Code Golf: Saving Time

Aug 28, 2008  -  Comments

Here is my submission for the Saving Time challenge. Code size: 319 bytes (not the worst, but close).

11.times{|x|a<<[' ']*17}
a[b[m][0]][b[m][1]]=h==m ?'x':'m'
a.map{|x|puts x.join.rstrip}

Tagged: rubycode golf

Working with the flash hash

Aug 17, 2008  -  Comments

The flash hash is what Rails uses to display messages (both notices and errors). Since it's a Hash, you can assign any key/value pair that you want, but I tend to stick with flash[:notice] for a success message, and flash[:error] for an error message.

In my opinion, using the flash hash is a little confusing. I haven't come across a book or tutorial that fully explains how to control it properly. So, here are the options for using the flash hash in Rails.

flash[:key] and flash.now[:key]

The following method shows how to best use the flash hash:

def create
  @user = User.new(params[:user])
  respond_to do |format|
    if @user.save
      flash[:notice] = 'User was successfully created.'
      format.html { redirect_to admin_users_path }
      flash.now[:error] = 'The user could not be created'
      format.html { render :action => 'new' }
rescue Exception => ex
  logger.warn('ERROR: ' + ex.message)
  flash.now[:error] = 'There was an error creating the user.'
  render :action => 'new'

Notice that I use the flash hash in two different ways: flash[:key] and flash.now[:key]. The way I use it depends on when I want it displayed. The flash[:key] usage should only be used before redirection, because it makes the object available for the current action and the next action. The flash.now[:key] usage should be used when you only want the flash object to be available to the current action.

Here's an example why you shouldn't use flash[:key] without redirection. Let's say this is your controller:

class MainController < ApplicationController
  def index
    flash[:notice] = 'Welcome to the site!'
  def profile

When you visit the index page, you'll see the message 'Welcome to the site!.' If you then click a link from the index page that takes you to the profile page, you'll still see the message 'Welcome to the site!' because the flash[:key] is available to the current action and the next action.

Displaying the flash

Here is a really helpful method to display the contents of the flash hash that I modified from one of Ryan Bates' awesome Railscasts:

<%- flash.each do |key, msg| -%>
	<div id="<%= key %>">
		<p style="float:right;"><%= link_to_function 'X', "Effect.Fade('#{key}')" %></p>
		<p><%= msg %></p>
		<div class="clear"></div>
<%- end -%>

This method will loop through each key in your flash hash and create a div with the name of the key, then put the contents inside with a link to close the message div.

I put this method in a partial called _notice_div.html.erb and include it at the top of my application layout. Here are the styles I use for notices and errors:

#notice { background-color: #A4E7A0; border: 1px solid #26722D; }
#error { background-color: #F0A8A8; border: 1px solid #900; }
#notice, #error { width: 90%; margin: 0 auto 10px auto; padding: 5px; }
#notice p, #error p { margin-left: 20px; padding: 0; font-size: .75em; color: #000; }
#notice a, #error a { text-decoration: none; padding: 0 3px; }
#notice a { border: 1px solid #26722D; color: #26722D; }
#error a { border: 1px solid #900; color: #900; }
#notice a:hover, #error a:hover { color: #333; border: 1px solid #333; }

This is a notice div.

This is an error div.

Tagged: tutorialcssrailsflash

Routes Demystified

Aug 02, 2008  -  Comments

It took me a while to discover the full potential of Rails' routes. I slowly learned more and more neat stuff that made me like them more and more. They are extremely powerful and are very useful for URL re-writing. Following is all of my route knowledge. If you notice something that I didn't cover, please leave it in the comments.

A few basic routes:

# this will route domain.com/ to the index action of your main controller
map.connect '', :controller => 'main'

# this will create a custom URL for your about-us page
map.connect 'custom-url/about-us', :controller => 'about_us', :action => 'index'

Pay attention to the order of your routes in your routes.rb file. They are evaluated in order from top to bottom. Routes at the top will be used before routes at the bottom if they are too similar.

Named Routes

Instead of saying map.connect, let's get crazy and name our routes. I'll use the same routes as above and add a few.

# you can now call this route with home_path or home_url
map.home '', :controller => 'main'

# call this route with about_us_path or about_us_url
map.about_us 'custom-url/about-us', :controller => 'about_us', :action => 'index'

# symbols in the routes define options you pass when calling the route
# call product_details_path(:id => @product) to access this route
map.product_details 'products/detail-view/:id', :controller => 'products', :action => 'show'
# all-purpose route for the products controller : products_path(:action => 'search') or products_path(:action => 'buy', :id => product)
map.products 'products/:action/:id', :controller => 'products'

Route Blocks Using with_options

If we have several routes for the same controller, it makes sense to use with_options to simplify the definitions.

map.with_options :controller => 'news' do |m|
  m.news 'news-releases/list', :action => 'index' # news_path
  m.news_details 'news-releases/details/:id', :action => 'show' # news_details_path(:id => news_release)
  m.news_author 'news-releases/by-author/:name', :action => 'author' # news_author_path(:name => 'Bill')

Better URLs with Routes

Routes are great for creating search engine friendly URLs. Supposed you'd like to add the title of your blog post to the URL.

map.blog_details 'blog/details/:id/:title', :controller => 'blog', :action => 'show', :title => nil

Now you can call the blog_details path and give it the :id and :title as options for the URL. Also notice that I set :title => nil at the end of the route. This marks that option as optional for the route call.

# this call will generate the following URL: http://domain.com/blog/details/1/My-First-Blog-Post
# I'm using a helper method in this call entitled 'strip_chars', it is below
blog_details_path(:id => post, :title => strip_chars(post.title)) %>

# you can also omit the title when invoking the route because it is optional.
# since your 'details' method will be using the :id parameter to find the record
# we don't really need the title, it's just for search engines
blog_details_path(:id => post) %>

# this helper method takes a string, replaces all spaces with dashes, then strips out all non-letter, non-number, non-dashes
# it's good for generating URL-friendly titles
def strip_chars(string='')
  return '' if string.blank?
  string.gsub(' ','-').gsub(/[^a-z0-9\-]+/i, '')

Caching and Pagination

If we cache our site, and certain actions show a paginated list, then we need to add the :page attribute to the route to ensure that the cache is recorded properly. After all, to our server /blog/list looks the exact same as /blog/list?page=2 when retrieving cached pages.

map.blog 'blog/list/:page',
         :controller => 'blog',
         :action => 'list',
         :requirements => {:page => /\d+/},
         :page => nil
# blog_path
# blog_path(:page => 1)

Notice that we added something new, the :requirements option. For :page, it's a regular expression telling us the supplied value must be a number. I've also set :page => nil so that we don't always have to specify it when invoking the route.

One thing to watch out for when calling a paged route is to be careful when you're on another paged section of your site. Say I have the route above for blogs and a similar route for news releases. If I'm on the page /news/list/5 and I call blog_path it will take the :page parameter from the current URL and you'll end up on page 5 of your blog post list. Confused? Just make sure when you are calling a paged route to specify it as blog_path(:page => 1) to explicitly go to /blog/list/1 or call blog_path(:page => nil) to go to /blog/list. Both will work.

Route Conditions

Similar to RESTful routes, you can specify the method of the request with the :requirements option. While this is useful, it makes much more sense to just use map.resources to get real RESTful routes.

map.connect 'blog-post/:id', :controller => 'blog', :action => 'show', :requirements => { :method => :get }
map.connect 'blog-post/:id', :controller => 'blog', :action => 'update', :requirements => { :method => :post }

# a GET method to /blog-post/1 will route to the 'show' action
# a POST method to /blog-post/1 will route to the 'update' action

I think that's enough for normal routes. Hopefully soon I can write a post on RESTful routes, which are a whole different beast.

Tagged: tutorialrailsroutes

Rails Tips

Jul 13, 2008  -  Comments

While there are no shortages of posts listing tips for Rails, or lesser-known Ruby methods, I decided to write this post because these are shortcuts or helpers that I didn't know about until fairly recently. I'm going to try and update this post as I discover new railties and rubyisms along the way, so check back every now and then.


This is really a Ruby method, but it makes running a collect or map on ActiveRecord objects much easier. Whereas before, you would do this:

@members = Member.find(:all).map { |member| member.name }

Now, you can simplify it to this:

@members = Member.find(:all).map(&:name)

Model Calculations

This will let you do simple calculations on any ActiveRecord model (as long as the field you're calculating is numeric).

Student.average(:grade) # finds the average grade for all students (returns a float)
Student.maximum(:grade) # finds the highest grade
Student.minimum(:grade) # finds the lowest grade
Student.sum(:grade) # the sum of all grades

Custom ActiveRecord Associations

Let's say you have a model called BlogPost and one called Comment. A blog post has many comments, but you also have a boolean field on comments called approved that signifies if it's been decided that the comment is not spam (like most comments are). This is what your BlogPost model might look like:

class BlogPost < ActiveRecord::Base
  has_many :comments

You can add custom associations for approved_comments and unapproved_comments to your model to make fetching these comments a lot easier.

class BlogPost < ActiveRecord::Base
  has_many :comments
  has_many :approved_comments, :class_name => 'Comment', :conditions => 'approved=1'
  has_many :unapproved_comments, :class_name => 'Comment', :conditions => 'approved=0'

All you have to do is specify the class name of the associated model and the conditions of the find. This makes it possible to easily access these associations from within your views.

You can now show the number of approved comments for each post.

<%= @blog_post.title %> - <%= @blog_post.approved_comments.count %> Comments

You can also easily list out the approved comments.

<%- @blog_post.approved_comments.each do |comment| -%>
  <%= comment.author %> said:
  <%= comment.content %>
<%- end -%>

UPDATE: Shawn reminded me this week about named_scope, which was added in Rails 2.1. It makes custom associations a bit easier and more full-featured. You can get the same approved and non-approved comments with named_scope:

class Comment < ActiveRecord::Base
  belongs_to :blog_post
  named_scope :approved, :conditions => ["approved = ?", true]
  named_scope :unapproved, :conditions => ["approved = ?", false]

Notice that now the named_scope declarations go in the Comment model instead of the BlogPost model like the custom associations. You get the approved comments for a post with this line:

<%= blog_post.comments.approved %>

You can also combine named_scope calls when selecting records. Suppose our Comment model now has a named_scope for both approved and unapproved comments, as well as comments made by anonymous authors.

class Comment < ActiveRecord::Base
  belongs_to :post
  named_scope :approved, :conditions => ["approved = ?", true]
  named_scope :unapproved, :conditions => ["approved = ?", false]
  named_scope :anonymous, :conditions => ["name = ?", 'Anonymous']

You can use this to find all of the approved comments for a post where the author is 'Anonymous'.

<%= blog_post.comments.approved.anonymous %>

To add even more functionality to named_scope, you can add conditions to the call on the fly.

<%= post.comments.approved.all(:conditions => ["created_at > ?", 2.weeks.ago]) %>

This will pass the additional date condition to the find, making it possible to refine your searches even more.

Render Partial with Collection/Object

This is how I've always done my partials.

The view (index.html.erb):

<%- @posts.each do |post| -%>
  <%= render :partial => 'post', :locals => {:post => post} %>
<%- end -%>

The partial (_post.html.erb):

<%= post.title %> written by <%= post.author %>

I can simplify the call to the partial down to only one line of code (the partial itself will stay the same).

<div id="all_posts">
  <%= render :partial => 'post', :collection => @posts %>

By specifying the collection option, the view will call the partial post for each item in the @posts array.

But, let's say I wanted to call the partial for only one post. The old way:

<div id="single_post">
  <%= render :partial => 'post', :locals => {:post => @post} %>

Not terrible, but we can make it easier with the object option.

<div id="single_post">
  <%= render :partial => 'post', :object => @post %>

This will call the partial, and pass it only the object that we specify. Shorter and cleaner.

RJS with link_to_function

If you have several things on your page that need to be updated, and you want to do it with a javascript call instead of an AJAX call to the server, you can do it by passing a block to the link_to_function method.

Suppose this is my view:

<div id="list">
  <p id="list_title"><%= @list.title %></p>
  <div id="list_items">
    <%= render :partial => 'item', :collection => @list.items %>
  <%= link_to_function 'Change it up' do |page|
    page.replace_html 'list_items', 'New Item Title'
    page.hide 'list_items'
  end %>

This is a poor example, but hopefully you can see what I'm trying to illustrate here.

Simplified FIND in Rails 2.1

With the release of Rails 2.1, they've added some much-needed find methods for easily getting all, first and last records for a model.

@all_posts = Post.all
@first_post = Post.first
@last_post = Post.last

And, of course, you can pass conditions and order options to the new find methods.

@all_posts = Post.all(:order => :updated_at)
@first_post = Post.first(:conditions => ["title LIKE ?", '%Rails%'])
@last_post = Post.last(:order => 'created_at DESC')

Tagged: tutorialtipsrubyrails