Flowdock

Notes posted to Ruby on Rails

RSS feed
June 2, 2009 - (v2.2.1 - v2.3.2)
1 thank

Do not create an [ ] method

I created a helper method to access some meta data using

def [](name)
  # do stuff
end

This breaks ActiveRecord behaviors. all belongs_to relations were broken

eg.

class Image
  belongs_to :album
end

i = Image.find :first
i.album_id # 1
i.album # nil

Album.find 1 # works

If you experience this behavior, you probably created a method that breaks the default systematics (like I did with the [ ] method)

June 1, 2009 - (v2.2.1 - v2.3.2)
2 thanks

Further To: Memoize will not cache singleton methods

er…it will:

Code example

class PersonType < ActiveRecord::Base
  class << self
    # Add the mixin here:
    extend ActiveSupport::Memoizable
    def mister
      find_by_name('Mister')
    end
    memoize :mister
  end
end
June 1, 2009
2 thanks

Make sure your action names don't step on any toes.

In my experience, if you ever have a controller action named “process”, your controller will cease to function, as there is both a class and instance method called process in ActionController::Base.

There are undoubtedly other action names that will cause conflicts, but this one is particular I’ve run into a number of times.

May 31, 2009
2 thanks

You can call several times

You can call it several times, like:

class Comment < ActiveRecord::Base
  validate :must_be_friends
  validate :must_be_awesome
  ...

or with several arguments:

class Comment < ActiveRecord::Base
  validate :must_be_friends, :must_be_awesome
  ...
May 22, 2009
0 thanks

Alternative Way to Handle

This plugin may also help solve the problem from the model side.

http://github.com/rxcfc/multi_assignment_sanity
May 22, 2009 - (v2.0.0 - v2.1.0)
1 thank

Moved

In 2.2 and greater this has moved to ActiveSupport::Dependencies::Loadable#unloadable

May 19, 2009 - (v2.2.1 - v2.3.2)
2 thanks

How to set request parameters

On previous versions of TestRequest it was possible to set the request_parameters on the new action. This option is now gone, but it’s still possible to set the parameters after initialization.

Code example

request = ActionController::TestRequest.new
request.env["action_controller.request.request_parameters"] = { :foo => '42', :bar => '24' } 
May 15, 2009
0 thanks

script/generate can take table name

As far as I can tell script/generate will happily take the plural table name, at least in Rails 2.3.

May 12, 2009
2 thanks

form_authenticity_token

Instead of disabling the CSRF check you can pass the authenticity_token field in your forms, eg:

<%= hidden_field_tag :authenticity_token, form_authenticity_token -%>
May 8, 2009
2 thanks

Using gmail SMTP server to send mail

If you’re running Rails >= 2.2.1 [RC2] and Ruby 1.8.7, you don’t need plugin below. Ruby 1.8.7 supports SMTP TLS and Rails 2.2.1 ships with an option to enable it if you’re running Ruby 1.8.7.

All You need to do is:

ActionMailer::Base.smtp_settings = {
  :enable_starttls_auto => true
}
May 7, 2009
0 thanks

RESTful actions

REST adds many constraints. It restricts your controllers to seven actions. Normally this is okay, but sometimes you need to add your own custom actions.

http://railscasts.com/episodes/35-custom-rest-actions

May 7, 2009 - (v2.2.1 - v2.3.2)
1 thank

Question

Can someone add some more information to this?

May 6, 2009 - (>= v2.3.2)
1 thank

Formatted route helpers are gone

In Rails >= 2.3 you can’t use formatted_xxx url helpers anymore.

However, you can still pass a :format option to url helpers, eg:

articles_path(:format => :csv) # => /articles.csv
May 2, 2009 - (v2.0.0 - v2.3.2)
0 thanks

Setting name and id for select_tag

Sometimes you need to use select_tag instead of select (because you’re after more control or need to use optgroups, for example), but still want the id/name conventions that select would give.

In this case, all you need to do is set the first parameter to whatever would be produced by select, and it’ll take care of the id and name attribute automatically, and thus ensure the form data is parsed correctly after submission.

For example, if you want to do something like:

form_for :comment do |f|
 f.select :article_id ...

which would give a select tag with id of “comment_article_id” and a name attribute of “comment[article_id]”, which be parsed into the params hash of:

'comment' => {'article_id' => ...

you can instead do

form_for :comment do |f|
 select_tag 'comment[article_id]' ...

which will give the same id and name attributes for the select tag and hence the same params hash in the controller

May 2, 2009
0 thanks

Re: Find random record

How about if you wanted to find a random set of records instead of a singular record, what would be the best way?

Thank you

May 2, 2009
2 thanks

Re: Find random record

Ordering by RAND() is not a wise idea when you have a large table with lots of rows. Your database will have to calculate a different random value for every row in your database – O(N) – then sort the entire table by those values – O(N log N).

There are a number of better ways to get a random record from your table. Some examples:

  • If your table is not sparse, choose a random ID and get that row (or the nearest row):

rand_id = rand(Model.count)
rand_record = Model.first(:conditions => [ "id >= ?", rand_id]) # don't use OFFSET on MySQL; it's very slow
  • If your table is sparse, or does not have a primary key, consider adding an indexed column of random numbers between 0 and N. You can then order by this column quickly and choose a value using a method similar to the above example.

April 30, 2009
1 thank

Find random record

It’s as simple as:

Things.first(:order => 'RAND()')

Of course depending on your database it could be ‘RANDOM()’ or something similar.

April 30, 2009
1 thank

Caveat and design hints regarding :counter_cache

(From Obie Fernandez/ The Rails Way, ISBN 978-0321445612. Thanks Obie!)

This caveat:

The value of the counter cache column must be set to zero by default in the database! Otherwise the counter caching won’t work at all. It’s because the way that Rails implements the counter caching behavior is by adding a simple callback that goes directly to the database with an UPDATE command and increments the value of the counter.

And these tips:

If a significant percentage of your association collections will be empty at any given moment, you can optimize performance at the cost of some extra database storage by using counter caches liberally. The reason is that when the counter cache attribute is at zero, Rails won’t even try to query the database for the associated records!

If you’re not careful, and neglect to set a default value of 0 for the counter cache column on the database, or misspell the column name, the counter cache will still seem to work! There is a magic method on all classes with has_many associations called collection_count, just like the counter cache. It will return a correct count value if you don’t have a counter cache option set or the counter cache column value is null!

April 30, 2009
0 thanks

attachments and implicit multipart

There is a small gotcha - this caught me up for a while.

If you are using implicit multipart mime types by naming your template xxx.text.html.erb and xxx.text.plain.erb, you will need to change your template name back to the original xxx.erb.

If you use the implicit template name, your attachment will be the only thing in the body of the message - it will ignore your template.

See the “Multipart email” section of the ActionMailer.base documentation.

April 30, 2009
0 thanks

Video tutorial

If you want to get up to speed with Rails’ caching and haven’t seen it already, definitely check out this video series on Scaling Rails:

http://railslab.newrelic.com/scaling-rails

April 29, 2009 - (<= v2.3.2)
1 thank

Including instance methods to JSON output

Use :methods parameter to include ActiveRecord instance methods to JSON output. :only and :except uses DB columns only.

@events.to_json(:include => { 
                  :images => { 
                    :only => [], :methods => [:public_url] }})

In the previous example events have multiple images and only public_url instance method is included in the JSON output.

April 28, 2009
1 thank

Moved to ActiveSupport::Inflector

This isn’t gone, it’s just been moved to the ActiveSupport module namespace.

See: ActiveSupport::Inflector#pluralize

April 28, 2009
3 thanks

Tip: Define from_param(...) as Opposite

Often when defining a to_param method, it’s handy to introduce an opposite method for decoding them. For example:

class User < ActiveRecord::Base
  def self.from_param(param)
    find_by_name!(param)
  end

  def to_param
    name
  end
end

While you can just as easily redefine the find() method, this may be confusing since the expectation is that find() works with numerical IDs, or whatever the key column is defined as.

April 28, 2009 - (>= v2.3.2)
5 thanks

A very thorough explanation of use

Ryan Daigle has a great article about 2.3’s new nest forms which does a really good job of explaining how to use this and some of the potential gotchas. Highly recommended:

http://ryandaigle.com/articles/2009/2/1/what-s-new-in-edge-rails-nested-attributes

April 27, 2009 - (>= v2.0.0)
0 thanks

has_one through belongs_to not working

code example:

class Company < ActiveRecord::Base
  has_many :route_lists
end

class RouteList < ActiveRecord::Base
  belongs_to :company
  has_many :routes
end

class Route < ActiveRecord::Base
  belongs_to :route_list
  has_one :company :through => :route_list
end

This creates an invalid SQL query, where the keys in the join between route and routelist are switched, when used as an include:

Routes.find :all, :conditions => ["companies.type = ?", "Account"], :include => :company

route_lists.route_list_id = route.id

instead of: route_lists.id = route.route_list_id

April 25, 2009
4 thanks

Set :use_route to nil to let Rails pick the best route

Imagine the following case. You have two landing pages, one generic one, and an account specific one. The urls are as follows:

map.landing 'landing', :controller => 'landing', :action => 'index'
map.account_landing 'accounts/:account_id/landing', :controller => 'landing', :action => 'index'

Now imagine you want a path to the landing page, using the most specific route possible. If you have an account_id, use it, if not, skip it.

You could do

url_for(:controller => 'landing', :action => 'index', :account_id => current_account)

If current_account is set you’ll get “/accounts/:account_id/landing” if not, you’ll get “/landing”. However, that just looks ugly.

Enter :use_route => nil.

landing_path(:account_id => nil)                    # => '/landing'
landing_path(:account_id => 1)                      # => '/landing?account_id=1'
landing_path(:account_id => nil, :use_route => nil) # => '/landing'
landing_path(:account_id => 1, :use_route => nil)   # => '/accounts/1/landing'

Setting :use_route to nil, is equivalent to the earlier #url_for example.

April 24, 2009
2 thanks

have your to_param begin with the object's id

If you overwrite the to_param method in your model class such that it does not begin with its id, you can be in for a nasty surprise:

Example

class User
  def to_param
    self.login
  end
  ...
end

Let’s say you have a user called “bob”, than you might think this works:

>> bob = User.find(3)
=> #<User id: 3, login: "bob", ...>
>> User.find(bob.to_param)
ActiveRecord::RecordNotFound: Couldn't find User with ID=bob

But it’s not the reason being that Rails find method looks for a beginning number (d+) and uses that to look up the record (and ignores everything that comes after the last digit). So the solution is to have your to_param return something that begins with the object’s id, like so:

Example

class User
  def to_param
    "#{self.id}-#{self.login}"
  end
  ...
end

>> bob = User.find(3)
=> #<User id: 3, login: "bob", ...>

>> User.find(bob.to_param)

> # id: 3, login: “bob”, …>

>> bob.to_param

> “3-bob”

April 23, 2009
1 thank

Using strings as association names

Beware, that using strings as association names, when giving Hash to :include will render errors:

The error occurred while evaluating nil.name

So, :include => [‘assoc1’, ‘assoc2’ ] will work, and :include => [ {‘assoc1’ => ‘assoc3’}, ‘assoc2’] won’t. Use symbols:

Proper form

:include => [ {:assoc1 => :assoc3}, ‘assoc2’]

April 23, 2009 - (v2.0.0 - v2.3.2)
0 thanks

Real HTML_ESCAPE VALUE

Real value:

HTML_ESCAPE = { '&' => '&',  '>' => '>',   '<' => '<', '"' => '"' }
April 21, 2009
3 thanks

Format not coming out properly?

Date, Time and DateTime may have different formats defined.

If you do:

@user.created_at.to_formatted_s(:long_ordinal)

You will get (or something):

April 16th, 2009 22:03 

But if you do:

@user.created_at.to_date.to_formatted_s(:long_ordinal)

You will get:

April 16th, 2009

So, be sure you know which one you are working with.