Posts Tagged ‘ruby’

Is there any way to specify the RAILS_ENV when using Passenger? I tried setting it in my environment.rb, but it doesn’t seem to take anything other than “production” … setting the RAILS_ENV constant instead of the ENV[‘RAILS_ENV’] eventually did the trick.

For a way to set Rails_env differently depending on the capistrano stage being deployed to, see this post

When you’re debugging/analyzing MySQL queries in the Rails console, it helps to turn on ActiveRecord logging:

#Enable ActiveRecord logging
def loud_logger(enable = true)
  logger = (enable == true ? Logger.new(STDOUT) : nil)
  ActiveRecord::Base.logger = logger
  ActiveRecord::Base.clear_active_connections!
end

An excellent post on the various syntaxes for Ruby ‘case’ statements

collect {|item|block} and map{|item|block} do the same thing – return an array of things returned by the block.  This is different from returning specific items in the collection being iterated over.

Which leads to select.

select{|item|block} will return actual collection items being iterated over if, for each item, the block condition evaluates to true. Not the same as returning what the block, itself, may return.  In the case of select, the block would always return an instance of class TrueClass or FalseClass.  Typically, [true, false, ..., true] is not what you’re looking for in your resulting array.

Slightly modifying the core RDoc example:

a = ["a", "b", "c", "d"]      #=> ["a", "b", "c", "d"]
a.map {|item|"a" == item}     #=> [true, false, false, false]
a.select {|item|"a" == item}  #=> ["a"]

Assuming you want to make sure that no two models have the same COMBINATION of values for a and b:

so having two models with:

a = 1, b = 2
a = 1, b = 3

would not be a conflict.

If that’s the case then the standard validation

class Widget < ActiveRecord::Base
validates_uniqueness_of :a, :b
end

wouldn’t work since it tries to prevent saving two models with the same value of a, OR with the same value of b.

And even if that’s not what you’re trying to do, and you’re ok with the example being a conflict, validates_uniqueness_of doesn’t guarantee uniqueness if two users try to save conflicting records simultaneously.  The validation works by first trying to find a record with the value, and if it doesn’t find it inserting the ‘new’ record, and this can fail due to a concurrency hole.

To fill this hole requires leaning on the database server, and the way to do that in SQL is by having a unique index on the table which covers the column or columns you want to be unique. This assume you are using a database which supports it, e.g. MySql.

To create an index you can create a migration which includes a statement like

add_index  :widgets, [:a, :b], :unique => true)

Assuming that the table name for the model is ‘widgets’

Now if you do this, you also need to be aware that if you try to save a record with a uniqueness conflict the save will raise an ActiveRecord::StatementInvalid exception, which you’ll need to rescue and do something like telling the user of the conflict so that he can rectify it.

>> ActiveRecord::Base.connection.instance_variable_set :@logger, Logger.new(STDOUT)

I use the Rails console mainly to poke around in my database. Unfortunately the display of the records returned leaves a lot to be desired. Hirb solves this problem perfectly! Here are the quick steps you need to get the basic functionaliy:

1. Install the gem: sudo gem install cldwalker-hirb –source http://gems.github.com
2. Start the console: ruby script/console
3. Require Hirb: require ‘hirb’
4. Enable it: Hirb.enable
5. Try it: x = Model.find(:all)

1. Upgrade to latest version of RubyGems (‘sudo gem update –system’)
2. Add GitHub repository (‘gem sources -a http://gems.github.com’)
3. Upgrade to latest version of Ziya (‘sudo gem install derailed-ziya’)
4. Install Ziya in project directory (‘Ziyafy –charts’ in project home, note the double dash)
5. Add ziya.rb to config/initializers directory
6. Copy your themes into ../public/themes/

Some other thoughts: If you’re frustrated by the almost non-existent documentation and the fact that the gem is in constant flux, don’t despair. The best way to understand how to customize your graph is to look through the example themes (for some reason they didn’t install with my gem but I downloaded them from GitHub).

Note: You can not instantiate the Ziya object in the controller corresponding to the chart’s view. It needs to be in a separate controller. Otherwise, an XML file (instead of a chart) will be returned when that controller is invoked.

Also, the reference material at XML/SWF charts is very useful and Ziya seems to adhere quite closely to the naming conventions.

I also found that I needed user-defined functions fairly quickly to customize axes etc.

Here is an example of how to use Ziya to create a scatter chart:

== Chart Controller ==

01: def load_ef

02:    # Create graph data object
03:    chart_data   = Array.new

04:    # Pull portfolios out of database
05:   @query = sessions[:period].to_i

06:    @portfolios = Portfolio.find(:all, :conditions => [“period = ?”, @query])

07:    # Strip out risk and return
08:    @portfolios.each { |x|
09:       chart_data  << x.std_dev
10:       chart_data  << x.port_ret
11:    }

12:    title = “User-entered portfolios”

13:    chart = Ziya::Charts::Scatter.new(‘LICENSE-KEY’)
14:    chart.add( :axis_category_text, %w[x y]*(chart_data.length/2) )
15:    chart.add( :series, title, chart_data )

16:    chart.add( :theme , “assetcorrelation” )

17:    respond_to do |fmt|
18:      fmt.xml { render : xml => chart.to_xml }
19:    end
20: end

== View ==

1: <div>
2:   <%= ziya_chart load_ef_url, :size => “1200×800” – %>
3: </div>

== Routes.rb ==

1:  map.load_ef   ‘/chart/load_ef’,   :controller => ‘chart’, :action => ‘load_ef’

As far as I understand, Rails will first look for a method in your controller that matches the view, then, once it starts rendering the view, it hits the callback (line 2 in the view snippet above) and at that point calls the method in the chart_controller to render the chart data, using the routing information in Routes.rb.

Note that in this case, I am pulling the data for the chart out of my database.

Rails Guides

Keeping Ruby on Rails up to date:

Installing gems on Dreamhost

Rails > 2.1 now with gem dependencies and here

ruby -v — check which version of ruby you have installed

rails -v — check which version of rails you have installed

gem list — check versions of all installed gems

sudo gem update — bulk update of all installed gems (some say this is a bad idea)

sudo gem update –system (updates rubygems, note use of double dash)

sudo gem uninstall <gem_name> — uninstall a specific gem

sudo gem install <gem_name> — install a specific gem

sudo gem cleanup — remove old versions of gems

sudo gem install -v=2.0.2 rails — install a specific version of Rails (to stay in synch with Dreamhost)

Rmagick

Installing Rmagick

1. sudo apt-get update
2. sudo apt-get install imagemagick
3. Then, install the imagemagick9 dev library:
   sudo apt-get install libmagick9-dev
4. Last, install the RMagick gem:
sudo gem install rmagick

Rails Migrations

Useful cheat sheet

Use rake db:schema:load if having trouble with Rails migrations and you have a working schema.

Use rake db:migrate VERSION=3 to roll back to version 3

Use rake db:migrate:reset — drop db, recreate it, and then run all migrations

rake db:rollback — go back one migration

rake db:migrate:redo — undo last migration and then redo it

rake db:sessions:clear — purge sessions from database

MySQL

To create a new MySQL DB on Dreamhost it is best to use the Dreamhost panel.

To create a database locally: mysqladmin -u root -p create <dbname>_development

mysql -u yourdblogin -p -hyourdbdomain.yourdomain.com yourdb

To load a table into a database:

mysql -u [username] -p[password] -hmysql.[domainname].com [database_name] < iso_country_list.sql

drop table sessions; — delete the sessions table

show tables; — show all tables for database

describe sessions; — show the sessions table

check table sessions; — check the sessions table for corruption and/or nonexistence

Gem Sources

Make sure to add GitHub: gem sources -a http://gems.github.com

Unfortunately, the New Relic performance monitor for Ruby on Rails doesn’t work with mod_rails (Passenger). According to a support email from them it currently “only supports mongrel and thin (without sockets)”. They plan to support Passenger in the future. That’s great news because they provide an excellent performance monitoring tool which is very easy to install and use.

Update: New Relic has added support for mod_rails. I received this email from their excellent customer support:

I was just digging through my support emails and found a few people who had inquired about RPM supporting Phusion Passenger, aka mod_rails.

 

I wanted to let you know that we released a version of the agent with ‘beta’ support for Passenger.

 

If you’re interested, check it out and let us know how it works for you!

 

To try it out, just do:

 

script/install –force http://svn.newrelic.com/rpm/agent/newrelic_rpm

 

Bill Kayser

New Relic RPM Developer