# Stuck on silly nil issue **URL:** \ **Category:** ruby-talk\ **Created:** [25 August 2009 06:40 UTC](https://rubytalk.org/t/stuck-on-silly-nil-issue/55065 "2009-08-25T06:40:22Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![Nick\_Wild](https://avatars.discourse-cdn.com/v4/letter/n/c0e974/32.png) [@Nick\_Wild](https://rubytalk.org/u/Nick_Wild)\ **Post date:** [25 August 2009 06:40 UTC](https://rubytalk.org/t/stuck-on-silly-nil-issue/55065/1 "2009-08-25T06:40:22Z")
Banging my head on the desk over this.. I'll try to generalize my issue down to this scenario. Since I remember always using cars back in programming classes here it goes... cars["yugo"].status["available"] = 2 Some thing like this is working perfectly... if cars["yugo"].status["available"]    puts "There are" + cars["yugo"].status["available"].to\_i + "yugos available" end if cars["kia"].status["available"]    puts "There are" + cars["kia"].status["available"].to\_i + "kia available" end I get "There are 2 yugos available" But when I do this.... cars\_to\_scan = ["yugo", "kia"] cars\_to\_scan.each { |carbrand|   if cars[carbrand].status["available"]     puts cars["yugo"].status["available"].to\_i + carbrand + "available" } I hit: You have a nil object when you didn't expect it! You might have expected an instance of ActiveRecord::Base. The error occurred while evaluating nil.attributes So I tried if cars[carbrand.to\_s].status["available"] and also this: unless cars[carbrand.to\_s].status["available"].nil? same error I don't understand why I can use the string directly but when I try indirectly it's hitting this error and why I'm getting a nil error when I'm trying to use the if to check if the object is not nil. I'm still really baffled by certain things in ruby. Thanks in advance for any tips or pointers. I'm sorry for the newbie question but this is one of those dig through google and books and still come up ready to pull your hair out little niggling things. Thanks! > **路路路** > > -- > Posted via [http://www.ruby-forum.com/](http://www.ruby-forum.com/). ---
**Author:** ![Robert\_K1](https://yyz1.discourse-cdn.com/flex029/user_avatar/rubytalk.org/robert_k1/32/1830_2.png) [@Robert\_K1](https://rubytalk.org/u/Robert_K1)\ **Post date:** [25 August 2009 06:59 UTC](https://rubytalk.org/t/stuck-on-silly-nil-issue/55065/2 "2009-08-25T06:59:53Z")
Look at your line that starts with "puts" - it's just a silly copy and paste error. 馃檪 Note: if you need to access a single object multiple times in the block, it is more efficient and probably also more readable to just pull it once. Cheers robert > **路路路** > > 2009/8/25 Nick Wild \: > > > Banging my head on the desk over this.. > > > > I'll try to generalize my issue down to this scenario. Since I remember > > always using cars back in programming classes here it goes... > > > > cars["yugo"].status["available"] = 2 > > > > Some thing like this is working perfectly... > > > > if cars["yugo"].status["available"] > > puts "There are" + cars["yugo"].status["available"].to\_i + "yugos > > available" > > end > > if cars["kia"].status["available"] > > puts "There are" + cars["kia"].status["available"].to\_i + "kia > > available" > > end > > > > I get "There are 2 yugos available" > > > > But when I do this.... > > > > cars\_to\_scan = ["yugo", "kia"] > > cars\_to\_scan.each { |carbrand| > > if cars[carbrand].status["available"] > > puts cars["yugo"].status["available"].to\_i + carbrand + "available" > > } > > > > I hit: You have a nil object when you didn't expect it! > > You might have expected an instance of ActiveRecord::Base. > > The error occurred while evaluating nil.attributes > > > > So I tried > > > > if cars[carbrand.to\_s].status["available"] > > and also this: > > unless cars[carbrand.to\_s].status["available"].nil? > > > > same error > > > > I don't understand why I can use the string directly but when I try > > indirectly it's hitting this error and why I'm getting a nil error when > > I'm trying to use the if to check if the object is not nil. > > > > I'm still really baffled by certain things in ruby. Thanks in advance > > for any tips or pointers. I'm sorry for the newbie question but this is > > one of those dig through google and books and still come up ready to > > pull your hair out little niggling things. > > -- > remember.guy do |as, often| as.you\_can - without end > [http://blog.rubybestpractices.com/](http://blog.rubybestpractices.com/) ---
**Author:** ![Nick\_Wild](https://avatars.discourse-cdn.com/v4/letter/n/c0e974/32.png) [@Nick\_Wild](https://rubytalk.org/u/Nick_Wild)\ **Post date:** [25 August 2009 07:17 UTC](https://rubytalk.org/t/stuck-on-silly-nil-issue/55065/3 "2009-08-25T07:17:54Z")
Robert - Thanks for taking a look! Maybe I should have used my actual code instead of trying to write up an example. The lack of end on my if in the example wasn't the issue. Here's the actual block with content sanitized. Where xmldoc is a REXML object I'm using without problem elsewhere in this code. The IF line below is where I hit the problems types = ["foo", "bar", "stuff", "other", "favorite"] conditions = ["up", "down", "marginal"] types.each { |@scan\_type|   conditions.each { |@scan\_conditions|    if xmldoc.elements[@scan\_type].attributes[@scan\_conditions]     count\_to\_add = site.elements[@scan\_type].attributes[@scan\_conditions].to\_i     addtodb(siteToSave.id, scan\_type, scan\_conditions,count\_to\_add)    end   } } Robert Klemme wrote: > **路路路** > > > 2009/8/25 Nick Wild \: > > > > > same error > > > > > > I don't understand why I can use the string directly but when I try > > > indirectly it's hitting this error and why I'm getting a nil error when > > > I'm trying to use the if to check if the object is not nil. > > > > > > I'm still really baffled by certain things in ruby. Thanks in advance > > > for any tips or pointers. I'm sorry for the newbie question but this is > > > one of those dig through google and books and still come up ready to > > > pull your hair out little niggling things. > > > > Look at your line that starts with "puts" - it's just a silly copy and > > paste error. 馃檪 > > > > Note: if you need to access a single object multiple times in the > > block, it is more efficient and probably also more readable to just > > pull it once. > > > > Cheers > > > > robert > > -- > Posted via [http://www.ruby-forum.com/\](http://www.ruby-forum.com/%5C). ---
**Author:** ![Robert\_K1](https://yyz1.discourse-cdn.com/flex029/user_avatar/rubytalk.org/robert_k1/32/1830_2.png) [@Robert\_K1](https://rubytalk.org/u/Robert_K1)\ **Post date:** [25 August 2009 07:24 UTC](https://rubytalk.org/t/stuck-on-silly-nil-issue/55065/4 "2009-08-25T07:24:33Z")
Nick, please do not top post. > Robert - Thanks for taking a look! > > Maybe I should have used my actual code instead of trying to write up an > example. The lack of end on my if in the example wasn't the issue. I actually meant the use of a constant vs. the local variable from the iteration: puts cars["yugo"] ... > Here's the actual block with content sanitized. > > Where xmldoc is a REXML object I'm using without problem elsewhere in > this code. > > The IF line below is where I hit the problems > > types = ["foo", "bar", "stuff", "other", "favorite"] > conditions = ["up", "down", "marginal"] > > types.each { |@scan\_type| > conditions.each { |@scan\_conditions| > if xmldoc.elements[@scan\_type].attributes[@scan\_conditions] > count\_to\_add = > site.elements[@scan\_type].attributes[@scan\_conditions].to\_i > addtodb(siteToSave.id, scan\_type, scan\_conditions,count\_to\_add) > end > } > } You are abusing instance variables. Please get rid of all the @'s as they have no use in this case. Then, #elements returns a collection of elements - you need to iterate them if you want to get at each elements attributes. I believe though that there are XPath expressions which directly select attributes. I am unsure whether REXML supports them. See: [http://www.w3schools.com/xpath/](http://www.w3schools.com/xpath/) [http://www.zvon.org/xxl/XPathTutorial/General/examples.html](http://www.zvon.org/xxl/XPathTutorial/General/examples.html) My previous remark about not fetching things twice is even more valid with REXML. By refactoring to only fetch certain things once your code will become more readable and more efficient. Kind regards robert > **路路路** > > 2009/8/25 Nick Wild \: > > -- > remember.guy do |as, often| as.you\_can - without end > [http://blog.rubybestpractices.com/](http://blog.rubybestpractices.com/) ---
**Author:** ![Nick\_Wild](https://avatars.discourse-cdn.com/v4/letter/n/c0e974/32.png) [@Nick\_Wild](https://rubytalk.org/u/Nick_Wild)\ **Post date:** [25 August 2009 07:42 UTC](https://rubytalk.org/t/stuck-on-silly-nil-issue/55065/5 "2009-08-25T07:42:06Z")
Hopefully this will not top post. Yes, sorry my example was so hackish I was churning a bunch of code trying to zero in on the issue. I'll switch over to iterating through with a single fetch per pass and shed the ivars. For what it is worth I did just figure out that when I test if xmldoc.elements[@scan\_type] is nil first this code works albeit inefficiently as noted. I was foolishly thinking that nil.nil would eval as false for the if. Thank you again for your advice. Cheers, Nick > **路路路** > > -- > Posted via [http://www.ruby-forum.com/](http://www.ruby-forum.com/).