ "Last week was a nightmare, never to be repeated - until this week" -- Tom, a.s.r ``` ---
**Author:** ![bluetrust](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/8e7dd6/32.png) [@bluetrust](https://www.ruby-forum.com/u/bluetrust)\ **Post date:** [April 25, 2006, 3:06am UTC](https://www.ruby-forum.com/t/penalties-of-using-an-eval-on-every-request/58562/5 "2006-04-25T03:06:05Z")
Michael J. wrote: > Hello RoR! > > I’m building a rails app for hosting multi-page surveys. I set up > questionnaire, question, and question\_component models. Now I’m > initializing them with some data. > > survey.rb > q1 = Question.new “q1” > q1.quote “Welcome to a test of the new interviewing system.” > > q2 = Question.new “q2” > q2.quote “Do you like pie?” > q2.single 1 =\> “Yes”, 2 =\> “No” > q2.validation\_block = Proc.new { [1,2].include? > @interview.answers[“2”] } > > questionnaire.questions.concat [q1, q2] > > – Real-life questionnaires can be thousands of questions long! > > How horrible would it be if I initialized the questionnaire.questions > object, on each request, by reading survey.rb from disk and evaling it? Hello Michael, I’m also working on a “questionnaire” system. The solution I came up with is to store the definition of each question in a separate file (in the file system). In addition, you have a “map” file which defines the overall sequence of questions – each question being uniquely identified by its name for example. This way you only need to read in one question at a time – and in such a system each request usually relates to just one question. This avoids the overhead of reading the entire questionnaire definition for each request. After each request you can allow the question object to be discarded provided you have first saved the user’s answer data. All you need to preserve between requests is the “map” structure (which can be serialised) and the user response data (which can be serialised or put in a database record, etc). One reference I have found useful is SCORM (google for it). SCORM is a standardised way of looking at the architecture of online learning activities – and questionnaires are very similar. If you want to clean up your question definitions, this article about domain specific languages in Ruby is worth reading: [http://jamis.jamisbuck.org/articles/2006/04/20/writing-domain-specific-languages](http://jamis.jamisbuck.org/articles/2006/04/20/writing-domain-specific-languages) Paul Howson (Qld Australia)