Paul Barry

Why Rails 3 Will Require Ruby 1.8.7

September 14, 2009

This past weekend I attended the Windy City Rails conference. It was in a great location in the heart of downtown Chicago and seemed to have a pretty good turn out. There were many great talks but this blog post will be focusing on a specific talk, and more precisely, part of a talk. Yehuda Katz gave a talk on the status of Rails 3. One of the things that he mentioned, which you may have already heard, is that Rails 3 will require Ruby 1.8.7 or higher, dropping support for Ruby 1.8.6. He also mentioned why they are doing this and I found the reason to be interesting. It’s not that the Rails core team wants to try to take advantage of any specific new features, it’s that Ruby 1.8.6 has a bug which has been fixed in 1.8.7.

To see the bug in action, I recommend that you install Ruby Version Manager (rvm). Once you have installed rvm, install Ruby 1.8.6 and Ruby 1.8.7.

The bug is that in Ruby 1.8.6, the hash method for Hash doesn’t generate the same hash code for different hashes with the same values:

$ rvm use 1.8.6
$ irb
ruby-1.8.6-p383 > {:x => 1}.hash
 => 1313270 
ruby-1.8.6-p383 > {:x => 1}.hash
 => 1307060 
ruby-1.8.6-p383 > {:x => 1}.hash
 => 1296440 
ruby-1.8.6-p383 > {:x => 1} == {:x => 1}
 => true
ruby-1.8.6-p383 > h = {{:x => 1} => "foo"}
 => {{:x=>1}=>"foo"} 
ruby-1.8.6-p383 > h[{:x => 1}]
 => nil

So despite the fact that two hashes have the same values and are equal, you can’t use a hash as a key in a hash, because that depends on the hash codes of the values being equal, which they aren’t. This is fixed in Ruby 1.8.7:

$ rvm use 1.8.7
$ irb
ruby-1.8.7-p174 > {:x => 1}.hash
 => 327875 
ruby-1.8.7-p174 > {:x => 1}.hash
 => 327875 
ruby-1.8.7-p174 > {:x => 1}.hash
 => 327875 
ruby-1.8.7-p174 > {:x => 1} == {:x => 1}
 => true 
ruby-1.8.7-p174 > h = {{:x => 1} => "foo"}
 => {{:x=>1}=>"foo"} 
ruby-1.8.7-p174 > h[{:x => 1}]
 => "foo" 

This is important because you could use a hash cache calls to a method that expects a hash, but only if you can use a hash as the key. This is one of the main reasons Rails 3 is going to require 1.8.7. They could make it worth for both 1.8.6 and 1.8.7 and higher, but why? It simplifies things to just require that you upgrade to Ruby 1.8.7 to use Rails 3. If you are using 1.8.6, this is probably a gotcha that you should be aware of.

Posted in Technology | Topics Ruby, Rails

Active Record Random

August 30, 2009

Are you looking for a way to select a random record that plays nice with named scope in your Rails app? Throw this into config/initializers/active_record_random.rb:

class ActiveRecord::Base
  def self.random
    if (c = count) > 0
      first(:offset => rand(c)) 
    end
  end
end

Now you can call random the same way you would call first or all. That means you can do Widget.random to get a random widget or Widget.fancy.random, to get a random fancy widget, assuming you have defined the fancy named scope for Widget.

Zip Code Proximity Search with Rails

June 27, 2009

So you’re building the next big social networking website using Rails and like all the other hip kids you are going to need to allow your users to search for other users near them. The fancy term for this is “Proximity Search”. For our search, we just want be able to find other people that are generally within some radius, like 5, 10 or 25 miles. For this, there is no need to geocode the address for each user in our database, we’ll just use their zip code. So effectively, in our system, every user’s location is just the center point of their zip code.

For starters we want to create a zip code model:

script/generate model zip code:string city:string state:string lat:decimal lon:decimal

That will create a model and a migration. You need to alter the migration to specify the precision and scale for the lat and the lon.

t.decimal :lat, :precision => 15, :scale => 10
t.decimal :lon, :precision => 15, :scale => 10

So to populate this database, luckily the good people over at the US Census Bureau have the data readily available for us. I’ve created a rake task to download and load that data into your zips table. Simply put the load.rake file from this gist into the lib/tasks directory of your Rails app.

So now when you run rake load:zip_codes you should see something like:

== Loaded 29470 zip codes in ( 1m 40s) ========================================

Next we need a table for our users. So let’s generate a model and a migration:

script/generate model user

I’ll save you the hassle of typing out all the fields at the command-line and just give them to you here. Paste this into the create_users migration that was generated:

t.string   :username
t.string   :email
t.string   :password
t.string   :password_confirmation
t.string   :first_name
t.string   :last_name
t.string   :address
t.string   :city
t.string   :state
t.integer  :zip_id    

Next you need to hook up the relationship between the zip and the user. This is basic stuff, the zip has many users and the user belongs to a zip.

Now we need some users to play with. A great tool for this is Mike Subelsky’s Random Data gem. I’ve already created a rake task that uses this gem to create some test user accounts. You call it like this:

rake load:random_users[10000]

The 10000 is the number of users we want the rake task to generate for us. Did you know you can pass command-line arguments to a rake task like that? Pretty spiffy. 10000 is a pretty good number because it gives us a fairly large dataset to work with and is still able to load in a reasonable amount of time. 10000 users finished in about 6 minutes and 30 seconds for me.

Next we need to setup our methods to do the querying. For this I basically used Josh Huckabee’s Simple Zip Code Perimeter Search method, but re-worked it a little so we can use named scope with it. You can grab the code for both zip.rb and user.rb from the gist.

There are a couple of things we get here. First is a named scope to easily find zip codes. Looking at the output of the loading of the random users, the last one for me was Mr. Steven Moore of Koloa, HI, 96756. So let’s see how many other people are in that zip code. Start up script/console and run this:

>> Zip.code(96756).users.count
=> 1

Hmm…I guess it’s lonely in Hawaii. Let’s find the zip code that randomly ended up with the most inhabitants:

>> Zip.count_by_sql "select zip_id, count(*) as count 
from users group by zip_id order by count desc limit 1"
=> 18177

Ok, so that’s the id of the zip record, not to be confused with the actual zip code. So let’s find the first person in this zip code:

>> user = Zip.find(18177).users.first
=> #<User id: 1267, username: "cabel1266", ...>

I got Ms. Cheryl Abel of Bloomville, NY. So now for the big moment. What we really want to do is find everyone within 25 miles of Cheryl.

>> user.within_miles(25).count(:all)
49

Looks like Cheryl has 49 people nearby. Let’s see who they are:

>> user.within_miles(25).all.each{|u|
?> puts "%.2f %20s, %2s, %5s" %
?> [u.distance, u.city, u.state, u.zip.code]}
0.00           Bloomville, NY, 13739
0.00           Bloomville, NY, 13739
0.00           Bloomville, NY, 13739
0.00           Bloomville, NY, 13739
0.00           Bloomville, NY, 13739
7.04            Worcester, NY, 12197
7.04            Worcester, NY, 12197
7.43             Maryland, NY, 12116
8.09             Meredith, NY, 13753
8.54            De Lancey, NY, 13752
8.71     Livingston Manor, NY, 12758
9.11             Roseboom, NY, 13450
9.88          Jordanville, NY, 13361
...

So there you have it! I’m still trying to work out some kinks with this and get it to work with count and will paginate, so if you have any suggestions, fork the gist, hack away and leave a comment. I’ll update this post when I get count and pagination working.

Posted in Technology | Topics Ruby, Rails | 2 Comments

The Busy Rails Developer's Intro To Rake

April 20, 2009

This is just a quick 60 second intro to Rake. If you are doing development with Ruby on Rails, you undoubtedly use Rake on a daily basis. For example, you use rake db:migrate to run your migrations or rake test:units to run your unit tests. But do you know how to write your own Rake tasks? If you never have done that, you might hesitate to write a rake task instead thinking you ran just write a quick ruby script rather than take the time to figure out how to write a Rake task.

So to create a rake task, in an existing Rails app, create a file called lib/tasks/app.rake. You can name it whatever you want as long as it ends in .rake. I’m choosing to use app because we are going to write some app-specific tasks. In the file, put this:

task :hello_world

Now from the command line you can run your task with rake hello_world. Nothing happens, but it runs. Now let’s have it print hello world:

task :hello_world do
  puts "Hello, World!"
end

Now when you run your task, it prints “Hello, World!”. Let’s add a description to our task to let people know what it does:

desc "Prints 'Hello, World!'"
task :hello_world do
  puts "Hello, World!"
end

Now if you run rake -T, you will see your hello_world task in the list of tasks. rake -T only shows tasks that have a description. You can also run rake -D hello_world to see the full description of the task. You should give all of your tasks that you expect users to run from the command-line a description.

Now a problem with our task is what happens if someone else wants to write a task named hello_world? Well, we would have a namespace problem. So what we want to do is put all of our tasks into the app namespace:

namespace :app do
  desc "Prints 'Hello, World!'"
  task :hello_world do
    puts "Hello, World!"
  end
end

So now we can run our task as rake app:hello_world.

So this is obviously not a real task. Let’s say we want to know what the load path of our app looks like. Easy, we’ll just do this:

namespace :app do
  desc "Prints load path of this app"
  task :load_paths do
    Rails.configuration.load_paths.each do |p|
      puts p
    end
  end
end

When you try to run this rake tast, you will get this error:

rake aborted!
uninitialized class variable @@configuration in Rails

The problem is that by default, a rake task doesn’t load the Rails environment. It’s easy to tell it to do that with this:

namespace :app do
  desc "Prints load path of this app"
  task :load_paths => :environment do
    Rails.configuration.load_paths.each do |p|
      puts p
    end
  end
end

By saying :load_path => :environment, you are saying that the load_path task depends on the environment being loaded. Or more specifically, you are saying “run the environment task before running this task”. There is a task called “environment”, and it loads the Rails environment. You won’t see it under rake -T, because it has no description because it is not a task you should run directly, only as a dependency of other tasks.

Now that we have the Rails environment loading, when you run the rake task, you will get the output you expect. If you make your task depend on environment, you will also be able to access your models from within your task. Now that you know the basics of Rake, you can easily get going making Rake tasks for your Rails app.

Posted in Technology | Topics Ruby, Rails, Rake | 8 Comments