PullMonkey Blog

Dynamic Select Boxes – Ruby on Rails 3

Over 4 years ago, I wrote a tutorial for doing dynamic (cascading) select boxes.
Still getting comments and emails to this day. Mostly asking how to get this working with rails 3, which has moved from prototype to jquery.
So here's a tutorial for getting 3 select boxes to trigger updates for each other.

First set things up:

I just used the html5 haml twitter bootstrap, etc template. Really useful.

If you need data, here's what I used - put this in your db/seeds.rb file:

Next, setup your model associations:

Genres have many artists.
Artists have many songs.
Genres have many songs through artists.

I'm just using a home controller to setup variables for the index page as well as setup variables for use in the dynamic updating:

Now the view just has the 3 select boxes and the unobtrusive javascript (triggered onchange) to make the ajax calls for updating:

We need our rjs files for updating the select boxes, one for the songs (when artist changes) and one for the artists and songs (when genre changes):

Our routes are simple:

That's it.

UPDATE: Here's an erb alternative for index.html.

And the js.haml can be converted to js.erb by taking #{...} and converting to <%= ... %> :

VIN API – Do you know about the complete data set?

Looking at our data trends for VIN API, we show about 15% of all requests are for the complete data set. It's the same price as the basic data set and rich with a ton of data.

Check out the data set from this post over 1 and half years ago. On top of the basic data set's year, make and model, the complete data set comes with data like MSRP, MPG (city and highway), dealer invoice, gas tank size, etc.

We get tons of hits for basic data, but at no additional charge we also provide the complete data set. Just add a complete
=> "true" to your request. So simple and there's no performance hit.

For more information, check out or examples and faq.

Enjoy!

Here's another look at the data elements from a comprehensive query:

Using Ruby to read from a MagTek USB Card Reader

Been playing around with a lot of USB devices lately, to get them to play nicely with some of our touch screen Rails apps.
One of the devices is a card reader - specifically a MagTek reader, and the same code works for the ELO reader.

I've tried a billion different ways to ensure we're reading in all the data. At first, I was just asking the usb stream to present me with a certain number of characters, b/c that's how all the examples do it.
But we're using a lot of different cards with the readers, so that didn't work too well. So now I just read one character at a time until we find the new line.
Here's the code to find the device, open it, close it and read from it, all whilst finding and converting the data as required.

So using this code, we take the swiped data and send it to our server for storage.

Using HTTPI with Curb to do multipart file uploads with spnego

It took a while to find a library that handled spnego requests, as opposed to shelling out to a curl --negotiate. Found httpi to work well with the curb adapter.
The problem was that the documentation didn't really explain how to do file uploads withing the httpi request block.
Wasn't too much of a big deal, but I thought it may save someone else some time.

Rubygem version incompatability with older Rails versions

We maintain a rails 2.3.8 application and haven't had to touch it in quite some time. But when we did, we came across this error:

uninitialized constant ActiveSupport::Dependencies::Mutex (NameError)

Then after applying the solution found here, we started getting this error:

undefined method `name' for "actionmailer":String (NoMethodError)

Both errors were resolved by using RVM to specify the rubygem version best suited for this application.

rvm rubygems 1.3.7

So our .rvmrc file now looks like this:

rvm use @
rvm rubygems 1.3.7

Headers and Footers in ruby’s Spreadsheet gem

Have you ever needed to add a header or footer to your spreadsheets in ruby?
Yah, well, we have 🙁
Yes, you can do this with the Write Excel gem.
But we've already written years worth of spreadsheet code with the spreadsheet gem and don't want to rewrite it all.

Anyway, we thought we'd share our little trick to get page headers using the spreadsheet gem.

So what you see here (above) goes into a config/initializer, something like RAILS_ROOT/config/initializer/enable_headers_in_spreadsheet_gem.rb. Here's what's going on:

1) We know that the write_from_scratch method is called when everything is said and done and the data is ready to be written to the spreadsheet file. So we make use of this and alias that method to write_from_scratch_without_header. Which opens us up to call our write_header method inside our write_from_scratch method which, of course, will call the original write_from_scratch method.

2) Our write_header method makes use of the already existing opcode for Header in the spreadsheet gem. It's not being used, so my guess is the developers intend on solving this issue at some point. We have to send the opcode, the length info and the string we want to write out. This was the trickiest part to figure out.

3) We expose an add_header method that simply takes a string and stores it in the header accessor. This means, to set the header, you simply say sheet.add_header("foo header").

To implement the footer, you'd just do the same thing, create a footer accessor, add a method to update it. Then build the writer_footer method with opcode(:footer) and append write_footer at the end of write_from_scratch.

Well, that took us some time to figure out, so enjoy and let me know if you have any questions.

Ruby’s stacked conditionals – who knew?

puts "hello readers" if you_are_a_reader if you_can_read unless you_already_read_it

I was playing around with some project euler code I'm working on (anyone else figure out the Pencils of Rays with code that executes in less than a minute??). Anyway - I was going through my code and adding "if debug" to the end of all my puts statements b/c I didn't want to see them for the next run through. So by mistake, I blindly added "if debug" at the end of 'puts "odd" if odd', giving me 'puts "odd" if odd if debug'. Neat. Then, going through trying to find the bottlenecks, I noticed it. So jumped into irb to make sure it was legit and it was.

Interesting. Not sure where I'd ever use it, though.

Hello Android – Pindah (with Mirah) Application

Did you install the Android SDK / JDK, etc?  If not, start here - http://developer.android.com/sdk/index.html.
If you're running 64-bit like me, make sure to install the ia32-libs, since the SDK is 32-bit.

This is completely based on the Hello Android tutorial - I didn't really do a whole lot, but the hope is that this will help get some more ruby devs into android development with a simple how-to.

Step 1 - Setup RVM with jruby

Note: RVM is awesome, if you don't use it or don't know about it - read more here.

rvm install jruby
cd /path/to/your/android/pindah/mirah/project/dir/
# using your .rvmrc will trigger `rvm use jruby` when you cd into your project dir.
echo "rvm use jruby" > .rvmrc
# this will make sure your .rvmrc is working, you should then be able 
# to use rvm info and see jruby
cd .

Step 2 - Install the mirah and pindah gems

# too easy
gem install mirah pindah

Step 3 - Create your first pindah app

pindah create com.example.android.hello_world
cd hello_world

Step 4 - Create your activity - HelloAndroid.mirah

# from your project dir and inside your pindah app dir 
<editor> src/com/example/android/hello_world/HelloWorld.mirah

This is the code I used:

Step 5 - Setup your AndroidManifest.xml file

This is where you define your app, version, name, etc, but more importantly for this example - what activity will handle your main intent.
Mine looks like this:

Step 6 - Install to your device

# make sure a device is recognized  ... 
# and make sure adb is in your path (platform-tools in the SDK)
adb devices
rake install

Playing with Mirah

Mirah (formally duby) is pretty freaking cool.   Plans are to scrap java and use mirah for future android development, we'll see.  Here's a rough example of some pretty basic mirah.

To get started, you'll need jruby and the mirah gem:

rvm install jruby
rvm use jruby (or put in your .rvmrc)
gem install mirah

Then create an example:

puts "hello world!!"
500.times do |x|
  puts x
end

Time in ruby:

time ruby test.mirah

...
=> .457s

Compile to Java and time:

mirahc test.mirah
time java Test

....
=> .081s

Less than 1/5 the time and it compiles to Java ... neat 🙂

mirahc -j test.mirah

// Generated from test.mirah
public class Test extends java.lang.Object {
  public static void main(java.lang.String[] argv) {
    int __xform_tmp_1 = 0;
    int __xform_tmp_2 = 0;
    int x = 0;
    java.io.PrintStream temp$1 = java.lang.System.out;
    temp$1.println("hello world");
    __xform_tmp_1 = 0;
    __xform_tmp_2 = 500;
    label2:
    while ((__xform_tmp_1 < __xform_tmp_2)) {
      x = __xform_tmp_1;
      label3:
       {
        java.io.PrintStream temp$4 = java.lang.System.out;
        temp$4.println(x);
      }
      __xform_tmp_1 = (__xform_tmp_1 + 1);
    }
  }
}

Using ruby to consolidate a list of numbers by shortening with hyphens

Check it out -