Setting and Retrieving Cookies






Setting and Retrieving Cookies

Problem

You want to set a cookie from within Rails.

Solution

Recall from Recipe 15.11 that all Rails controllers, views, helpers, and mailers have access to a method called sessions that returns a hash of the current client's session information. Your controllers, helpers, and mailers (but not your views) also have access to a method called cookies, which returns a hash of the current client's HTTP cookies.

To set a cookie for a user, simply set a key/value pair in that hash. For example, to keep track of how many pages a visitor has looked at, you might set a "visits" cookie:

	class ApplicationController < ActionController::Base
	  before_filter :count_visits

	  private

	  def count_visits
	    value = (cookies[:visits] || '0').to_i
	    cookies[:visits] = (value + 1).to_s
	    @visits = cookies[:visits]
	  end
	end 

The call to before_filter tells Rails to run this method before calling any action method. The private declaration makes sure that Rails doesn't think the count_visits method is itself an action method that the public can view.

Since cookies are not directly available to views, count_visits makes the value of the :visits cookie available as the instance variable @visits. This variable can be accessed from a view:

	<!-- index.rhtml -->
	You've visited this website's pages <%= @visits %> time(s).

HTTP cookie values can only be strings. Rails can automatically convert some values to strings, but it's safest to store only string values in cookies. If you need to store objects that can't easily be converted to and from strings, you should probably store them in the session hash instead.

Discussion

There may be times when you want more control over your cookies. For instance, Rails cookies expire by default when the user closes their browser session. If you want to change the browser expiration time, you can give cookies a hash that contains an :expires key and a time to expire the cookie. The following cookie will expire after one hour:[5]

[5] Rails extends Ruby's numeric classes to include some very helpful methods (like the hour method shown here). These methods convert the given unit to seconds. For example, Time.now + 1.hour is the same as Time.now + 3600, since 1.hour returns the number of seconds in an hour. Other helpful methods include minutes, hours, days, months, weeks, and years. Since they all convert to numbers of seconds, you can even add them together like 1.week + 3.days.

	cookies[:user_id] = { :value => '123', :expires => Time.now + 1.hour}

Here are some other options for a cookie hash passed into cookies.

The domain to which this cookie applies:

	:domain

The URL path to which this cookie applies (by default, the cookie applies to the entire domain: this means that if you host multiple applications on the same domain, their cookies may conflict):

	:path

Whether this cookie is secure (secure cookies are only transmitted over HTTPS connections; the default is false):

	:secure

Finally, Rails provides a quick and easy way to delete cookies:

	cookies.delete :user_id

Of course, every Ruby hash implements a delete method, but the cookies hash is a little different. It includes special code so that not only does calling delete remove a key-value pair from the cookies hash, it removes the corresponding cookie from the user's browser.

See Also

  • Recipe 3.5, "Doing Date Arithmetic"

  • Recipe 15.11, "Setting and Retrieving Session Information," has a discussion of when to use cookies and when to use session



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