objectified_sessions

ObjectifiedSessions

Encapsulate and carefully manage access to your Rails session by modeling it as an object that you add fields and methods to, rather than a free-for-all Hash.

By default, Rails models your session as a Hash. While this makes it really easy to use, it also makes it really easy to make a mess: as your app grows, you have to search the entire codebase for usage of session (a pretty common word that's certain to be used in many irrelevant ways, as well) to figure out how it's being used. It's easy for it to grow almost without bound, and hard to keep a team of developers in sync about how it's being used. Further, the otherwise-extremely-nice CookieStore exacerbates these problems — because you no longer have the power to change the sessions that are now stored in users' browsers, as cookies.

Using ObjectifiedSessions:

• You can define exactly what session fields can be used, and control access to them through accessor methods that you can override to do anything you want. You can validate stored data, apply defaults when returning data, and so on. You can ensure that data is carefully filtered to store it in the most-compact possible format, and unpack it before returning it. (For example, you can store values as simple integers in the session to save space, but read and write them using clear, easy symbols from client code.)
• You can eliminate the tension between using long, descriptive, maintainable names for session data — and hence wasting very valuable session storage space — and using compact, unmaintainable names to save space is gone. Storage aliases let you access data using a long, descriptive name, while ObjectifiedSessions automatically stores it in the session using a short, compact alias.
• You can automatically clean up old, no-longer-used session data: if requested, ObjectifiedSessions will automatically delete data from the session that is no longer being used. (This is switched off by default, for obvious reasons.)
• Inactive fields let you preserve data that you want to make sure you aren't currently using, but which you don't want deleted forever.
• Retired fields let you keep track, forever, of session fields that you used to use — and, with the CookieStore, may forever exist in inbound sessions — so you don't ever accidentally re-use the same name for different session data, causing potentially catastrophic effects.
• Explicit field definition lets you immediately see exactly what data you're using.
• There's absolutely no additional restriction on what you can store, vis-à-vis Rails' normal session support.

And, best of all, you can migrate to ObjectifiedSessions completely incrementally; it interoperates perfectly with traditional session-handling code. You can migrate call site by call site, at your own pace; there's no need to migrate all at once, or even migrate all code for a given session key all at once.

ObjectifiedSessions supports:

• Ruby 1.8.7, 1.9.3, 2.0.0, 2.1.0, or JRuby 1.7.9
• Rails 3.0.20, 3.1.12, 3.2.16, and 4.0.2.

These are, however, just the versions it's tested against; ObjectifiedSessions contains no code that should be at all particularly dependent on exact Ruby or Rails versions, and should be compatible with a broad set of versions.

Current build status:

Installation

Add this line to your application's Gemfile:

gem 'objectified_sessions'

And then execute:

$ bundle

Or install it yourself as:

$ gem install objectified_sessions

Usage

Quick Start

Simply installing the Gem won't break anything. However, before the #objsession call from inside a controller will work, you need to create the class that implements your session. The simplest way to do this is by running rails generate objectified_session; this will write a file to lib/objsession.rb that defines an empty objectified session.

To start storing data, you need to define one or more fields on your session:

class Objsession < ::ObjectifiedSessions::Base
  field :last_login
  field :user_id
end

...and now you can use it from controllers (or anywhere else, if you pass around the #objsession object) via:

objsession.last_login = Time.now
User.find(objsession.user_id)

...and so on.

The fields you define map exactly to traditional session fields — given the above, objsession.user_id and session[:user_id] will always return exactly the same value, and assigning one will assign the other. In other words, ObjectifiedSessions is not doing anything magical or scary to your session; rather, it's simply giving you a very clean, maintainable interface on top of the session you already know and love. You can assign any value to a field that is supported by Rails' traditional session, from an integer to an array of disparate Objects, or anything else you want.

Already, you have a single point where all known session fields are defined (assuming you're not using any old-style calls to #session). Read on for more benefits.

Adding Methods

You can, of course, define methods on this class that do anything you want — write fields, read fields, or simply answer questions:

class Objsession < ::ObjectifiedSessions::Base
  field :last_login
  field :user_id

  def logged_in!(user)
    self.last_login = Time.now unless self.last_login >= 5.minutes.ago
    self.user_id = user.id
  end

  def logged_in_today?
    self.last_login >= Time.now.at_midnight
  end
end

...and then, in your controllers, you can say:

def login!
  my_user = User.where(:username => params[:username])
  if my_user.password_matches?(params[:password])
    objsession.logged_in!(my_user)
  end
end

def some_other_action
  @logged_in_today = objsession.logged_in_today?
end

Private Methods

If you'd like to ensure your fields aren't modified outside the class, you can make them private:

class Objsession < ::ObjectifiedSessions::Base
  field :last_login, :visibility => :private
  field :user_id, :visibility => :private

  def logged_in!(user)
    self.last_login = Time.now unless self.last_login >= 5.minutes.ago
    self.user_id = user.id
  end

  def logged_in_today?
    self.last_login >= Time.now.at_midnight
  end
end

Now, if someone says objsession.last_login = Time.now in a controller, or objsession.user_id, they'll get a NoMethodError. Like all Ruby code, you can, of course, use #send to work around this if you need to.

If you want all methods to be private, you can set the default visibility, and then set fields' accessors to be public if you want them to be:

class Objsession < ::ObjectifiedSessions::Base
  default_visibility :private

  field :last_login
  field :user_id
  field :nickname, :visibility => :public
end

Overriding methods, Hash-style access, and super

You can override accessor methods; super will work properly, and you can also access properties using Hash-style access (which is always private, unless you use public :[], :[]= to make it public):

class Objsession < ::ObjectifiedSessions::Base
  field :user_type

  def user_type=(new_type)
    unless [ :guest, :normal, :admin ].include?(new_type)
      raise ArgumentError, "Invalid user type: #{new_type}"
    end

    super(new_type)
  end

  def user_type
    super || :normal
  end

  def is_admin?
    self[:user_type] == :admin
  end
end

Storage Aliasing

Unlike database columns, the names of session keys are embedded in every single instance of stored session data. You're often stuck in the tension between wanting to use long names to make your code readable, and short names to save precious session-storage space.

Enter storage aliases:

class Objsession < ::ObjectifiedSessions::Base
  field :custom_background_color, :storage => :cbc
end

Now, your controller looks like:

if objsession.custom_background_color
  ...
end

...while you're now using three, rather than 23, bytes of storage space for the key for that field.

IMPORTANT: Changing the storage alias for a field, or setting one, will cause all existing data for that field to disappear. (Hopefully this is obvious; this is because ObjectifiedSessions will now be looking under a different key for that data.) It is, however, safe to do the reverse, by renaming a field and setting its storage alias to be its old name.

Value Types

By default, ObjectifiedSessions will let you store any arbitrary Ruby object in the session — just like the default Rails session support will. However, this can cause significant issues, particularly with sessions; if you put, for example, a User model into the session, and then pull it out later (perhaps months later!), any attributes you added in the mean time will simply not be present. This is dangerous.

If you add this to your session class:

allowed_value_types :primitive

...then you will receive an ArgumentError if you try to store anything in the session other than nil, true, false, a String, a Symbol, a Numeric (including both integers and floating-point numbers), or a Time.

If you instead set this as follows:

allowed_value_types :primitive_and_compound

...then the rules are relaxed to also include Arrays and Hashes, as long as their constituent elements are valid simple scalars or themselves Arrays or Hashes. (In other words, you can nest these data types as deeply as you would like.)

If, for some reason, you need it, allowed_value_types :anything is the default setting.

Retiring Fields

Let's say you (probably wisely) stop supporting custom background colors, and remove that field. So far, so good.

Time passes, and now you introduce a session field saying whether or not the user has behaved consistently on your site in some way — a "consistent behavior check". You add an appropriate session field:

class Objsession < ::ObjectifiedSessions::Base
  field :consistent_behavior_check, :storage => :cbc
end

Uh-oh. Now you're going to start interpreting whatever data was there for your old custom_background_color field as consistent_behavior_check data, and bad, bad things may happen. (Using a CookieStore often makes this problem worse, since sessions can last an arbitrarily long time unless you set a cookie timeout — which has other disadvantages.)

To avoid this, when you remove a field, don't remove it entirely from the session class; instead, use the retired keyword instead of field:

class Objsession < ::ObjectifiedSessions::Base
  retired :custom_background_color, :storage => :cbc
end

Now, when you add the new consistent_behavior_check field...

class Objsession < ::ObjectifiedSessions::Base
  field :consistent_behavior_check, :storage => :cbc

  retired :custom_background_color, :storage => :cbc
end

...you'll get an error:

ObjectifiedSessions::Errors::DuplicateFieldStorageNameError (Class Objsession already has a field, :custom_background_color, with storage name "cbc"; you can't define field :consistent_behavior_check with that same storage name.)

Cleaning Up Unused Fields

Particularly if you're using the CookieStore to store session data, values for fields you no longer use may still be sitting in the session, taking up valuable space. You can tell ObjectifiedSessions to automatically remove any data that isn't defined as a field:

class Objsession < ::ObjectifiedSessions::Base
  unknown_fields :delete

  field :user_id
  field :last_login
  ...
end

Now, if, for example, a session is found that has a field cbc set, ObjectifiedSessions will automatically delete that key from the session.

Important Notes — BEFORE you use this feature, read these:

• You can LOSE DATA if you combine this with traditional session access. If you have code that reads or writes session[:foo], and you have no field :foo declared in your objsession, then ObjectifiedSessions will go around deleting field :foo from your session, breaking your code in horrible, horrible ways. Be absolutely certain that one of the following is true: (a) you're only using objsession to access session data, (b) you've defined a field in your objsession for any data that your traditional session code touches, or (c) use a prefix, as discussed below.
• Be aware of Gems or plugins that may use the session! These may be storing data in the session that you're not aware of, and that you won't discover by searching your codebase. To be safe, examine actual, real-world session data and the keys that it's using. (Iterating over all sessions in memcached, for example, or tracking keys used in all cookie-based sessions over the course of a whole day, can be very valuable, too.)
• Retired fields ARE deleted. This is because by retiring a field, you're saying, "I will never use this data again, but keep an eye on it for me to make sure I don't accidentally re-use that key". If you want to use unknown_fields :delete and don't want this behavior, use the inactive keyword instead of retired; it behaves identically (you can't access the data, and you can't define a field that conflicts), but it won't delete the data for that key.
• Be extremely careful when removing or retiring fields. This goes without saying, but, once you've deleted that data, it's gone forever. If you have any doubt, use inactive until you're certain.
• Deletion doesn't happen unless you actually instantiate the ObjectifiedSession, which only happens when you call objsession from inside a controller. This is intentional — we don't want ObjectifiedSessions to add any overhead whatsoever until you need it. If you want to ensure that this happens on every request, simply add a before_filter that calls objsession. (You don't need to read or write any fields, so simply calling objsession is sufficient.)

Partitioning Off the Session (Using a Prefix)

In certain cases, you may want ObjectifiedSessions to manage (and keep tidy) new session code, but want to make sure it cannot conflict at all with existing session data. In this case, you can set a prefix; this is a key under which all session data managed by ObjectifiedSessions will be stored.

For example — without the prefix:

class Objsession < ::ObjectifiedSessions::Base
  field :user_id
  field :last_login
end

objsession.user_id = 123
objsession.last_login = Time.now

session[:user_id]     # => 123
session[:last_login]  # => Thu Dec 26 19:35:55 -0600 2013

But with the prefix:

class Objsession < ::ObjectifiedSessions::Base
  prefix :p

  field :user_id
  field :last_login
end

objsession.user_id = 123
objsession.last_login = Time.now

session[:user_id]         # => nil
session[:last_login]      # => nil
session[:p]               # => { 'user_id' => 123, 'last_login' => Thu Dec 26 19:35:55 -0600 2013 }
session[:p]['user_id']    # => 123
session[:p]['last_login'] # Thu Dec 26 19:35:55 -0600 2013

Think carefully before you use this feature. In many cases, it is simply not necessary; ObjectifiedSessions interoperates just fine with traditional session-handling code. The only case where it's really required is if you have a very large base of code using the traditional session object, and you want to introduce ObjectifiedSessions bit by bit, and use unknown_fields :delete. This should be a very rare case, however.

Changing the prefix will make all your existing data disappear! Hopefully this is obvious, but setting the prefix makes ObjectifiedSessions look in a different place when reading or writing data; this means that changing it will cause all existing data to effectively disappear. Think carefully, choose whether to use a prefix or not, and then leave it alone.

Strings vs. Symbols

ObjectifiedSessions acts as a HashWithIndifferentAccess internally, so you can use either a String or a Symbol to access a given field when using Hash syntax, and you'll get the exact same result. It always talks to the Session using Strings, but this should be irrelevant in almost all cases.

(The only case where this actually matters is if you use a prefix; data stored under the prefix will be a Hash with Strings as keys, not Symbols.)

Changing the Objectified-Session Class, and Session Loading

If, for some reason, you want the class you use for your objectified session to be called something other than Objsession, you can change it like so in config/application.rb:

ObjectifiedSessions.session_class = :MyObjectifiedSession
# or ObjectifiedSessions.session_class = 'MyObjectifiedSession'
# or ObjectifiedSessions.session_class = MyObjectifiedSession
#   ...i.e., you can set a Class object itself

If you use either the String or Symbol form, then ObjectifiedSessions will attempt to require the corresponding file before resolving the class (but won't fail if that doesn't work — only if it still can't resolve the class afterwards). This means that the class you use does need to either already be loaded, or the file it's in needs to be named correctly and on one of Rails' load_paths.

Debugging and Other Tools

You can call #fields on the objectified-session object to get back an Array of Symbols, listing the fields that can be set on the session. You can call #fields on the objectified-session object to get back an Array of Symbols, listing the fields that have something set (besides nil — note, in this case, that false is distinct from nil) at present.

Calling #to_s or #inspect (which produce the same result) on the objectified session will produce a nice string containing, in alphabetical order, all data that's set on the session. Long data is abbreviated at forty characters; passing an argument of false to either of these methods will remove such abbreivation.

Migrating To ObjectifiedSessions

If you have an existing application and want to migrate to ObjectifiedSessions bit by bit, here's how I'd do it:

• Install the gem.
• Run the generator (rails generate objectified_session).
• Find some traditional session-handling code.
• Make sure there's a field declared in the ObjectifiedSession for whatever key the traditional session-handling code is using.
• Define methods on the ObjectifiedSession, if appropriate, to add appropriate functionality (value checking, question-answering, and so on) around this field.
• Change the traditional session-handling code to use objsession and the new methods.
• Test, commit, and deploy.
• Repeat steps 3-7.

The key point is that you don't have to migrate to ObjectifiedSessions all at once, or even all code that uses a single session field all at once.

Once you're done, and you're completely certain you've eliminated all use of traditional session code (and checked for Gems, plugins, or other code that may be using the session without your knowledge), you can set unknown_fields :delete, if you'd like.

Contributing

• Fork it
• Create your feature branch (git checkout -b my-new-feature)
• Commit your changes (git commit -am 'Add some feature')
• Push to the branch (git push origin my-new-feature)
• Create new Pull Request

Running Specs

ObjectifiedSessions is very thoroughly tested, including both system specs (that test the entire system at once) and unit specs (that test each class individually).

To run these specs:

• cd objectified_sessions (the root of the gem).
• bundle install
• bundle exec rspec spec will run all specs. (Or just rake.)