Module CanCan::Ability
In: lib/cancan/ability.rb

This module is designed to be included into an Ability class. This will provide the "can" methods for defining and checking abilities.

  class Ability
    include CanCan::Ability

    def initialize(user)
      if user.admin?
        can :manage, :all
      else
        can :read, :all
      end
    end
  end

Methods

Public Instance methods

Alias one or more actions into another one.

  alias_action :update, :destroy, :to => :modify
  can :modify, Comment

Then :modify permission will apply to both :update and :destroy requests.

  can? :update, Comment # => true
  can? :destroy, Comment # => true

This only works in one direction. Passing the aliased action into the "can?" call will not work because aliases are meant to generate more generic actions.

  alias_action :update, :destroy, :to => :modify
  can :update, Comment
  can? :modify, Comment # => false

Unless that exact alias is used.

  can :modify, Comment
  can? :modify, Comment # => true

The following aliases are added by default for conveniently mapping common controller actions.

  alias_action :index, :show, :to => :read
  alias_action :new, :to => :create
  alias_action :edit, :to => :update

This way one can use params[:action] in the controller to determine the permission.

Returns a hash of aliased actions. The key is the target and the value is an array of actions aliasing the key.

See ControllerAdditions#authorize! for documentation.

Defines which abilities are allowed using two arguments. The first one is the action you‘re setting the permission for, the second one is the class of object you‘re setting it on.

  can :update, Article

You can pass an array for either of these parameters to match any one. Here the user has the ability to update or destroy both articles and comments.

  can [:update, :destroy], [Article, Comment]

You can pass :all to match any object and :manage to match any action. Here are some examples.

  can :manage, :all
  can :update, :all
  can :manage, Project

You can pass a hash of conditions as the third argument. Here the user can only see active projects which he owns.

  can :read, Project, :active => true, :user_id => user.id

See ActiveRecordAdditions#accessible_by for how to use this in database queries. These conditions are also used for initial attributes when building a record in ControllerAdditions#load_resource.

If the conditions hash does not give you enough control over defining abilities, you can use a block along with any Ruby code you want.

  can :update, Project do |project|
    project.groups.include?(user.group)
  end

If the block returns true then the user has that :update ability for that project, otherwise he will be denied access. The downside to using a block is that it cannot be used to generate conditions for database queries.

You can pass custom objects into this "can" method, this is usually done with a symbol and is useful if a class isn‘t available to define permissions on.

  can :read, :stats
  can? :read, :stats # => true

IMPORTANT: Neither a hash of conditions or a block will be used when checking permission on a class.

  can :update, Project, :priority => 3
  can? :update, Project # => true

If you pass no arguments to can, the action, class, and object will be passed to the block and the block will always be executed. This allows you to override the full behavior if the permissions are defined in an external source such as the database.

  can do |action, object_class, object|
    # check the database and return true/false
  end

Check if the user has permission to perform a given action on an object.

  can? :destroy, @project

You can also pass the class instead of an instance (if you don‘t have one handy).

  can? :create, Project

Nested resources can be passed through a hash, this way conditions which are dependent upon the association will work when using a class.

  can? :create, @category => Project

Any additional arguments will be passed into the "can" block definition. This can be used to pass more information about the user‘s request for example.

  can? :create, Project, request.remote_ip

  can :create Project do |project, remote_ip|
    # ...
  end

Not only can you use the can? method in the controller and view (see ControllerAdditions), but you can also call it directly on an ability instance.

  ability.can? :destroy, @project

This makes testing a user‘s abilities very easy.

  def test "user can only destroy projects which he owns"
    user = User.new
    ability = Ability.new(user)
    assert ability.can?(:destroy, Project.new(:user => user))
    assert ability.cannot?(:destroy, Project.new)
  end

Also see the RSpec Matchers to aid in testing.

Defines an ability which cannot be done. Accepts the same arguments as "can".

  can :read, :all
  cannot :read, Comment

A block can be passed just like "can", however if the logic is complex it is recommended to use the "can" method.

  cannot :read, Product do |product|
    product.invisible?
  end

Convenience method which works the same as "can?" but returns the opposite value.

  cannot? :destroy, @project

Removes previously aliased actions including the defaults.

User shouldn‘t specify targets with names of real actions or it will cause Seg fault

[Validate]