Rails Time

Earlier in the month I was experiencing some odd behaviour in ruby.

irb(main):002:0> DateTime.now
=> Mon, 13 Aug 2012 17:04:34 +0100
irb(main):003:0> DateTime.now + 2.days
=> Sat, 22 Sep 2485 17:04:42 +0100

DateTime is a class with a limit that goes up to year 9999 and as far as I can tell isn't stored as seconds, the more commonly used Time class is measured in seconds and goes up to 03:14:08 UTC on 19 January 2038 on 32 bit (thanks Wikipedia). All the Railsy time goodies (example, 5.weeks.from_now) are measured in seconds too, and so are only compatible with Time (or Date) class but not DateTime.

It is almost misleading that ActiveRecord says time is stored as DateTime in databases, it is actually stored as Time.


References
DateTime
http://www.ruby-doc.org/stdlib-1.9.3/libdoc/date/rdoc/DateTime.html

Date
http://www.ruby-doc.org/stdlib-1.9.3/libdoc/date/rdoc/Date.html

Time in Core
http://ruby-doc.org/core-1.9.3/Time.html
Time in Date. The difference is this has to_date, to_time, and to_datetime methods.
http://www.ruby-doc.org/stdlib-1.9.3/libdoc/date/rdoc/Time.html

Story of Compiling Kernel for Linux VServer

So I've been having a fun week.

This is my first time compiling a kernel and It should be straight forward as there are some helpful websites available on just this topic:

pre-requisites:
Patience. This will take an hour (or more) on a decent quad core machine.
gcc-<version>-plugin-dev
fakeroot
make-kpkg
libncurses5-dev

On compiling the kernel with the VServer patch
http://linux-vserver.org/Installation_on_Linux_2.6
On compiling a general kernel
http://www.howtoforge.com/kernel_compilation_ubuntu
On using your complete kernel
http://www.centos.org/docs/2/rhl-cg-en-7.2/buildkernel-bootloader.html

I was running the commands on a Ubuntu12.04 virtualbox machine, following the Vserver instructions and while running make, it kept running out of disk space.
A quick google tells me the result should be about 500MB at most, and doesn't even tell you what the result should be. My attempts kept running out of space after about 40 minutes and after hitting 8GB used space, of which almost all the room was taken up by vmlinux (2.9GB) and vmlinux.o (4.9GB)
Apparently this is not normal.
Eventually after making a virtual hd with a size of 100GB (of which the result was just short of 9GB itself) it appeared to say a build of bzimage in /arch/boot/x86 folder was completed. This I could never find anywhere in the folder.

I am currently compiling using the howtoforge.com link so we will see how much success I shall have later on.
Currently I am getting GCC error "array subscript is above array bounds" quite a lot but it appears to be ignoring it.

#Edit
Its been 2 hours. I didn't set CONCURENCY_LEVEL= because of fear of it crashing. Starting to wonder if it was a mistake given how long this is taking. It is still compiling and it has just moved from ./drivers to ./fs. My favourite file list, sudo du --max-depth=1 -h | sort -rh , reports file is at 7.9GB and growing.


7.9G .
4.8G ./drivers
689M ./net
602M ./fs
316M ./arch
259M ./sound
126M ./kernel
76M ./security
58M ./crypto
41M ./mm
34M ./lib
31M ./include
19M ./Documentation
17M ./block
13M ./.tmp_versions
6.8M ./firmware
6.2M ./ipc
5.0M ./grsecurity
4.7M ./init
4.1M ./tools
3.8M ./scripts
2.8M ./virt
2.0M ./debian
156K ./samples
92K ./usr

Foolproof FactoryGirl Sequence

Turns out Sequencing in FactoryGirl isn't as easy as it used to be.
Factory.next has been deprecated and the two obvious ways to make a sequence now throw Trait error or Attribute already defined error "FactoryGirl::AttributeDefinitionError"

The problem with this first approach is name. In a normal sequence you would just say name but I want to use it in the description too. This somehow makes FactoryGirl believe name is a trait.

FactoryGirl.define do
  
  sequence(:code) {|n| "#{n+1000}"}
  
  factory :course do |u|
    name "CS#{ generate :code }"
    description "#{name}, 1st year, 1st semester, Foundation Of #{name}"
  end
end

This next example has a problem with the description line. This causes the description to generate 2 more names and throw an AttributeDefinitionError because you now have more than 1 name generated.
For some reason you cannot get around it by making the name line name = Factory.generate :name because name becomes a Trait again.

FactoryGirl.define do
  
  sequence(:name) {|n| "CS#{n+1000}"}
  
  factory :course do |u|
    name
    description "#{name}, 1st year, 1st semester, Foundation Of #{name}"
  end
end

This is the only thing that works. Static forcing FactoryGirl to use the already defined name again using the |a| block in description. It isn't as pretty as it could be but I have to live with it unless someone can tell me a better way. There is probably a solution where you use an after_build tag but that makes it longer and more complicated unnecessarily and it would still be ugly.

FactoryGirl.define do
  
  sequence(:name) {|n| "CS#{n+1000}"}
  
  factory :course do |u|
    u.name
    u.description {|a| "#{a.name}, 1st year, 1st semester, Foundation Of #{a.name}"}
  end
end

Importing a CSV File from Upload in Rails >= 3

For some reason I found the documentation for CSV's really bad!

What I wanted to do is accept a file from a form and parse it into a list of users to be added to the database without saving the CSV file. (Note: I DO save the file via the Paperclip Gem for logging purposes but I do all the processing from the file before it is saved to the database.)

When you have uploaded the file using Form_Tag, the file is usually in params[:name] where :name is tag you gave to file_field_tag :name
If you are using a Form_For, which by the way is strange if you do not intend to save it to the model in question, the file will be in params[:model][:name] from  f.file_field :name
The magic part is to actually get to the file you need to call .read on it.

In the View remember to make it multipart to accept files.


<%= form_for @model, :html => { :multipart => true } do |f| %>
  <%= f.label :file %><br />
  <%= f.file_field :file %><br /> 
  <%= f.submit "Upload" %>
<% end %>



In the Controller require csv, you do not need to install it as a gem but you do need to require it as it is in standard library not core.

require 'csv'
def my_method
@lines = []
CSV.parse(params[:submission][:file].read) do |row|
      @lines << row
end


Replace the yellow bits with whatever you want to do with your CSV file.
Have fun!

Cucumber Feature Fun

This post will be expanded later. For now its just a note to self.
http://lmarburger.github.com/2009/09/cucumber-features-in-subdirectories.html
http://robots.thoughtbot.com/post/189412598/five-ridiculously-awesome-cucumber-and-webrat
NOTE TO SELF:
Cucumber will not find step definitions when running a single feature unless you tell it to require the whole folder.

Good
cucumber --require folder_with_step_definitions feature_file_I_want_to_run
Real life Example:
cucumber -r features features/courses #whole folder
cucumber -r features features/courses/new_course.feature #Single Feature

Bad
cucumber feature_file_I_want_to_run
#Will hit a wall of Step Definition Missing messages.
cucumber -r /features /features/courses #Will cause it to start looking from Root and not Rails.root causing File Not Found issues

CSS Basics

I'm a shameless novice at CSS at the moment.
I'm just going through CSS at http://cssxcountry.codeschool.com and Just thought I'd take a second to note down some things that need noting in my head about CSS. This post therefore will be messy and perpetually unfinished. You were warned.

Targetting CSS:
<h1> is caught with h1 { someCSS; }
class="coffee" is caught with .coffee { someCSS; }
and,
id="tea" is caught with #tea

Compound CSS: multi-word classes or IDs
First, if class="some thing"
the CSS for it will NOT be .some thing, it will be .some.thing as it is like having class="some" and class="thing"
Note: I don't know if having multiple classes in the CSS is even allowable.

Text:
center is a possible option for text-align
bold, italic and similar are in font-style

Other:
CSS does not care if it has a space between an attribute and value.
float: right;
float:right;
Both are valid.

Elements in CSS are space separated, whereas classes or IDs are attached. li p.intro#first

ShorthandCSS fragments from http://www.dustindiaz.com/css-shorthand/
Font
element {
  font-style: normal;
  font-variant:normal;
  font-weight: normal;
  font-size: inherit;
  line-height: normal;
  font-family:inherit;
}
font shorthand oddity: http://www.impressivewebs.com/css-font-shorthand-property-cheat-sheet/
The style, variant and weight can be ommited and the line-height is seperated by the / character.

Margin
element {
  margin-top: number+unit;
  margin-right: number+unit;
  margin-bottom: number+unit;
  margin-left: number+unit;
}

CSS positioning and Stacking images in rails.

So you are using Ruby on Rails and you want a method of stacking images on top of each other.
Your answer will probably involve CSS but many of the blog posts and Q&A posts I found weren't too descriptive so here is my shot at explaining this from the perspective of someone who doesn't use CSS often.

First a short bit on parents in CSS

When using CSS, having one style inside the other makes the top level the parent. In this example the div with the id of "container" is the parent of the div with the id of "contained".

<div id="container">
<div id="contained">
</div>
</div>
This does not work with class instead of id.

<div class="container">
<div class="contained">
</div>
</div>

And the CSS position

There are several good resources explaining position and I will just link to my favourites.
http://www.barelyfitz.com/screencast/html-training/css/positioning/

http://css-tricks.com/absolute-positioning-inside-relative-positioning/

Onto the good stuff

Our CSS files are in assets/stylesheets/ and the one we are using is the application wide stylesheet application.css.scss

The technique is to have a position:relative parent container, so that all position:absolute items inside are in the same place against the relative container. Note that the container needs a size, it will not take the size of absolute children. My images are 64px*64px big so I have to force my container to be that large or the next HTML element in the flow will overlap it.
In application.css.scss

#container {
    position:relative;
    width: 64px;
    height: 64px;
}
#image {
    position: absolute;
    top: 0;
    left: 0;
}
This lets you place images with the id="image" inside a div of id="container". In my code I stack City.png vertically above Grass.png in the view. Note in versions of Rails before 3.1 you need to use :id => instead of the new syntax id:
<div id="container">
<%= image_tag("Grass.png", id:"image") %>
<%= image_tag("City.png", id:"image") %>
</div>