Flowdock

Notes posted to Ruby on Rails

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March 27, 2009 - (>= v2.1.0)
1 thank

Gotcha with method calls inside select loop

Keep in mind that any methods you call on the object in the select loop will be strung together when the Javascript is rendered. For example:

page.select(".shipping_type_fee").each do |td|
  td.down("span").update("--").show
  td.down("img").hide
end

will be rendered as:

$$('.shipping_type_fee').each(function(value, index) {
  value.down("span").update("--").show().down("img").hide();
});

This is probably not what you want!

March 26, 2009 - (v2.0.0 - v2.3.2)
1 thank
March 25, 2009 - (>= v2.2.1)
1 thank

usage helper with block

helper example

def my_helper(&block)
  inner = capture(&block)
  out = "<somehtml>#{inner}</somehtml>"
  block_called_from_erb?(block) ? concat(out) : out
end

view example

<% my_helper do %>
  sometext
<% end %>

output

<somehtml>sometext</somehtml>

using ActionView::Helpers::CaptureHelper#capture

March 25, 2009 - (>= v2.2.1)
1 thank

alternative

not sure but block_called_from_erb? seems to be the replacement

March 24, 2009 - (>= v2.3.2)
2 thanks

if you get NameError: uninitialized constant ActionController::Caching::Sweeper

I got hit with this on an upgrade. Had a reference to ApplicationController::Base in development.rb (prod as well) which caused this problem http://rails.lighthouseapp.com/projects/8994/tickets/1977

Fix was to remove the loading of ApplicationController::Base and put it in an initializer (where it should have been).

March 24, 2009
2 thanks

Content_tag in helpers

Content_tag works great in a helper and is a nice way to clean up your views.

If you’re returning more than one content_tag you’ll need to concat them:

@content = content_tag(:tr, "first item")
@content << content_tag(:tr, "second item")

Be mindful that when doing the above, you must use parentheses around the content_tag options. In the above example, content_tag :tr, “second item” will return an error.

March 24, 2009
0 thanks

Finding all records WITHOUT associations

(Thanks to someone on the rails IRC channel who gave me this tip.)

Where Users and Events have a habtm relationship, to find all Users that have no events:

User.find(:all, :include => :events, :conditions => { "events_users.event_id" => nil})

(Note that when specifying a condition on a joined table, you have to put the field name in a string rather than a symbol. In the above example, :events_users.event_id will not work.)

March 24, 2009
1 thank

New and improved version

As this method is now deprecated, check the documentation for the new version (adds some more options), which gets included via a module:

ActiveRecord::Serialization#to_xml

March 23, 2009 - (v2.3.2)
4 thanks

So, how do you enable db sessions?

First, run:

rake db:sessions:create

Then, run your pending migrations. This will create the migration you need to run in order to create the sessions table.

Second, go into config/environment.rb and uncomment or put in:

config.action_controller.session_store = :active_record_store
config.action_controller.session = {
   :session_key => '_your_session_name_here',
   :secret      => 'SOME_CRYPTOGRAPHICALLY_SECURE_KEY'
 }

Third, get yourself a secure key with:

rake secret

And finally, paste your new key into the :secret above.

March 21, 2009
1 thank

Generating empty conditions

In some cases, you might find it useful for your lamba to generate empty conditions based on the passed parameter.

Class Article << ActiveRecord::Base

named_scope :category, lambda { |cat|
  if cat == :all
    { :conditions => {} }
  else
    { :conditions => { :category_id => cat } }
  end  
}

end

Allows you to call something like this:

categories = user_is_admin ? :all : @current_category
Article.category(categories)

Mostly useful when chaining named_scopes together. Avoids more complicated if statements.

March 21, 2009
4 thanks

Passing optional arguments with defaults to a named_scope

An easy way to do this. (This also shows how you can use joins in a named_scope as well.)

Class User << ActiveRecord::Base
belongs_to :semester 

named_scope :year, lambda { |*year|
  if year.empty? || year.first.nil?
    { :joins => :semester, :conditions => ["year = #{CURRENT_SEMESTER}"]}
  else
    { :joins => :semester, :conditions => ["year = #{year}"]}
  end
  }

end

You can then call:

User.year     # defaults to CURRENT_SEMESTER constant
User.year()  # same as above
User.year(nil)  # same as above; useful if passing a param value that may or may not exist, ie, param[:year]
User.year(2010)
March 21, 2009
0 thanks

Remember, named_scope returns an array

named_scope always returns a named_scope object, that acts like an array, even if you’re using it to only find one record. So if you’re trying to perform an association on the results of a named_scope, use the first method to return the model object and not the named_scope object.

Ie:

user = User.my_name_scope
user.articles   # assuming User has_many Articles

will return an error. use this instead:

user = User.my_named_scope.first
user.articles

(Of course this is a poor example because what you should be doing is performing the named_scope on Article with user as the condition, instead of on User. But if you do need to use the results of a named_scope to perform an association call, you have to do it this way to avoid an error.)

March 21, 2009
7 thanks

Use helpers in your ActionMailer views

It’s very easy to give your mailer access to helpers:

# Let your mailer user the ApplicationHelper methods
class MyMailer < ActionMailer::Base
  helper :application
end
March 20, 2009 - (>= v2.0.0)
9 thanks

Use the current URL, with changes

You can use the current URL, whatever it is, with changes, as in:

# Create a link to the current page in RSS form
url_for(:overwrite_params => {:format => :rss})

This can be super-helpful because it preserves any GET params (like search parameters)

March 20, 2009
2 thanks

Broadened Flash helper

Building on the below excellent example, you can create something with default options for how long it’s displayed and how long the fade is, and highlight:

def show_flash(options={})
  options = {:fade => 3, :display => 3, :highlight => true}.merge(options)
  html = content_tag(:div, flash.collect{ |key,msg| content_tag(:div, msg, :class => key, :attributes => "style = display: none;") }, :id => 'flash-message')
  html << content_tag(:script, "new Effect.Highlight('flash-message');") if options[:highlight]
  html << content_tag(:script, "$('flash-message').appear();")
  html << content_tag(:script, "setTimeout(\"$('flash-message').fade({duration: #{options[:fade]}});\", #{options[:display]*1000});")
end
March 20, 2009 - (v2.2.1)
0 thanks
March 20, 2009 - (>= v2.3.2)
1 thank
March 20, 2009 - (>= v2.3.2)
0 thanks

Nested Model Forms

For a good example of nested model forms check out the rails blog.

http://weblog.rubyonrails.org/2009/1/26/nested-model-forms

March 19, 2009
2 thanks

Expression

You can put some expression too. For example for I18n (using haml on view):

# some_locale.yml

links:
  contacts: "My contacts"

# index.html.haml

= link_to "#{t "links.contacts"}", :action => 'contacts'
March 18, 2009
2 thanks

:format

Just wanted to point out that you can also use the :format option:

url_for :controller=>'posts', :action=>'index', :format=>:xml

Results in:

"http://www.example.com/posts.xml"
March 17, 2009
0 thanks

Post =form post, NOT the http POST method

Post =forum post, NOT the http POST method

Note: any “Post” on this page has nothing to do with http methods. When I just looked at the collection_select code I was thrown off.

March 12, 2009
3 thanks
March 12, 2009
12 thanks

User a block to extend your associations

You can use blocks to extend your associations with extra methods.

code sample

has_many :children, :dependent => :destroy do
  def at(time)
    proxy_owner.children.find_with_deleted :all, :conditions => [
      "created_at <= :time AND (deleted_at > :time OR deleted_at IS NULL)", { :time => time }
    ]        
  end      
end

Model.children.each # do stuff
Model.children.at( 1.week.ago ).each # do old stuff

you must use ‘proxy_owner’ to link back to your model.

March 12, 2009 - (<= v2.1.0)
0 thanks

Another fix

Another way around this problem, with code that already employs String.first, is to change the ActiveSupport definition as follows (in environment.rb)

module ActiveSupport
  module CoreExtensions 
    module String 
      module Access
        def first(limit = 1)
          chars.to_a[0..(limit - 1)].to_s
        end
      end
    end
  end
end
March 12, 2009
2 thanks

Incompatible with Ruby 1.8.7

If using Rails < 2.2 with Ruby 1.8.7, calling truncate will result in the following error:

undefined method `length' for #<Enumerable::Enumerator:0xb74f952c>

The workaround (other than upgrading to Rails 2.2 or higher), is to overwrite the truncate method, by inserting the following at the end of environment.rb (or where it will be called on startup):

module ActionView
  module Helpers
    module TextHelper
      def truncate(text, length = 30, truncate_string = "...")
        if text.nil? then return end
        l = length - truncate_string.chars.to_a.size
        (text.chars.to_a.size > length ? text.chars.to_a[0...l].join + truncate_string : text).to_s
      end
    end
  end
end
March 12, 2009
0 thanks

PS

That didn’t render properly. Use:

String[1..1]

instead of

String.first
March 12, 2009
1 thank

Selected parameter

batasrki’s note on “selected” parameter is only true for cases which “value_method” returns an int also.

The strictly correct requirement for it to work is:

object.value_method == selected

(“object” is the current object on the iteration over collection)

Since the params hash returns Strings, using it against a value_method with return type of int will never give a valid match (thus no auto-selection is done), i.e., “13” != 13.

When you’ll be using other types of value_method, like String, there’s no need to append “.to_i”, e.g:

options_from_collection_for_select(@posts, "slug", "title", params[:slug])

where “slug” is a String, it will work as expected (current selected post is auto-selected by default).

March 11, 2009
2 thanks

Use table_exists? in initializers

When using ActiveRecords in initializers, eg. for creating small constant data on startup, use table_exists? for those statements.

the initalizers are also called for migrations, etc, and if you are installing a new instance of the project these initializers will fail the migration to create those tables in the first place.

March 11, 2009 - (>= v2.1.0)
2 thanks

Can also be used to conditionally apply filters

For example:

# Skip login filter if the request is for CSS
before_filter :require_login, :unless => lambda { |controller| controller.request.format.css? }

Calling request.format on the controller returns a Mime::Type object, which can then be queried for mime types, other examples:

controller.request.format.html?
controller.request.format.json?